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General Science => General Science => Topic started by: NakedScientist on 29/08/2003 00:21:58

Title: Question of the Week - Old Version
Post by: NakedScientist on 29/08/2003 00:21:58
A new feature, starting this week is "Question of the Week".

We'll post the question initially, everyone can have a go at answering it, then we'll hit you with the answer at the end of the week, together with the new question.

Please feel free to submit appropriate questions via our contact page :

http://www.thenakedscientists.com/html/contacts.htm

Here's the first question :

"Why do we get goosebumps"

Fire away...

TNS
Title: Re: Question of the Week - Old Version
Post by: Broca on 29/08/2003 02:33:14
Our ancesters had much more hair than we do. In those days, when they became cold they would get goosebumps as a skin response which would raise the hairs on their body. By raising the hairs on their body the air could not circulate as easily thus creating a type of insulation. The air would be warmed by the body heat which in turn would warm them. We have less hair than those who came before us, we still have the same skin response however, and the goosebump is a raise in the skin where the hair protrudes and we can see it easier since we do not have the same amount of hair covering our bodies.
Title: Re: Question of the Week - Old Version
Post by: bezoar on 29/08/2003 03:24:45
Do animals get goosebumps?  Or at least primates?

Bezoar
Title: Re: Question of the Week - Old Version
Post by: Broca on 29/08/2003 03:30:47
Yes, animals get goosebumps as well. They get them for the same reason humans do and also animals get them to make themselves look a tad bigger when threatened. It is a survival adaptation.
Title: Re: Question of the Week - Old Version
Post by: Ians Daddy on 29/08/2003 04:06:37
Do we get goosebumps when frightened for the same reason?
Title: Re: Question of the Week - Old Version
Post by: Broca on 29/08/2003 04:15:51
I would guess yes, but am not certain. I would think it would again be an adaptaion for survival from when we were covered in hair.
Title: Re: Question of the Week - Old Version
Post by: NakedScientist on 05/09/2003 22:41:32
ANSWER TO LAST WEEK'S QUESTION : "WHY DO WE GET GOOSEPIMPLES / GOOSEBUMPS ?"

We have inherited this rather bizarre phenomenon from our hairier ancestors. Goosepimples, or goosebumps (as the Americans prefer to call them), are elevations in the skin at the base of hairs. They occur when a tiny muscle called a piloerector muscle (from the latin word PILUS meaning a hair) contracts to lift up the hair.

In hairier animals, making the hair stand up like this helps to trap an insulating layer of air against the skin which, in turn, cuts down heat loss and hence preserves body temperature. That's why they appear when you get cold.

The more observant among you will also have noticed that goosbumps can also appear when you are nervous or frightened. This is also the origin of the saying "feeling the hairs on the back of my neck stand up" and that's because the nerves which supply the piloerector muscles are also activated by fear. The evolutionary benefit of this is that an animal which makes its fur stand on end appears larger than it really is, and hence is more likely to scare off its opponent in a challenge situation. The situation is somewhat analogous to a puffer fish expanding when frightened.

So there you have it, the cause of goosebumps.

This week's question is below.
Title: Re: Question of the Week - Old Version
Post by: NakedScientist on 05/09/2003 22:43:24
THIS WEEK'S QUESTION : - Have a go - brownie points to the person who gets closest to the correct answer, which we'll post in a week's time.

"WHY IS THE SKY BLUE ?"
Title: Re: Question of the Week - Old Version
Post by: cuso4 on 06/09/2003 11:35:44
Right this is a guess.

We see colours because objects absorb some wavelengths of light and reflect others. So a sensible guess is that the water particles in the atmosphere absorbs all the colours but blue. And the blue light reflects into our eyes that's why we see blue.

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Title: Re: Question of the Week - Old Version
Post by: Exodus on 06/09/2003 12:18:12
Christopher, does this have something to do with good old Lord Rayleigh?

Resident Tour Operator - The Naked Scientists
Title: Re: Question of the Week - Old Version
Post by: Ians Daddy on 06/09/2003 15:15:28
Reflection of the ocean.
Title: Re: Question of the Week - Old Version
Post by: cuso4 on 07/09/2003 20:28:28
Ronnie, I originally thought about this answer as well but then I questioned why the ocean has that blue colour,the colour is due light that shines on it. Deeper the ocean the darker the colour, if what you said is true why doesn't the colour of the sky become a darker blue?

Another question came to my mind, why is the sky appear orange/yellow during sunset? (or may be it's the cloud?)

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Title: Re: Question of the Week - Old Version
Post by: Ians Daddy on 08/09/2003 01:08:57
I may have that backwards. Maybe the ocean is blue because it is reflecting the sky. It seems that I learned that it was reflection. I remember that it is due to the prysm effect. Diffused light through water droplets.

In fact, I believe you are correct, it would be the clouds that made it yellow / orange / red. Due to the angle of the sun i.e. morning / evening, and the density of the water of the clouds. I guess that when the sun is low, its refracting the light as reds and when the sun is high, it would be blue...less break up? What makes a gray sky?
Title: Re: Question of the Week - Old Version
Post by: cuso4 on 08/09/2003 08:09:35
Air pollution?

Angel
Title: Re: Question of the Week - Old Version
Post by: NakedScientist on 12/09/2003 11:44:36
ANSWER TO "WHY IS THE SKY BLUE ?" :

The sky is blue due to an effect of the earth's atmosphere on the light reaching us from the sun.

Although sunlight looks 'white' it is actually made up of a whole spectrum of colours which you can see in a rainbow, or with a prism. The different coloured lights have different wavelengths ranging from blue light (which has the shortest wavelength) to red light which has the longest.

The Blue light is strongly scattered by the oxygen and nitrogen in the atmosphere, whilst the other colours, with longer wavelengths, are not affected.

This means that when light waves arrive from the sun, some of the blue light is bounced about and scattered in all directions by the air so that it no longer seems to be coming just from one place - the sun - and instead the whole sky seems blue. But the rest of the light (with longer wavelengths) passes unaffected straight through the atmosphere to your eye and hence the sun looks a yellowy red colour (white minus some of the blue).

So why does the sun go red at sunset ?

This is because as the sun 'sinks' the light has to travel further through the atmosphere to reach your eye meaning that more of the blue (and shorter wavelength light) is scattered (removed) than when the sun is high in the sky, making the sun look even more red.

TNS
Title: Re: Question of the Week - Old Version
Post by: NakedScientist on 12/09/2003 11:49:24
THIS WEEK'S QUESTION OF THE WEEK :

"WHY DON'T PENGUINS FEET FREEZE ?"
Title: Re: Question of the Week - Old Version
Post by: noden1 on 12/09/2003 22:55:33
if they did you would not be able to pick up a penguin!!!
Title: Re: Question of the Week - Old Version
Post by: Qing on 13/09/2003 15:46:23
I guess they might have some kind of fat under the skin which will generate heat and provent from freezing. But as I said, it's only a guess and I've no idea.

Qing
Title: Re: Question of the Week - Old Version
Post by: cuso4 on 15/09/2003 20:13:04
Penguin's feet are covered by its thick waterproof fur which can trap air and act as insulation. And I guess their feet are padded with ... probably fat which again acts as insulation

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Title: Re: Question of the Week - Old Version
Post by: Ians Daddy on 15/09/2003 23:48:36
THIS WEEK'S QUESTION OF THE WEEK :

"WHY DON'T PENGUINS FEET FREEZE ?"

A penguin's feet are like a duck's feet, so they don't have any protective layers of hair or fat. I would guess that it would have to do with an internal thermostat. Cold / warm blooded creatures must adapt to their surroundings. Maybe it's the lack of blood that keeps their feet from freezing up. Or, maybe their pumped full of hot blood that is heated from their little fat bodies.
Being flightless, they have no alternative but to adapt. Besides, their easier to punt when they're not stuck to the ground.

Just a thought.
Title: Re: Question of the Week - Old Version
Post by: Broca on 16/09/2003 18:42:11
Ahhh another science adaptation question...critical curriculum in the 4th grade.
Penguins are able to slow the blood supply to their feet keeping the temperature of them above freezing. Their feet might be really cold, but they will not succumb to frost bite.
Title: Re: Question of the Week - Old Version
Post by: bezoar on 16/09/2003 20:02:43
But it would seem like slowing the blood supply to their feet would cool the feet, making them more susceptible to freezing.
Title: Re: Question of the Week - Old Version
Post by: Donnah on 17/09/2003 00:59:03
Don't they cover their feet with their pot bellies when they are not moving?  So I'm guessing their feet are kept thawed by movement and/or fat-belly cover.
Title: Re: Question of the Week - Old Version
Post by: cuso4 on 17/09/2003 09:06:17
Now I got another theory.

May be cells of penguins feet are surrounded with networks of cappilaries and this enables oxygen to be transported to the cells in the feet. So that energy can be generated by respiration to keep their feet warm.

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Title: Re: Question of the Week - Old Version
Post by: bezoar on 18/09/2003 05:33:14
Seems like this would have to do with some type of mechanism or anatomy that keeps both the venous and arterial blood above freezing.  And obviously, the venous blood would be the greater problem.

Bezoar
Title: Re: Question of the Week - Old Version
Post by: Ians Daddy on 18/09/2003 05:47:16
I'm going to stray a bit, because this is where I am. Does anyone know what happened to "Nilmot" / Tom / "The Riddler"? Haven't seen him in quite awhile.
Title: Re: Question of the Week - Old Version
Post by: Qing on 18/09/2003 09:31:22
quote:
Originally posted by cuso4

Now I got another theory.

May be cells of penguins feet are surrounded with networks of cappilaries and this enables oxygen to be transported to the cells in the feet. So that energy can be generated by respiration to keep their feet warm.

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I came up with this idea as well, but this might not be enough.i mean, penguins feet are in direct contact with freezing enviornment,and the tempearture is really low. so there might be other adaptations e.g. like Donnah said,"they cover their feet with their pot bellies when they are not moving". just a thought.

Qing
Title: Re: Question of the Week - Old Version
Post by: NakedScientist on 19/09/2003 01:24:10
ANSWER TO : WHY DONíT PENGUINS FEET FREEZE ?
Part of the reason is that penguins are birds and are warm blooded so they keep their feet from freezing by pumping warm blood from their body into them. But thatís only half the story because penguins live in such a cold environment that they would very quickly lose all of their body heat if they continuously pumped hot blood around their feet. Instead they have hit upon an ingenious solution which saves heat and keeps their feet just above freezing. In the penguinís legs the arteries, which carry hot blood from the body, are wrapped around the veins bringing cold blood back from the feet. The cold blood in the veins removes most of the heat from the arteries, warming up as it does so, so that the blood entering the feet is just above freezing, but the blood in the veins, by the time it reaches the body, is back up to body temperature. So the penguins feet receive blood just warm enough to keep them from freezing, but are not so hot that the penguin melts into the ice.
Title: Re: Question of the Week - Old Version
Post by: NakedScientist on 19/09/2003 01:25:54
HERE'S THIS WEEK'S "QUESTION OF THE WEEK" :

"HOW, AND WHY, DO CHAMELEONS CHANGE COLOUR ?"

Fire away.

TNS
Title: Re: Question of the Week - Old Version
Post by: Qing on 19/09/2003 15:51:13
that's an interesting question. i know that chameleons change colour to protect themselves. their colour changes according to the environment. but how do they change it.

Qing
Title: Re: Question of the Week - Old Version
Post by: Ians Daddy on 20/09/2003 02:47:33
Surely it's chemical. Maybe it detects the light rays emmiting from a surface and can balance itself to that. It's probably automatic, the same way that I turn so red when embarrassed or angry. When frightened, they "balance" themselves with their surroundings. [?]
Title: Re: Question of the Week - Old Version
Post by: Exodus on 20/09/2003 09:45:04
I've always considered myself to have chameleon properties... If i drink too much i turn green too, what help that does i dont know, when your in that state you want to be found, not blend in with the grass! LOL

As for th answer, i don't really know, well i have an idea...

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Title: Re: Question of the Week - Old Version
Post by: cuso4 on 24/09/2003 09:05:13
quote:
Originally posted by NakedScientist

ANSWER TO : WHY DONíT PENGUINS FEET FREEZE ?
Part of the reason is that penguins are birds and are warm blooded so they keep their feet from freezing by pumping warm blood from their body into them. But thatís only half the story because penguins live in such a cold environment that they would very quickly lose all of their body heat if they continuously pumped hot blood around their feet. Instead they have hit upon an ingenious solution which saves heat and keeps their feet just above freezing. In the penguinís legs the arteries, which carry hot blood from the body, are wrapped around the veins bringing cold blood back from the feet. The cold blood in the veins removes most of the heat from the arteries, warming up as it does so, so that the blood entering the feet is just above freezing, but the blood in the veins, by the time it reaches the body, is back up to body temperature. So the penguins feet receive blood just warm enough to keep them from freezing, but are not so hot that the penguin melts into the ice.




Just found out that human (and other mammals) keep their hands and feet from freezing the same way as penguins. Because we are all HOMEOTHERMS.

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Title: Re: Question of the Week - Old Version
Post by: cuso4 on 24/09/2003 09:11:53
quote:
Originally posted by NakedScientist

HERE'S THIS WEEK'S "QUESTION OF THE WEEK" :

"HOW, AND WHY, DO CHAMELEONS CHANGE COLOUR ?"

Fire away.

TNS



Here's the answer. This is not purely my knowledge because I did a bit of research.

Under a chameleon°Įs outer skin are special skin cells with colour (or pigment) in them. These cells are called chromatophores. The top layer of chromatophores have red or yellow pigment. The lower layers have blue or white pigment. A chameleon changes colour when its brain sends a message to the cells. The message tells the cells to grow bigger or to shrink. When this happens, the cell pigments mix and the chameleon°Įs colour changes.

Temperature affects the chameleon°Įs colour too°™if it°Įs cold, darker skin allows the chameleon to absorb more heat from the Sun. And, light from the Sun can signal a chameleon to change to a lighter shade, to reflect the sunlight.

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Title: Re: Question of the Week - Old Version
Post by: NakedScientist on 29/09/2003 19:05:51
ANSWER TO "HOW DO CHAMELEONS CHANGE COLOUR ?"


If youíre not sure what a chameleon is, itís a kind of lizard that lives in trees, usually in Africa or Madagascar. Most people have heard of chameleons because of their amazing ability to change the colour of their entire body within seconds. But itís a myth that  chameleons change their colour to blend in with their surroundings. In fact the main reason that they change colour is so that they can communicate with each other. For example a calm chameleon is a pale green colour, an angry chameleon turns bright yellow and a chameleon who spots another chameleon it would like to mate with usually displays an explosion of different colours including reds, greens, browns, whites and blues. So how do they actually change colour. The answer lies in special cells buried in their skin called chromatophores. These cells are all wired up to the chameleonís brain and contain different coloured pigments. When the chameleon wants to change colour, signals from the brain tell the skin cells to release their coloured pigment which spreads out in the cell and changes its colour, rather like giving the cell a coat of paint. The chameleon can make a range of different colours by switching on different coloured pigment cells at the same time, a bit like mixing red and yellow paint together to make orange.

WELL DONE ANGEL - HIT THE NAIL ON THE HEAD !
Title: Re: Question of the Week - Old Version
Post by: NakedScientist on 29/09/2003 19:07:53
HERE IS THIS WEEK'S "QUESTION OF THE WEEK" :

"WHY DO PEOPLE HAVE DIFFERENT COLOURED SKINS ?"

Have a go, answer next week.

TNS
Title: Re: Question of the Week - Old Version
Post by: Ians Daddy on 30/09/2003 00:18:14
Different levels of melanin?
Title: Re: Question of the Week - Old Version
Post by: cuso4 on 30/09/2003 09:27:53
Yes Ronnie, I believe so.

I think different levels of melanin are due to human's adaptation to the environment. The pigment melanin can absorb UV radiation to prevent the damage to skin cells.

For example, people live in Africa are constantly exposed to strong sunlight during day time, so their ancester had evolved (not sure it's the right word to use) to have a dark skin to suit the environment.

However, people live in places like UK or Canada where the weather is colder and experience less sunlight had not adapted for exposure to sunlight but for the reduction of heat lost. Although pale colour absorb less heat they also radiate less heat.

Finally, people live in Asia especially with sub-tropical weather are adapted for medium level of sun exposure. This accounts for their tan-ish coloured skin.

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Title: Re: Question of the Week - Old Version
Post by: Quantumcat on 30/09/2003 09:57:03
darn it cuso4, that's my kind of question!![:(!] I was too late[:(] lol only kidding I'm not mad !![:)]

I can add a little bit.

When humans have little or no pigment, that is, albanism, it's because there is a mutation in the gene for tyrosinase which is an enzyme that changes tyrosine into melanin in the melanocytes.

People with darker skin have extra genes (I think, correct me if I'm wrong!!!) that increase tyrosinase production so more melanin is converted from tyrosine in the melanocytes, then let out and distributed around the skin...

When the skin is exposed to UV light, tyrosinase production is stepped up so more melanin is made. This is an emergency response designed to protect the skin from further damage from the UV light (because UV radiation can change genes, therefore cause cancer)

Tyrosinase is being made all the time, melanin isn't permanent and if you get a tan then stay is a dark room for a while you'll see that the tan wears off in a month or so.

When people get freckles it's because the melanocytes are spaced far from each other and aren't very efficent at delivering the melanin into the surrounding skin (also correct me of I'm wrong there not so sure)

Anyway I didn't copy and paste that, I wrote it from my own head ... probably why some of it is probably wrong ... lol

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Title: Re: Question of the Week - Old Version
Post by: cuso4 on 30/09/2003 13:33:12
Sorry Quantum [|)], but my bit is quite simple and can be worked out logically whereas your bit is....very scientific (good on you [:D]!) and thanks for the extra info as I didn't know melanin was made from tyrosine.

And...I'm certain that the bit about freckles is correct. People who get tan because they got even distribution of melanocytes.

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Title: Re: Question of the Week - Old Version
Post by: Ians Daddy on 30/09/2003 13:35:30
How long does the "evolution" take to adapt to the amount of sun? ie.. transplanted people from different regions. I know that a tan would fade, but how does and how long for the melocytes to alter?

Why do freckles fade with age in some people? ie... kids with freckles on their noses.[:o)]

Why do I turn deep red [:(!](not a burn)[V] as opposed to brown when I'm in the sun alot?

Just some thoughts.
Title: Re: Question of the Week - Old Version
Post by: cuso4 on 01/10/2003 08:42:10
May be you don't have enough melocytes to produce a tan. Instead, the capillaries near the surface of your skin expand allowing more blood flow, you therefore lose heat through radiation and convection. This is vasodilation.

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Title: Re: Question of the Week - Old Version
Post by: Qing on 01/10/2003 08:57:45
why do people get headache [xx(] after being exposed to bright sunlight for a long time perticularly if you skin colour is light?

Qing
Title: Re: Question of the Week - Old Version
Post by: cuso4 on 01/10/2003 13:57:19
Don't people get overheated and the enzymes in the body start malfunctioning?

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Title: Re: Question of the Week - Old Version
Post by: Donnah on 01/10/2003 22:43:26
Ronnie, maybe you turn red due to your Indian heritage.  

As for the geographic effect of the sun over the course of generations, why are Eskimo and Inuit people, who live in the far north, dark skinned?
Title: Re: Question of the Week - Old Version
Post by: Ians Daddy on 01/10/2003 23:35:36
Maybe the elevation. Or, the reflective affect of the snow and sun. Actually, maybe the evolutionary adaptation period is very slow and these people are decendants from a southern race. It's fascinating to see that Eskimo, Somoan, Polinesian, Mexican, Native American Indian and Asian people have very present similarities in skin tone and features. So, maybe our "family tree" is more narrow than we thought.
Title: Re: Question of the Week - Old Version
Post by: Quantumcat on 02/10/2003 09:44:41
Snow reflects more light than soil, a lot more. Either that or they haven't lived in the far north for very long.

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Title: Re: Question of the Week - Old Version
Post by: Donnah on 03/10/2003 01:34:09
There's also the issue of constant daylight in northern summers, and constant dark in winter.
Title: Re: Question of the Week - Old Version
Post by: bezoar on 03/10/2003 06:02:47
I seem to remember, way back in high school, being taught that it isn't the number of melanocytes, but the size of the granules of melanin that makes for the differences in skin color.  Any feedback on that?

Bezoar
Title: Re: Question of the Week - Old Version
Post by: Quantumcat on 03/10/2003 09:45:53
Oh, yes!! That's it. In summer their nights would be like one hour long. But, their days in winter would be like one hour long too, so it doesn't work. Bugger.

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Title: Re: Question of the Week - Old Version
Post by: NakedScientist on 07/10/2003 02:16:53
ANSWER TO "WHY DO PEOPLE HAVE DIFFERENT COLOURED SKINS ?"
 
Itís all down to a substance called melanin, the stuff that suntans are made of. The body produces melanin, which is a dark brown colour, to protect us from the sun because melanin stops harmful ultraviolet rays that can cause sunburn and skin cancer. People with dark skins naturally make much more melanin than fair-skinned people and thatís why their skin is browner. Most of these people have ancestors from hot countries where there is a lot of strong sun and so they have their own natural sun-block. Scientists think that our ancient ancestors came from Africa and all had dark skins to protect them from the sun. But, over thousands of years as they migrated out of Africa to inhabit colder countries, it was no longer an advantage to have a dark skin because there was less sunlight, so people lost their natural sun-protection and became fair skinned.
Title: Re: Question of the Week - Old Version
Post by: NakedScientist on 07/10/2003 02:18:17
This week's question of the week was suggested by Tom (Nilmot)

WHY CAN YOU SOMETIMES SEE THE SUN AND MOON IN THE SKY TOGETHER ?

Have a go below...answer next week.

TNS
Title: Re: Question of the Week - Old Version
Post by: Donnah on 07/10/2003 23:26:48
Why wouldn't you be able to see them both?  The sun emits light and the moon reflects that light.  It just depends on where they are relative to the observer's field of vision.
Title: Re: Question of the Week - Old Version
Post by: chris on 08/10/2003 01:00:06
Quick comment to Bezoar in relation to her remark about melanocytes - yes you are definitely right. The melanocyte density is equivalent in black and white people. However, the expression of melanin and the cellular environment differs to make black people produce more melanin overall.

Chris

"I never forget a face, but in your case I'll make an exception"
 - Groucho Marx
Title: Re: Question of the Week - Old Version
Post by: Qing on 08/10/2003 09:52:43
usually,when we see the sun and the moon appear in the sky together will either be break or dawn except when there is a solar or lunar eclipse,so what I am thinking is that it depends on the angle the earth "lays"and the orbital it is "running" aroud the sun and also how the moon orbiting around the earth.besides this,I guess there must be something to do with at which latitude you are standing and observing from. I vaguely remember when I was in school I was taught that the orbital of the earth travelling around the sun is not horizontal,it's kind of oblique,a few degrees to the horizontal.
These just pure guesses,and don't know how to explain it clearly[:(]hope you can all understand me.

Qing
Title: Re: Question of the Week - Old Version
Post by: NakedScientist on 17/10/2003 13:37:49
HERE'S THE ANSWER TO LAST WEEK'S "QUESTION OF THE WEEK", SUBMITTED BY NILMOT (Tom Lin)

The appearence of the moon in the sky depends upon the position of its orbit. There is no reason why the moon and sun should not appear together in the sky since they are totally independent of each other. The moon orbits the earth and the earth orbits the sun. Therefore sometimes the moon coincide on its orbit with the rising of he sun and hence the two will appear in the sky together.

This is precisely how an eclipse occurs, only on this occcasion the path of the moon crosses the path of the sun. But the two bodies are still in the sky at the same time.

I think most people seemed to get that one right. Good question though. By an amazing co-incidence a lady phoned the radio show a few weeks ago with the same question !
Title: Re: Question of the Week - Old Version
Post by: NakedScientist on 17/10/2003 13:41:08
THIS WEEK'S QUESTION OF THE WEEK

"HOW DO WE KNOW HOW HOT THE SUN IS SINCE WE CAN'T GO AND MEASURE IT ?"

TNS
Title: Re: Question of the Week - Old Version
Post by: Ians Daddy on 17/10/2003 15:01:01
Guessing....will take a better stab at it later after some thought.
Guess: Temp. x Distance

I know that's probably wrong, but I'll build on it.
Title: Re: Question of the Week - Old Version
Post by: Quantumcat on 17/10/2003 22:19:43
colours - the material of anything burns at different colours depending on the temperature and what the materials are

we know what the materials are from the spectrum

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Title: Re: Question of the Week - Old Version
Post by: cuso4 on 22/10/2003 17:17:30
Is this called the BLACK BODY RADIATION? Never mind me if I'm talking rubbish.

Angel (https://www.thenakedscientists.com/forum/proxy.php?request=http%3A%2F%2Fsmilies.jeeptalk.org%2Fups%2Ficis%2Fices_angel_g.gif&hash=eb252a305c5a566cd34544de7a761914)
Title: Re: Question of the Week - Old Version
Post by: tweener on 23/10/2003 04:49:35
quote:
Originally posted by cuso4

Is this called the BLACK BODY RADIATION? Never mind me if I'm talking rubbish.

Angel (https://www.thenakedscientists.com/forum/proxy.php?request=http%3A%2F%2Fsmilies.jeeptalk.org%2Fups%2Ficis%2Fices_angel_g.gif&hash=eb252a305c5a566cd34544de7a761914)



Black Body Radiation is correct.  The spectrum of the radiation given by any body that has a temperature above absolute zero has a certain shape and the location of the peak and the distribution change with temperature.  So, it doesn't matter what the body is made of, you can measure its temperature by measuring the radiation it emits.

The universe is emitting radiation in the microwave range (wavelength of several cm) which gives it a temp of about 3 degrees Kelvin.  Red hot steel is emitting in the red end of visible light (wavelength about 700 nm), and the Sun emits in the visible and higher (wavelength around 500 nm) with a surface temperature of 5800 K.  The core is about 15 million degrees K.

To find out what it is made of, again measure the radition, but look for other things.  Each element and molecule will emit or absorb radiation strongly at certain wavelengths.  Looking at the spectrum, these appear as bright or dark lines.  The selectivity is caused by the quantum nature of the electrons in the outer part of the atom or molecule and how the electrons can behave in their orbits. Each element and molecule is very distinct.  Because they are all bunched together, the lines are spread out because of all the collsions the particles are undergoing.

Another book, but this is fun!

John

------------------------
No words of wisdom here.
Title: Re: Question of the Week - Old Version
Post by: NakedScientist on 27/10/2003 22:45:51
Since John explained it so beautifully, there is virtually nothing I can add to the answer to last week's question "How do we know how hot the sun is?". The answer is indeed by spectroscopy - the colour of the sun indicates its surface temperature. Some experienced steel workers can predict, to within 1 degree accuracy, the temperature of their steel, just by looking at its colour.

Well done everyone.

TNS
Title: Re: Question of the Week - Old Version
Post by: NakedScientist on 27/10/2003 22:47:30
Here is this week's Question of the Week :

"HOW DO BACTERIA BECOME RESISTANT TO THE EFFECTS OF ANTIBIOTICS?"

Have a stab below...

TNS
Title: Re: Question of the Week - Old Version
Post by: Ians Daddy on 27/10/2003 23:11:16
I know it's layman and probably sounds silly, but my guess is like a military strategy. Like keeping your friends close and your enemies closer. They bond to the antibiotic and learn all they can of it's make up. They record a memory of it and restructure to accomidate it. At that point, they are immune because they are somewhat related. Just like snake venom used as the anti-venom. I really don't know, I just thought I'd take a guess. I figure I've got 50/50 odds of being right or wrong.

Just a thought.
Title: Re: Question of the Week - Old Version
Post by: bezoar on 28/10/2003 04:44:00
Sounds like a layman's description of mutation to me.  Pretty astute. Then too, bacteria like to exchange DNA when they sit together side by side.  I hear it's only a matter of time before we get a Vancomycin resistance staph strain, from exchanging DNA with the Vancomycin resistant enterococcus.  Heard of a couple of scares recently, but no confirmations.  What was thought to be Vancomycin resistant did respond, but only after lengthy treatment.  If anyone has ever read the book The Coming Plague, it'll give you a good scare, but a fascinating book.
Title: Re: Question of the Week - Old Version
Post by: nilmot on 01/11/2003 16:51:02
Change their antigens?

Have caspules so they're hard to engulf?

Just some guesses....

Tom
Title: Re: Question of the Week - Old Version
Post by: Donnah on 02/11/2003 00:59:13
I'm guessing that if we don't finish the course of any antibiotics we take, or if the course is not effective in killing the bacteria then the bacteria learn to recognize the antibiotics (as Ron said) and it's like the bacteria have been vaccinated against the antibiotics.
Title: Re: Question of the Week - Old Version
Post by: cuso4 on 03/11/2003 08:31:38
Each generation of bacteria produces quite fast, so there are always some bacteria survive under the presence of antibiotic. These bacteria then reproduce and create the next generation. This will eventually lead to a mutation in the genes of bateria.

Angel (https://www.thenakedscientists.com/forum/proxy.php?request=http%3A%2F%2Fsmilies.jeeptalk.org%2Fups%2Ficis%2Fices_angel_g.gif&hash=eb252a305c5a566cd34544de7a761914)
Title: Re: Question of the Week - Old Version
Post by: MarkH10178 on 05/11/2003 07:02:14
I was just looking into this one. Those little bacteria are so damn smart - but I forget exactly how they do it. Transposons, something like that. They actually develop the ability to degrade the antibiotic that was meant to knock them off, by producing an enzyme that breaks it up. "Penicillinases" - something like that.

May I suggest a famous question? A while back somebody ran around the Harvard graduation ceremony with a videocam asking these supposedly smartest of all smart kids the question: "Why are there seasons?" - they had the worst time trying to get it right!
Title: Re: Question of the Week - Old Version
Post by: Qing on 07/11/2003 09:50:48
Is the resistance temporary or permanent?Would you feel that if you start using the same antibiotics after quiting for a long time,it becomes effective again? Does that mean the bacteria are not resistant to the antibiotics any more?

Qing
Title: Re: Question of the Week - Old Version
Post by: NakedScientist on 09/11/2003 22:01:23
ANSWER TO THIS WEEK'S "QUESTION OF THE WEEK"

HOW DO BACTERIA BECOME RESISTANT TO ANTIBIOTICS ?

You've all pretty much got the answer right. The mechanism of bacterial anti-microbial resistance comes down to them making a fortuitous mistake when they are copying their DNA.

Because bacteria grow so rapidly they need to copy their DNA rapidly. Occasionally this leads to an error creeping into the genetic code. Most of the time bugs which inherit these errors are at a growth disadvantage because all of the other bugs grow much better than them and hence they are out-competed and disappear.

But if the genetic mistake changes a bacterial protein so that an antibiotic can no long bind on to it, or another enzyme made by the bacterium gains the ability to chew up antibiotics molecules (as well as doing what it did before), now the mutant bacterium has a significant growth advantage whenever that antibiotic is around. All the non-resistant bugs are killed, leaving the resistant bacterium to father a new population of resistant mutants. With all of the competing bugs gone the new mutants enjoy life without any competition - rather like the shrimp fishing in forrest gump !

So the long and the short of it is, the more antibiotics you use, the more resistance you will see. It is a fortuituous mistake on the part of the bacteria. It comes down to the principles of Darwinian natural selection.

TNS
Title: Re: Question of the Week - Old Version
Post by: NakedScientist on 09/11/2003 22:02:35
We liked MarkH's suggestion, so this week's question is :

WHY ARE THERE SEASONS ?

Happy debating,

TNS
Title: Re: Question of the Week - Old Version
Post by: cuso4 on 10/11/2003 13:40:59
The Earth spins on its vertical axis at an angle (I forgot the exact value). As a result, different part of the planet receive different amount(strength) of sunlight creating seasons. This really needs a good diagram to explain properly.

In the summer of a location, the place is slightly closer to the sun and so receive slightly stronger sunlight. In the winter, the place is slightly away from the sunlight so receive slightly weaker sunlight. This also explains why places near the poles have longer daylight in the summer than those near the equator.

As to the changes in the way plants and animals behave also depend on seasons . For example, the hibernation in bears (don't know whether this apply to other hibernating animals or not) is triggered by the change in length of daylight. And people seem to be happier in summer is because seratonine is only produce in sunlight (providing you're not taking anything). This is the substance that stimulates the productiion of noradrenaline.

Angel

"Anyone who has never made a mistake has never tried anything new." -Albert Einstein
Title: Re: Question of the Week - Old Version
Post by: george on 10/11/2003 18:45:54
I take on board what you've said Angel, about the planet being at an angle as it spins, but what makes the seasons change then ? How does the earth alter its degree of tilt; first it tilts one way, closer to the sun for one hemisphere, then the other. How does that happen ?
Title: Re: Question of the Week - Old Version
Post by: UScaV on 11/11/2003 00:10:08
The earth is always tilted at the same angle, which is 23.5 degrees.  The tilt of the earth is always the same and doesn't change.  So as the earth rotates around the sun, the angle changes depending on where the earth is.  That's why it happens at the same time of year each year.  There are 2 equinoxs and 2 solstices a year, and on the winter solstice, the Northern hemisphere is tilted as far away as it possibly can be, and during the summer as close as it possible can be.  Also, twice a year, the the angle to the sun of both hemispheres is the same, and the amount of light and length of day are pretty much equal all over the earth(equinox).

And I don't think winter and summer have to do with the amount of time light is hitting the earth, but rather the distance is has to travel, either fighting it's way through a longer distance and more atmosphere, or a shorter distance and a smaller amount of atmosphere.

Title: Re: Question of the Week - Old Version
Post by: cuso4 on 11/11/2003 08:54:23
George, I think UScaV answered your question. Well explained UScaV.

"Anyone who has never made a mistake has never tried anything new." -Albert Einstein
Title: Re: Question of the Week - Old Version
Post by: george on 11/11/2003 14:02:13
Oh right. I think I've got it now. Thanks for explaining that so clearly !

George
Title: Re: Question of the Week - Old Version
Post by: UScaV on 12/11/2003 04:20:14
I wasn't sure about that last little bit.  Is that one right, where it just has to go through more atmosphere and space?
Title: Re: Question of the Week - Old Version
Post by: tweener on 12/11/2003 04:40:36
Actually, the distance from the earth to Sun is so close to constant year round, that it has nothing to do with temperature.  The difference in seasons is because of the tilt making the light strike at a greater angle (during winter).  This means that for a sunbeam of a given area, there is more surface area for it to cover (and thus less light energy per unit area). The atmosphere is so thin as to make little difference in terms of distance traveled.  

As an example of this, get a flashlight with a narrow beam, shine it straight down.  Then from the same height shine it at an angle (the greater the angle the more pronounced the effect).  You can see that it appears brighter in the straight down configuration and that the beam is covering a smaller area.


----
John
Title: Re: Question of the Week - Old Version
Post by: Quantumcat on 15/11/2003 08:39:34
Also, the part of the earth tilted toward the sun is closer, so the heat has dissapitated less by the time it gets there and it's warmer. There's longer days in summer because the part of the earth you're on gets a wider light spread (if you've ever seen a Geochrome [is that what they're called? I can't remember] then you'll know what I mean.)

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Title: Re: Question of the Week - Old Version
Post by: NakedScientist on 17/11/2003 17:57:07
Quantum - if you do want to discuss things related to QOTW then please feel free to start a new thread in a relevant section of the forum.

TNS
Title: Re: Question of the Week - Old Version
Post by: NakedScientist on 17/11/2003 18:06:01
I think the issue of why we have seasons has been explained better than we could have done, so no further comment from us needed...

Anyway here is this week's QOTW (Question of the Week) :

"WHAT HAPPENS IF YOU LIGHT A MATCH INSIDE A SPACESHIP WHILST IT IS IN SPACE ?"

Have a go, below. Please remember that we love questions to come from you guys, so please put forward suggestions for future questions via this email address : qotw@thenakedscientists.com (http://mailto:qotw@thenakedscientists.com)

TNS
Title: Re: Question of the Week - Old Version
Post by: Ians Daddy on 17/11/2003 19:01:16
KABOOM!!!
Title: Re: Question of the Week - Old Version
Post by: Quantumcat on 18/11/2003 08:02:45
I remember learning about flames in low gravity, I can't remember completely. It looks like a demi sphere, and it's a different colour.

I have a theory of how flames work, but no one has ever told me the real way they work. Perhaps you guys can tell me. My theory is that the heat gives the atoms energy to leap off the wood, they emit light as they go then fall back to earth as ash. Different atoms jump different heights, atoms that emit blue light don't jump as high as atoms that emit yellow light (carbon right?) but they jump higher than green light-emitting atoms. Sparks are lumps of atoms who couldn't prise themselves apart but emit light all together all the same. Because they're larger they get to jump higher than other atoms of the same kind that aren't sparks, because the breeze catches them. Coals glow because the heat has constricted them, they are too big to be carried up by the breeze and the atoms can't jump off them, so the atoms just emit their light without moving. There is considerably less matter when the fire is done because a lot of it was changed by a chemical equation into heat (I learned that at school, didn't make it up lol) the ash is all the light-emitting atoms and the chunks of black stuff were the coals. If anyone knows how it really works I would like to know. Thanks.

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Title: Re: Question of the Week - Old Version
Post by: tweener on 18/11/2003 15:30:12
Ronnie might be right if the spacecraft has pure oxygen for an atmosphere, but I think after Apollo 1 most people know better.

I believe that the flame would make a sphere (or close to it) around the head of the match.  It would keep increasing in radius while it burned, but it would not burn long.

This behavior is due to the lack of gravity causing there to be no density gradient in the air.  In a gravity field, the air is always more dense the lower you go.  When it is heated, or a hot gas is introduced, the hot gas is less dense than the surrounding air, and thus floats upward.  If there is no density gradient, then it does not float, it just stays put.  In the case of the match, the chemical reaction of burning is releasing hot gases from the wood, and thus the "flame" is going to keep increasing until the match burns out.  The match would stop burning quickly because there is no fresh air (oxygen) reaching it (it is surrounded by its own gases).


----
John
Title: Re: Question of the Week - Old Version
Post by: NakedScientist on 26/11/2003 11:05:43
ANSWER TO LAST WEEK'S QUESTION OF THE WEEK "What happens if you light a match inside a spacecraft orbiting the earth ?"

This question concerned the early pioneers of space travel a great deal. But tests showed that flames just don't work in space - to understand why not you have to first consider what a flame actually comprises.

Flames always point upwards. That's because gravity creates a density gradient in the air so that hot air, which is less dense, rises whilst cold air sinks. This is why a hot-air balloon can float.

So when something burns the hot vapourised fuel (which is rising) pulls in cold fresh air from the bottom (containing oxygen) which oxidises the fuel and creates more flame and heat. The heated vapours rise and so the process continues.

But in space, under 'weightless' conditions, there is no density gradient in the air because there is no up or down ! This means that when you try to burn something, the vapours cannot rise away and so the fire suffocates itself because fresh air (oxygen) cannot gain access to the fuel sufficiently quickly.

So, unlike Ian's Daddy's suggestion "kaboom", the more likely outcome would be something like "phutt".

TNS
Title: Re: Question of the Week - Old Version
Post by: NakedScientist on 26/11/2003 11:08:02
HERE IS THIS WEEK'S Q-O-T-W :

"WHY DOES HELIUM MAKE YOUR VOICE SOUND FUNNY ?"

Have a go, below :

TNS
Title: Re: Question of the Week - Old Version
Post by: cuso4 on 26/11/2003 14:02:06
This is a guess.

We make sound by making the air vibrate. Since helium is much lighter than air so when we speak, same amount of energy will make helium gas vibrate much more. Higher frequency of sound is produced and so the voice sounds funny.

"Anyone who has never made a mistake has never tried anything new." -Albert Einstein
Title: Re: Question of the Week - Old Version
Post by: Quantumcat on 26/11/2003 16:25:36
That's exactly what I would have said, hopefully we are right

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Title: Re: Question of the Week - Old Version
Post by: nilmot on 27/11/2003 12:38:46
Mmm... interesting suggestion.

So If I inhale lighter air e.g. Hydrogen, would that make my voice go funny as well?

Tom
Title: Re: Question of the Week - Old Version
Post by: chris on 27/11/2003 16:19:52
If you're going to do the experiment, I wouldn;t smoke afterwards !

"I never forget a face, but in your case I'll make an exception"
 - Groucho Marx
Title: Re: Question of the Week - Old Version
Post by: nilmot on 28/11/2003 08:31:49
KABOOM!!!! [:D]

P.S I don't smoke anyway Chris.. [:)]

Tom
Title: Re: Question of the Week - Old Version
Post by: NakedScientist on 04/12/2003 14:48:34
Here is the answer to last week's QOTW - "WHY DOES HELIUM MAKE YOUR VOICE GO FUNNY ?"

Most of you are on the right lines :

If you imagine your throat as a bit like an organ pipe, when the organist plays a note, one cycle of a wave, with a wavelength approximately the length of the tube, is generated inside the pipe. So when you talk you produce sound waves with wavelengths determined by the length of your throat.

The speed of a wave (c) is given by multiplying the wavelength and the frequency together (c=l.f) and this can be re-arranged to find the frequency of the sound wave (in other words how high it sounds) (f), thus : "frequency = speed divided by wavelength" or f=c/l.

But helium is less dense than the other consitutents of air and so sound travels much more quickly in helium (900 metres per second) than in air (350 metres per second). Substitute these numbers into the forumla we got above (f=c/l) and you get a value for f (helium) 2.5 times greater than f (air). As a result you voice sounds 2.5 times higher when you breathe helium.

Conversely, if you were to breathe a denser gas than air you could make your voice sound much lower.

Divers breathing a helium-rich mix (to overcome the problem of increased gas density at extreme depths) talk to their support crew using a "helium voice unscrambler" which reinforces the lower notes in their voices whilst suppressing the higher tones so that they can be understood.

TNS
Title: Re: Question of the Week - Old Version
Post by: NakedScientist on 04/12/2003 14:51:51
This week's QOTW was submitted by Tom :

"WHEN WE SAY ARSENIC / MERCURY / CYANID ARE POISONOUS, WHY ARE THEY POISONOUS ? "

Over to you !

TNS
Title: Re: Question of the Week - Old Version
Post by: Donnah on 04/12/2003 19:06:02
For mercury:

-vaporizes slightly at room temperature
-vapor is odorless/colorless/extremely toxic
-cumulative poison
-crosses blood/brain barrier
-accumulates in brain's pain centre and central nervous system
-prevents normal entry of nutrients into cells
-prevents removal of wastes from cells
-binds to immune cells and impairs function

I'd like to see the biology and chemistry wizards give a more technical view.

Now for my own rant.

Mercury
-is sometimes a component in innoculations (thermisol)
-trivalent innoculations (DPT, MMR) sometimes cause autism
-normally comprises more that 50% of amalgam (silver) dental fillings
-duh!!!!
Title: Re: Question of the Week - Old Version
Post by: cuso4 on 05/12/2003 13:46:38
Yay, just glad that me and quantum got the helium question correct. Right here goes my answer:

The three substances work similarly. They all affect the electron transport chain (also called oxidative phosphorylation) of cellular respiration. If a cell cannot make ATP, the cell will die.

Arsenic, mercury and cyanide all can inhibit mitichondrial enzyme so that the normal substrate cannot bind. A vital reaction in the process will stop and disrupt the respiration. In the case of cyanide, it inhibits the enzyme cytochrome oxidase.

Furthermore, cyanide and carbon monoxide are respiratory inhibitors which can bind permenantly to haemoglobin preventing it bind with oxygen. This explains why a poinsoned person get breathless. If exposed to large dose, the person can soffocate and die.

Angel

"Anyone who has never made a mistake has never tried anything new." -Albert Einstein
Title: Re: Question of the Week - Old Version
Post by: nilmot on 06/12/2003 09:44:21
Ooh, we are getting some pretty good answers here.

And also thanks TNS, for putting my question on the forum.[:)]

Tom
Title: Re: Question of the Week - Old Version
Post by: NakedScientist on 05/01/2004 11:56:17
HAPPY NEW YEAR EVERYBODY.

HERE'S THE FIRST QOTW FOR 2004, SENT IN BY PAUL SANDKUIJL.

"When you are woken up by a sound and that exact same sound was part
of your dreams ie. the alarm clock, did you begin dreaming your dream
as a result of the sound or were you already dreaming and that sound
became part of your dream?"

DOES ANYONE ELSE EXPERIENCE THIS, AND IF SO, WHY ?

TNS
Title: Re: Question of the Week - Old Version
Post by: bezoar on 05/01/2004 15:12:33
Yes, I've had it too, and I always thought the noise triggered the dream.  What was stranger is that when my girls were babies, I always woke up before they did at night, and I would lie still and try to go back to sleep, and invariably they woke up too.  I was never sure if I awakened because I knew they were about to, or if they awakened because they sensed I was awake.

Bezoar
Title: Re: Question of the Week - Old Version
Post by: tweener on 05/01/2004 20:20:55
I incorporate external sounds into my dreams all the time.  I think the sound is incorporated, but sometimes it seems the other way around.  Once a dream took it to an extreme:  The alarm was beeping, and I turned it off.  But it wouldn't quit beeping, so I banged the clock on the nightstand.  Then I unplugged it, and it still kept beeping.  Then I removed the cover and started tearing components from the board, and it still kept beeping.  Finally, I had it stripped down to a single little "box" that was beeping, with no apparent power source.  I was really tired by the time I finally came awake.

Nancy,
Babies are very sensitive to their parent's breathing and emotional status, even when they are asleep, so I think they probably woke up because you were awake.  Also, you may have awakened because they changed their breathing pattern before waking, so it may have been a "feedback" scenario.  It is amazing how aware we are even when asleep.


----
John
Title: Re: Question of the Week - Old Version
Post by: bezoar on 11/01/2004 03:42:28
Can they sense your breathing changes from another room?  If so, that would explain why my kids didn't begin sleeping all night until they were about 12 or 13.  I'm not much of a sleeper and awaken frequently during the night.  It would be interesting to study if babies who sleep all night long from the time they come home from the hospital have mother's who are heavy sleepers.

Bezoar
Title: Re: Question of the Week - Old Version
Post by: NakedScientist on 15/01/2004 18:04:22
This was quite a tough question.

The answer probably lies in the fact that dreaming occurs when you are in a state of near-wakefulness. Events from the environment can therefore intrude into your dream and even participate in it. Everyone must have experienced the hilarious situation of talking to someone who is asleep. They have no recollection afterwards of what was said, unless they wake up mid conversation.

As to why you wake up and then hear the alarm, giving the impression that you pre-empted the alarm clock, I think there are many possible explanations. You could geuninely have woken up before the alarm because your body-clock has become accustomed to you getting up at that time that it woke you up automically. Alternatively, and this is the explanation I favour, you were dreaming when the alarm went off. In that split second the alarm got incorporated into your dream. As our sense of time is totally skewed when we dream you have no concept of when you really woke up, and when the alarm really started going off.

A hard nut to crack, but still a great question.

TNS
Title: Re: Question of the Week - Old Version
Post by: NakedScientist on 15/01/2004 18:05:48
THIS WEEK'S QOTW :

"IF ALL THE PASSENGERS ON AN AEROPLANE SUDDENLY JUMPED INTO THE AIR AT THE SAME TIME, WOULD THE PLANE MOMENTARILY WEIGH LESS ?"

Have a go, below :

TNS
Title: Re: Question of the Week - Old Version
Post by: Quantumcat on 16/01/2004 07:42:18
That's just like a question that was on this old maths competition thing. the question was, there's a guy that's a juggler that wants to cross a bridge that can only hold a certain weight, and him and the bazlls weigh over it but him and one ball is enough to get by, the question was if he always has two balls in the air can he cross safely.

It does sound like one of those questions, I know the nswer is that it would weight exactly the same, but I'm not exactly sure why. Well the passengers are not 'the plane' so the plane would weigh the same, but I don't think that's really the issue. hmm. I'm sure it has a lot to do with the diagrams of vectors pointing all over the place that my physics teacher just loves drawing. I can just imagine one now ... there's be P pointing downwards from the middle of the plane, something pointing upwards for the thing that keeps the airplane up, lots of P's for the passengers' weights, and lots of R's pointing up for the reaction de support. But come to think of it, if you say 'would the plane momentarily weigh less" you probably mean the plane and the passengers' weights combined right? So on the ground it'd be the same but instead of the vector for the thing that keeps the plane in the air there'd be a big R for the reaction de support of the ground. and when the passengers jump, they'd have to, like, push on the plane a lot to get themselves up off the floor, so the diagram with them pushing off would be a vector pushing down for each, a vector pushing up that would carry them up, their weight, and their reaction de support. The diagram with them in the air would be with their weight and the vector pushing them up then on the way to the ground it would be just their weight. When they're on the floor just as they jump I suppose their reaction de support's would be bigger than before they pushed off. So, in conclusion, I suppose the combined weight would be bigger as they pushed off (but the R's bigger so the plane doesn't, like, move underground or whatever) then the P would just be of the plane, then when they land it'd be the same again except maybe that the landing of the passengers would induce some movement of the plane and make the combined weight go up again for a short time until the movement of the passengers towards the earth had stopped, by the R's going upwards?

I don't know if that's how it's meant to be answerd but that's just a try.

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Title: Re: Question of the Week - Old Version
Post by: cuso4 on 16/01/2004 08:42:27
At the instant when all the feet of the passengers leave the floor of the aeroplane, the overall reaction  should decrease but then all the passengers are still experiencing gravitational pull so the overall weight shouldn't change.

Not the most straight forward question, I'll have to think about it again.

Angel

"The people who will succeed are those who see the invisible and do the impossible."
Title: Re: Question of the Week - Old Version
Post by: Quantumcat on 16/01/2004 15:02:31
what do you mean by 'the overall reaction will decrease'? with the gravitational pull, it's giving them acceleration back towards the plane, but it is only applied to the passengers while they're in the air, not to the plane right? Please tell us the answer NS!

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Title: Re: Question of the Week - Old Version
Post by: tweener on 16/01/2004 19:45:28
Last night I wrote a long response to this and my computer crashed before I got it submitted.  Here is a short version.

The average weight of the plane and passengers, averaged over the whole "jump" would remain constant.  On a finer timescale: The weight would start as the combined weight of the plane and passengers. Then, as they jumped, the "weight" would increase to accelerate them upward.  While they were off the floor of the plane the weight would decrease to just the weight of the plane. Then, when they hit the floor of the plane the weight would again increase a lot to decelerate them. Finally, the weight would come back to the "normal" weight of the plane and passengers after they got back to the floor.


----
John
Title: Re: Question of the Week - Old Version
Post by: Quantumcat on 17/01/2004 08:58:00
whoo!

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Title: Re: Question of the Week - Old Version
Post by: notnakeeinappalachee on 21/01/2004 14:57:15
The plane weighs the same.  The weight of the plane plus its contents, however, is greater when its contents are in contact with its floor.  

Title: Re: Question of the Week - Old Version
Post by: chris on 21/01/2004 16:54:42
But what about the fact that the plane is sealed (pressurised) - does this make a difference ?

Chris

"I never forget a face, but in your case I'll make an exception"
 - Groucho Marx
Title: Re: Question of the Week - Old Version
Post by: bezoar on 22/01/2004 21:58:17
Shouldn't the pressurization of the plane, in itself, increase the weight?
Title: Re: Question of the Week - Old Version
Post by: tweener on 23/01/2004 05:24:34
The overpressure of the air would increase the weight a little.  Probably a few milligrams for the amount of pressure in a plane.  Of course it depends on the size of the plane.


----
John
Title: Re: Question of the Week - Old Version
Post by: NakedScientist on 26/01/2004 12:42:03
ANSWER TO "WHAT HAPPENS TO THE WEIGHT OF A PLANE IF ALL OF THE PASSENGERS JUMP INTO THE AIR SIMULTANEOUSLY ?"

This was a tough one. Tweener's answer is correct in that in order to accelerate themselves off the floor of the plane the passengers must apply a force and hence the plane will transiently increase in weight. Whilst the passengers are airbourne their weight is no longer pushing down on the plane so it rebounds upwards. Then as they land again their weight is added to that of the plane and the total masss returns to the starting value.

TNS
Title: Re: Question of the Week - Old Version
Post by: NakedScientist on 26/01/2004 13:26:21
Here's this weeks QOTW :

"HOW FAST IS THE EARTH SPINNING ON ITS AXIS ? HAS IT ALWAYS TURNED THIS FAST ?"

TNS
Title: Re: Question of the Week - Old Version
Post by: Quantumcat on 26/01/2004 15:11:25
I have no idea how fast, but I remember the teacher saying in astronomy three years ago that it spun really fast when it was formed and is slowing down.

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Title: Re: Question of the Week - Old Version
Post by: Quantumcat on 26/01/2004 15:12:09
I have no idea how fast, but I remember the teacher saying in astronomy three years ago that it spun really fast when it was formed and is slowing down.

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Title: Re: Question of the Week - Old Version
Post by: Donnah on 26/01/2004 20:54:00
According to Gregg Braden the earth's magnetics are decreasing and frequency is increasing.

Not sure about how fast the earth is spinning, but guess you could work it out using the circumference of the planet and a 24 hour time period.
Title: Re: Question of the Week - Old Version
Post by: roberth on 27/01/2004 02:31:00
Earth currently rotates at about 1,609 km/h. I don't know if this is constant.
Title: Re: Question of the Week - Old Version
Post by: notnakeeinappalachee on 27/01/2004 16:40:38
Pertaining to the last question--weight is due to gravity, which is the force of attraction exerted by the mass of two bodies.  In the case of the airplane, the two bodies are the plane and the earth.  The slight increase in earthward force (and acceleration) exerted when the people push downward in order to jump is not due to the pull exerted by earth and therefore is not an element in the plane's weight.  

Never was much for angular momentum and its relatives.
Title: Re: Question of the Week - Old Version
Post by: chris on 27/01/2004 22:53:37
I think that's what they are getting at by referring to "pedants" - it is assumed for the sake of simplicity that the word "plane" refers to the entire system i.e. the plane, the air it contains, and the passengers.

Anyway, what abou this earth rotation question ?

Chris

"I never forget a face, but in your case I'll make an exception"
 - Groucho Marx
Title: Re: Question of the Week - Old Version
Post by: bezoar on 28/01/2004 02:52:20
How fast the earth spins might depend on where on earth you are.
Title: Re: Question of the Week - Old Version
Post by: roberth on 29/01/2004 00:33:01
OK, then, 1,609 km/h at the equator.
Title: Re: Question of the Week - Old Version
Post by: pipster on 02/02/2004 14:57:22
The earth and all the other planets in the solar system are spinning because of the resultant angular momentum from their formation billions of years ago. As the clouds of dust and gas came together under gravity, the matter they contained was pulled in closer and closer until finally the planet we now live on was formed.
Just as when an ice skater spinning on the spot goes faster when they pull their arms in (try it on a swivel chair) this gas contraction increased the angular momentum that causes our days and nights to come round every 12 hours (at the equinox).

Like all systems, energy is lost over time (like a pendulum eventually comes to rest vertically) and so the rotation about our axis is decreasing. This will eventually increase the length of the day since more time will be spent in or out of sunlight at anytime.

Velocity of rotation of a point about an axis (in this case angular momentum) = 2xpixr/24hours
At the north pole where the distance to the centre of rotation could be close to zero, you will have zero angular momentum and it increases up to the equator.

IF the earth spinning around on its axis slows down enough, days will get longer and longer and eventually the length of a day might over take the length of the year, which I believe is what has happened to Mercury?
Title: Re: Question of the Week - Old Version
Post by: Ultima on 06/02/2004 12:54:21
The Earth wobbles on its axis wouldn't this effect the speed a tiny bit?
Title: Re: Question of the Week - Old Version
Post by: roberth on 09/02/2004 00:25:15
C'mon TNS. You should rename this topic "question of the fortnight".
Title: Re: Question of the Week - Old Version
Post by: neilep on 09/02/2004 15:57:25
As a kid, I used to think the wind was caused by the Earth spinning faster that day !!!!....

'Men are the same as women...just inside out !'
Title: Re: Question of the Week - Old Version
Post by: Quantumcat on 11/02/2004 15:21:43
Lol!! That's so cute! I remember thinking it was caused by convection before I learnt about pressure and stuff.

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Title: Re: Question of the Week - Old Version
Post by: NakedScientist on 21/02/2004 07:33:38
Answer to HOW FAST IS THE EARTH SPINNING ? IS THE RATE CHANGING ?

The earth completes 1 revolution per day (24 hours). The distance that it effectively travels (at the equator) in completing 1 revolution is equal to the planet's circumference or girth.

You can calculate the circumference of a circle using the formula 2x pi x radius of the circle.

The radius of the earth is 3963 miles (6378 kilometres). The circumference is therefore 2 x 3963 x 3.141 (approx. value of pi) = 24900 miles (40,000 km)

The speed of the earth is therefore 24900 / 24 = about 1000 miles per hour (1600 km per hour).

The rate of rotation is indeed slowing down. About 65 million years ago, at the time of the dinosaurs, the earth span much more quickly meaning that a day was correspondingly shorter, lasting only about 16 hours.

It is worth bearing in mind, however, that the calculation above applies at the equator - the actual speed you would be travelling at varies according to where you stand on the planet surface - at the north pole, for instance, your speed would be zero. In the UK and north US your speed is closer to 700 - 900 miles per hour (1125-1450 kilometres per hour).

sorry this took a little while to come out - I've been a bit busy !

TNS
Title: Re: Question of the Week - Old Version
Post by: NakedScientist on 21/02/2004 09:01:49
Here's this week's QOTW :

"WHAT IS A SUNSPOT ? WHAT CAUSES THEM AND WHAT EFFECTS CAN THEY HAVE UPON EARTH ?"

TNS
Title: Re: Question of the Week - Old Version
Post by: cuso4 on 24/02/2004 08:39:11
Astronomy is never my strong point. I'll have to do some research for this.

Angel

"The people who will succeed are those who see the invisible and do the impossible."
Title: Re: Question of the Week - Old Version
Post by: CsManiacDan on 29/02/2004 20:32:37
I'm pretty sure a sun spot is an area on the sun that's cooler than the rest of it, that's why it's darker, though why it's cooler i have know idea nor do I know whats causing it

I Love Caesium!!!
Title: Re: Question of the Week - Old Version
Post by: neilep on 29/02/2004 21:17:28
Yep...Im with you on that one Dan, I'm sure magnetism comes into the equation too somewhere along the line, as well as the eleven year cycle, where they pop up the most and last about a week or so. Not too sure what effects they have upon the earth apart from manifestations arising from magnetic disruptions ? perhaps electrical disruption and interference with satellite communications, and birds/sealife/animals that depend on the earths magnetic field for navigation.

Or is it just something that adolescent stars get as they go through puberty ? :-)


'Men are the same as women...just inside out !'
Title: Re: Question of the Week - Old Version
Post by: Donnah on 02/03/2004 04:07:20
I vaguely remember hearing something about sun spots and radioactivity.
Title: Re: Question of the Week - Old Version
Post by: NakedScientist on 02/03/2004 05:48:55
ANSWER TO LAST WEEK'S QOTW "WHAT ARE SUNSPOTS AND HOW DO THEY AFFECT THE EARTH ?"

Sunspots are dark spots, up to 50,000 miles in diameter, that move across the surface of the sun, expanding and contracting as they go. They usually last for several days, although very large ones can persist for several weeks.

A typical sunspot comprises a dark region called the umbra, surrounded by a lighter region known as the penumbra. They appear relatively dark because the surrounding surface of the Sun (called the photosphere) is about 5500 degrees C., while the umbra is a chillier 3480 degrees C.

Sunspots are surrounded by an intense magnetic field over 2,500 times stronger than Earth's, which is much higher than anywhere else on the Sun. This powerful magnetic field slows down the flow of hot gases from the Sun's interior to the surface, which is why sunspots are relatively cooler than the rest of the sun's surface. They usually occur in pairs which have their magnetic fields pointing in opposite directions

People have been watching sun spots since Galileo Galilei first described them in the early 1600s, and we probably knew about them even before that. There are reports of ancient peoples noticing the sun's blemished appearence, particularly on cloudy days and during dust storms.

But thanks to Galileo's work we now know that the sun follows an 11 year cycle - the Solar Cycle - during which the number of sunspots steadily increases to a maximum, then decreases again at the end of the cycle. Towards the maximum the sunspots occur closer to the equator of the Sun. Plotting the area covered by sunspots at a given latitude versus time produces an interesting butterfly shaped distribution of unknown significance.

Some studies have suggested that the average ocean temperature increases and decreases, world-wide, by 0.5 degrees C in phase with the sun spot cycle, but the mechanism is not understood.

So how do sunspots affect the earth ?

This is not known for certain. During periods of maximum sunspot activity scientists have recorded a very slight increase in the energy output from the sun, and ultraviolet (UV) radiation increases dramatically which can affect our atmosphere. Also, a period known as known as the Maunder Minimum, during which there were very few sunspots, coincided with a number of long winters and severe cold temperatures (called the Little Ice Age) in Western Europe.

Furthermore, sunspots are also associated with phenomena called CME - Coronal Mass Ejections or solar flares. These stellar convulsions produce as much energy as a billion megatons of TNT and occur near to sunspots on the dividing line between the pair of oppositely directed magnetic fields. Solar plasma interacting with the strong magnetic field is ejected away from the sun's surface and out into space forming the flare which bathe the earth in cosmic radiation leading to an increase in geomagnetic storms which can affect satellites, power grids and radio transmissions. They also produce a more pleasant side effect - the beautiful northern and southern lights - where the charged particles interact with the earth's magnetic field...

Some sunspots :

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Title: Re: Question of the Week - Old Version
Post by: NakedScientist on 03/03/2004 02:13:05
Here is this week's question of the week :

"CAN YOU EXPLAIN 'WIND CHILL FACTOR'" ?

TNS
Title: Re: Question of the Week - Old Version
Post by: Quantumcat on 03/03/2004 09:17:59
I think so. Wind chill factor is when lots of bits of moisture in the air go past your skin fast, taking heat as they go. Or maybe it's not moisture it's air. Oh well, doesn't matter. That's why you're cold when you get out of the bath too, because the water becomes a thin layer and the abundant heat in your skin goes into the water and it evaporates. All the heat moving out of you makes you feel cold. Also why fans that push air around make you lose heat and feel cooler.

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Title: Re: Question of the Week - Old Version
Post by: BlooGoo on 11/03/2004 19:40:29
I think I have to agree with Quantumcat, but I'm not sure if it's moisture in the air, or air molecules themselves, that cause the decrease in temperature, because (I think) it's possible to have a windchill when there's very little moisture in the air.

Just my 2 cents.
Title: Re: Question of the Week - Old Version
Post by: tweener on 11/03/2004 20:35:42
Moisture in the air (aka relative humidity) affects the wind chill factor by making the air capable of holding more heat for a given volume.  At the boundary between skin and air, there is a layer of still air that warms up and serves to insulate the skin from losing more heat.  When wind moves the air, this layer is thinned and cooled, thus increasing the rate  of heat loss.  The faster the wind blows the faster the heat is lost, thus the wind chill temp. is lower.  The higher the relative humidity, the more efficiently the air removes heat from the skin, and the lower the wind chill temp.

Sounds good anyway.

----
John - The Eternal Pessimist.
Title: Re: Question of the Week - Old Version
Post by: NakedScientist on 14/03/2004 02:00:21
ANSWER TO LAST WEEK'S QOTW "CAN YOU EXPLAIN 'WIND CHILL FACTOR'"

You have all pretty much hit the nail on the head. Heat leaves our bodies, which are much warmer than the surroundings, by following a thermal gradient (hot to cold). The cooler the surroundings relative to body temperature, the steeper the gradient and hence the greater the rate of heat loss.

When you stand in still air, heat leaving your body warms the air around you so that it acts like a layer of insulation. This effectively reduces the thermal gradient, slowing down heat loss. But when you are out in a high wind the air around your body is continuously being replaced with fresh cold air. Under these circumstances the thermal gradient becomes much steeper and you lose heat much more rapidly, at a rate equivalent to the surrounding temperature being much colder than it really is. Hence the term "wind chill factor".

TNS
Title: Re: Question of the Week - Old Version
Post by: NakedScientist on 14/03/2004 02:01:34
This week's QOTW is much more challenging and might require a bit of research on your part, but has a satisfying answer. Have a go at :

"WHY ARE THERE 7 DAYS IN A WEEK, AND WHY DOES THE WEEK BEGIN ON A MONDAY ?"

Happy hunting

TNS
Title: Re: Question of the Week - Old Version
Post by: nilmot on 15/03/2004 08:27:56
I'm not so sure this is a scientific question. More of a philosophical question.

Tom
Title: Re: Question of the Week - Old Version
Post by: NakedScientist on 15/03/2004 23:04:58
No, it is definitely a scientific question, with a scientific answer, though some of the answer has its origins in philosophy.

TNS
Title: Re: Question of the Week - Old Version
Post by: cuso4 on 17/03/2004 13:40:39
I found something on the Internet which might be what we're looking for.

Why are there 7 days in a week?

One month is roughly the time taken for the Moon to rotate the Earth once. One year is 365 days and divide this by 12, we get 30.416 days per month. One week is the time taken for the Moon the a quarter of the Earth. So divide 30.416 by 4, we get a value around 7.

I'm not sure anout the second question but I'll have a go.
Monday is named after the Moon and since ancient people use the movement of the Moon to measure time (Chinese Calender is based on this), Monday is set to be the first day of the week.

Angel
Title: Re: Question of the Week - Old Version
Post by: NakedScientist on 19/03/2004 05:19:39
Well done Angel, you are on the right lines. Keep going.

TNS
Title: Re: Question of the Week - Old Version
Post by: neilep on 19/03/2004 13:32:48
Here is something I have blatantly 'borrowed' from a website I found which I think part explains why Monday is the first day of the week.

MONDAY
There are some countries which have Monday as the first day of the week. This is in accordance with the International Standard
"ISO 8601:1988 (E)"
Which states under item:
5.4 Combinations of date and time of day representations
3.0 Terms and Definitions
3.17 Week Calendar
"A seven day period within a calendar year,
starting on Monday and identified
by the ordinal number with in a year....."

There are countries in Europe, such as Denmark, Norway and Sweden that have Monday as the first day of the week.
In the USA documents ANSI (X3.30) and NIST (FIPS 4-1) adopted ISO 8601 and list Monday as the first day of the week.
However, the calendar in USA has
Sunday as the first day of the week


'Men are the same as women...just inside out !'
Title: Re: Question of the Week - Old Version
Post by: neilep on 19/03/2004 13:37:32
Here is something else i have borrowed, regarding the number of days in the week.
Known as an interval between Market Days. In central Asia five days was used, Egyptians used ten days and the Babylonians like the multiple of seven because of the lunations of the moon. In Rome the eight day cycle was used for market. The orgin of the seven day week seems to be related to the four (about) seven day phases of the moon. Also the seven colors in the rainbow, and in the Babylonian times, the seven planets. By the time of the first century BC the Jewish seven-day week seems to have been put into place throughout Rome.


The calendar in the USA has Sunday as the first day of the week. The word week comes from Latin "vicis" meaning change. The week is a period of seven days and is now used throughout the world as a division of time. History seems to favor the Hebrew or Chaldean origin and the week is mentioned as a unit of time in the Bible, see the Old Testament book of Genesis 29:27.
....do me and Angel get a gold star ?

'Men are the same as women...just inside out !'
Title: Re: Question of the Week - Old Version
Post by: tweener on 19/03/2004 16:13:09
If you're going to insist that Monday is the first day of the week despite every calendar in the known universe, then I say Monday is the first day of the week so that everyone can get off to a really rough start every seven days. [:)]

----
John - The Eternal Pessimist.
Title: Re: Question of the Week - Old Version
Post by: neilep on 19/03/2004 17:06:54
Personally..I think Mondays should be cancelled [:D]

'Men are the same as women...just inside out !'
Title: Re: Question of the Week - Old Version
Post by: Donnah on 19/03/2004 21:16:12
I've got it!  It's divine intervention that caused the 7 day week and the week to begin with Monday.  We're told that God made the world in six days and took the 7th day to rest, calling it the sabath.  How do you like that?  He takes the 7th day to rest but expects us to get up on that day to go to church.  *tongue in cheek*
Title: Re: Question of the Week - Old Version
Post by: nilmot on 20/03/2004 08:45:27
But isn't that a religious explaination not a scientific explaination?

Tom
Title: Re: Question of the Week - Old Version
Post by: tweener on 21/03/2004 18:28:35
I vote for cancelling Mondays.  But everytime I try, Tuesday is worse than Monday.

----
John - The Eternal Pessimist.
Title: Re: Question of the Week - Old Version
Post by: Boffy Clywd on 25/03/2004 16:54:03
quote:
Originally posted by NakedScientist

HERE'S THE ANSWER TO LAST WEEK'S "QUESTION OF THE WEEK", SUBMITTED BY NILMOT (Tom Lin)

The appearence of the moon in the sky depends upon the position of its orbit. There is no reason why the moon and sun should not appear together in the sky since they are totally independent of each other. The moon orbits the earth and the earth orbits the sun. Therefore sometimes the moon coincide on its orbit with the rising of he sun and hence the two will appear in the sky together.

This is precisely how an eclipse occurs, only on this occcasion the path of the moon crosses the path of the sun. But the two bodies are still in the sky at the same time.

I think most people seemed to get that one right. Good question though. By an amazing co-incidence a lady phoned the radio show a few weeks ago with the same question !

Title: Re: Question of the Week - Old Version
Post by: Boffy Clywd on 25/03/2004 17:00:22
The moon and sun do not very often appear near each other in the sky for a very good reason. The sun is so bright, and back lights the moon, that it can not be seen even though it is often there. Just before and after any eclipse the moon is not visable for example. Often the moon can be seen if it is over the other side of the sky from the sun, this will mean the distance from the moon to the sun is greater than the distance of the earth to the sun.
  [8D]
Title: Re: Question of the Week - Old Version
Post by: NakedScientist on 05/04/2004 09:47:30
Here's the answer to the last QOTW "WHY ARE THERE 7 DAYS IN A WEEK, AND WHY DO WE HAVE TO HAVE MONDAYS ?"

It all comes down to the ancient Greeks, Romans and Babylonians.

Early observers of the sky saw several prominent features - the Sun, the Moon, and the stars. But closer inspection of the stars showed that whilst most moved across the sky in a uniform way, some moved at different speeds and even turned back on themselves. These errant stars were named 'wanderers' which in ancient Greek is planetes, from which we get our modern word "planet". At that time early observers only found 5 'planetes' (Mars, Jupiter, Saturn, Mercury and Venus) - the discovery of the rest would have to wait for the telescope to come along.

Observations on these 'planets' showed that they take a different amount of time to complete a cycle and return to their starting position. The planets were assigned a seniority according to how long they took to complete their own cycle :

Saturn 29 years
Jupiter 12 years
Mars 687 days
Sun 365 days
Venus 225 days
Mercury 88 days
Moon 28 days

The Babylonians decided to divide a day into 24 hours (in place of the 12 used by Egyptians) and decided to name each hour of the day after each of the 'planets' in order of seniority, and startign again when you run out of planets. e.g. :

1 am - Saturn
2 am - Jupiter
3 am - Mars
4 am - Sun
5 am - Venus
6 am - Mercury
7 am - Moon ...and start again with...
8 am - Saturn
9 am - Jupiter and so on...
...10 pm Saturn
...11 pm Jupiter
...12 pm Mars

Obviously 7 doesn't divide equally into 24 so the next day starts with a new 'dominant planet' (the one at the top of the list). It was the custom to name the day after the dominant planet on that day.

Looking on the list you can see that after Mars comes "Sun" and hence the next day starts with Sun and works through the list. The day after that starts with "Moon", then "Mars", then "Mercury", then "Jupiter", then Venus and finally back to Saturn.

If you then write out these dominant planets in order you see a familiar pattern emerge :

Planet       English   French

Saturn day   Saturday  Samedi
Sun Day      Sunday    Dimanche
Moon Day     Monday    Lundi
Mars Day     Tuesday   Mardi
Mercury Day  Wednesday Mercredi
Jupiter Day  Thursday  Jeudi
Venus Day    Friday    Vendredi

This 7 day week was adopted by the Romans who spread it across their empire. The Pagan English preferred to keep Sunday for the Sun God, and also named the previous 4 days of the week after Anglo-Saxon gods - Tiw (Tuesday), Woden (Wednesday), Thor (Thursday) and Frig (Friday). The Christians wanted a different holy day to the Jews - so they took Sunday (Dimanche) which is a contraction of Dies Dominici (Day of our Lord) in Latin). Because Sunday is the Christian day of rest, we have to have Monday mornings on which to return to work...ouch.

Title: Re: Question of the Week - Old Version
Post by: NakedScientist on 05/04/2004 09:53:31
Here is this week's QOTW :

"IF A CAR IS DRIVING AT THE SPEED OF LIGHT AND IT TURNS ON ITS HEADLIGHTS, WILL THE WAY AHEAD BE ILLUMINATED ?"

That should keep you busy !

TNS
Title: Re: Question of the Week - Old Version
Post by: tweener on 06/04/2004 22:18:14
Yes.

----
John - The Eternal Pessimist.
Title: Re: Question of the Week - Old Version
Post by: BlooGoo on 08/04/2004 04:57:25
if the car were travelling NEAR the speed of light, and turned on its lights, the way would be lit (i think) because the photons that are emitted from the lights would a) be propelled forward (with some dopplar shifting in there) and b) would be travelling at the speed of light (just that little bit faster than the car itself).

if the car were travelling AT the speed of light ... hmmm ... i would imagine that as the lights were turned on, they would illuminate in front of the car, but as your eyes focused on the light (assuming that you're in the car too) it would look like you're going faster than the light, and would give you the warp speed look that's associated with going really really fast.

just a guess.
Title: Re: Question of the Week - Old Version
Post by: tweener on 08/04/2004 22:51:14
Here's the long version of my previously short answer:

Any photon emitted by your car would travel away from the car at the speed of light, relative to the car.  The photons would also be travelling at the speed of light relative to the signpost at the side of the road.  The photons reflected off the signpost back to your car would arrive at your eye travelling at the speed of light.  There would be considerable doppler shifting here, so that a mere eye would not be able to detect the photons, but with appropriate instrumentation technology, the "way ahead" would be lit.

----
John - The Eternal Pessimist.
Title: Re: Question of the Week - Old Version
Post by: Rabbit on 13/04/2004 18:29:54
Nice Easter question this one! Ask some of the clever boys on the autobahns in Germany, they will have real experience to share with us. No, I do not know any of these people. Come to that, travelling at this speed and messing around with the lights sounds pretty dangerous...
Title: Re: Question of the Week - Old Version
Post by: gsmollin on 15/04/2004 02:40:33
The speed-of-light-car question has a "no" answer, because a car can't travel at the speed of light. We don't ever see the lights come on because time dilation stops the car. All the energy in the universe is required to accelerate the car to the speed of light, and the car gets crushed to infinite density by Lorentz contraction. The light cannot escape the car because it turns into a black hole. This is not a good question.
Title: Re: Question of the Week - Old Version
Post by: MayoFlyFarmer on 15/04/2004 04:44:53
well when you look at it THAT way, maybe its and EXCELLENT question.

If I met you in a scissor-fight, I'd cut off both your wings; on principle alone!!
Title: Re: Question of the Week - Old Version
Post by: neilep on 18/04/2004 17:13:46
Think about the poor copper trying to stop the guy/gal for speeding...by law he will have to travel faster than light to stop the car !!..(I know I know ,it's all silly ! )

'Men are the same as women...just inside out !'
Title: Re: Question of the Week - Old Version
Post by: NakedScientist on 05/04/2004 09:47:30
Here's the answer to the last QOTW "WHY ARE THERE 7 DAYS IN A WEEK, AND WHY DO WE HAVE TO HAVE MONDAYS ?"

It all comes down to the ancient Greeks, Romans and Babylonians.

Early observers of the sky saw several prominent features - the Sun, the Moon, and the stars. But closer inspection of the stars showed that whilst most moved across the sky in a uniform way, some moved at different speeds and even turned back on themselves. These errant stars were named 'wanderers' which in ancient Greek is planetes, from which we get our modern word "planet". At that time early observers only found 5 'planetes' (Mars, Jupiter, Saturn, Mercury and Venus) - the discovery of the rest would have to wait for the telescope to come along.

Observations on these 'planets' showed that they take a different amount of time to complete a cycle and return to their starting position. The planets were assigned a seniority according to how long they took to complete their own cycle :

Saturn 29 years
Jupiter 12 years
Mars 687 days
Sun 365 days
Venus 225 days
Mercury 88 days
Moon 28 days

The Babylonians decided to divide a day into 24 hours (in place of the 12 used by Egyptians) and decided to name each hour of the day after each of the 'planets' in order of seniority, and startign again when you run out of planets. e.g. :

1 am - Saturn
2 am - Jupiter
3 am - Mars
4 am - Sun
5 am - Venus
6 am - Mercury
7 am - Moon ...and start again with...
8 am - Saturn
9 am - Jupiter and so on...
...10 pm Saturn
...11 pm Jupiter
...12 pm Mars

Obviously 7 doesn't divide equally into 24 so the next day starts with a new 'dominant planet' (the one at the top of the list). It was the custom to name the day after the dominant planet on that day.

Looking on the list you can see that after Mars comes "Sun" and hence the next day starts with Sun and works through the list. The day after that starts with "Moon", then "Mars", then "Mercury", then "Jupiter", then Venus and finally back to Saturn.

If you then write out these dominant planets in order you see a familiar pattern emerge :

Planet       English   French

Saturn day   Saturday  Samedi
Sun Day      Sunday    Dimanche
Moon Day     Monday    Lundi
Mars Day     Tuesday   Mardi
Mercury Day  Wednesday Mercredi
Jupiter Day  Thursday  Jeudi
Venus Day    Friday    Vendredi

This 7 day week was adopted by the Romans who spread it across their empire. The Pagan English preferred to keep Sunday for the Sun God, and also named the previous 4 days of the week after Anglo-Saxon gods - Tiw (Tuesday), Woden (Wednesday), Thor (Thursday) and Frig (Friday). The Christians wanted a different holy day to the Jews - so they took Sunday (Dimanche) which is a contraction of Dies Dominici (Day of our Lord) in Latin). Because Sunday is the Christian day of rest, we have to have Monday mornings on which to return to work...ouch.

Title: Re: Question of the Week - Old Version
Post by: NakedScientist on 05/04/2004 09:53:31
Here is this week's QOTW :

"IF A CAR IS DRIVING AT THE SPEED OF LIGHT AND IT TURNS ON ITS HEADLIGHTS, WILL THE WAY AHEAD BE ILLUMINATED ?"

That should keep you busy !

TNS
Title: Re: Question of the Week - Old Version
Post by: tweener on 06/04/2004 22:18:14
Yes.

----
John - The Eternal Pessimist.
Title: Re: Question of the Week - Old Version
Post by: BlooGoo on 08/04/2004 04:57:25
if the car were travelling NEAR the speed of light, and turned on its lights, the way would be lit (i think) because the photons that are emitted from the lights would a) be propelled forward (with some dopplar shifting in there) and b) would be travelling at the speed of light (just that little bit faster than the car itself).

if the car were travelling AT the speed of light ... hmmm ... i would imagine that as the lights were turned on, they would illuminate in front of the car, but as your eyes focused on the light (assuming that you're in the car too) it would look like you're going faster than the light, and would give you the warp speed look that's associated with going really really fast.

just a guess.
Title: Re: Question of the Week - Old Version
Post by: tweener on 08/04/2004 22:51:14
Here's the long version of my previously short answer:

Any photon emitted by your car would travel away from the car at the speed of light, relative to the car.  The photons would also be travelling at the speed of light relative to the signpost at the side of the road.  The photons reflected off the signpost back to your car would arrive at your eye travelling at the speed of light.  There would be considerable doppler shifting here, so that a mere eye would not be able to detect the photons, but with appropriate instrumentation technology, the "way ahead" would be lit.

----
John - The Eternal Pessimist.
Title: Re: Question of the Week - Old Version
Post by: Rabbit on 13/04/2004 18:29:54
Nice Easter question this one! Ask some of the clever boys on the autobahns in Germany, they will have real experience to share with us. No, I do not know any of these people. Come to that, travelling at this speed and messing around with the lights sounds pretty dangerous...
Title: Re: Question of the Week - Old Version
Post by: gsmollin on 15/04/2004 02:40:33
The speed-of-light-car question has a "no" answer, because a car can't travel at the speed of light. We don't ever see the lights come on because time dilation stops the car. All the energy in the universe is required to accelerate the car to the speed of light, and the car gets crushed to infinite density by Lorentz contraction. The light cannot escape the car because it turns into a black hole. This is not a good question.
Title: Re: Question of the Week - Old Version
Post by: MayoFlyFarmer on 15/04/2004 04:44:53
well when you look at it THAT way, maybe its and EXCELLENT question.

If I met you in a scissor-fight, I'd cut off both your wings; on principle alone!!
Title: Re: Question of the Week - Old Version
Post by: neilep on 18/04/2004 17:13:46
Think about the poor copper trying to stop the guy/gal for speeding...by law he will have to travel faster than light to stop the car !!..(I know I know ,it's all silly ! )

'Men are the same as women...just inside out !'
Title: Re: Question of the Week - Old Version
Post by: nilmot on 19/04/2004 08:33:23
I think it has nothing to do with whether the car will be crushed or not. My contribution is (might not be right) that the road in front will not be illuminated because as you are travelling at the speed of light (suppose you can) the light will not have time to hit the road in front and reflect back to your eyes so you can see it. You are travelling as fast as light :)

Tom
Title: Re: Question of the Week - Old Version
Post by: neilep on 19/04/2004 15:43:53
Isn't the speed of light relative to a persons perspective ?(like Tweener has said)...so, from the cars point of view the way ahead will be lit, but from a spectators point of view sitting on a bench as the car goes whizzing by the lights will appear off....(please feel free to castigate and taunt me as my inadequate understanding is made plainly obvious) makes my head-Ache !!! (https://www.thenakedscientists.com/forum/proxy.php?request=http%3A%2F%2Fwww.computerpannen.com%2Fcwm%2Fcwm%2Fcwm%2Fkilltard.gif&hash=0b913ccb288311f9358535f492b78518)

'Men are the same as women...just inside out !'
Title: Re: Question of the Week - Old Version
Post by: gsmollin on 20/04/2004 01:48:08
Special relativity does not tell us what will happen when a car travels at the speed of light, because special relativity prohibits the car from ever attaining the speed of light. Now, one can examine the equations of special relativity, in the limit, as v goes to c, and we can make some extrapolations as to what will be happening as the car gets infinitesimally close to the speed of light.
The light from the headlights still travels at c, as measured by all observers.
The light from the car appears blue-shifted by observers at the stop sign.
The reflected light from the stop sign appears blue-shifted by the car's occupants (assuming the light doesn't just penetrate the stop sign, because it would be of nearly infinite energy), because they see the stop sign approaching them at nearly c.
The usual Lorentz contractions and time dilations occur.

The question posed above asked what happens with a car traveling AT the speed of light. Well, the equations of special relativity return a bunch of singularity points when c is plugged into v, so we don't get any answers.
Title: Re: Question of the Week - Old Version
Post by: neilep on 20/04/2004 03:29:51
Well...seeing as you put it like that !!!...(https://www.thenakedscientists.com/forum/proxy.php?request=http%3A%2F%2Fwww.world-of-smilies.de%2Fhtml%2Fimages%2Fsmilies%2Fkrank%2Fschwitz.gif&hash=04e4901ee66e9ef1c088886beb2bb7f8)..err..no sweat !!! *gulp*

'Men are the same as women...just inside out !'
Title: Re: Question of the Week - Old Version
Post by: Buster on 23/04/2004 18:12:04
Hi all.
I have a question which have bugged me for ages.
If you drilled a hole right through the earth from the north pole to the south pole big enough for a person to fit through and that person jumped into the hole what would happen.Bear in mind gravity comes into play here.This question is in relation to the person and not how the earth would react with a great hole it.
Title: Re: Question of the Week - Old Version
Post by: tweener on 24/04/2004 17:06:25
quote:
Originally posted by Buster

Hi all.
I have a question which have bugged me for ages.
If you drilled a hole right through the earth from the north pole to the south pole big enough for a person to fit through and that person jumped into the hole what would happen.Bear in mind gravity comes into play here.This question is in relation to the person and not how the earth would react with a great hole it.



It was covered recently.  Here is the link:

http://www.thenakedscientists.com/forum/topic.asp?TOPIC_ID=850&SearchTerms=gravity,earth

----
John - The Eternal Pessimist.
Title: Re: Question of the Week - Old Version
Post by: Dan B on 04/05/2004 01:09:21
The way ahead would be lit, RELATIVE to the car [:D] A better question would be "how come we can see the beam of energy that comes from a star trek phaser?"
Title: Re: Question of the Week - Old Version
Post by: Dan B on 04/05/2004 01:12:46
quote:
Originally posted by Buster

Hi all.
I have a question which have bugged me for ages.
If you drilled a hole right through the earth from the north pole to the south pole big enough for a person to fit through and that person jumped into the hole what would happen.Bear in mind gravity comes into play here.This question is in relation to the person and not how the earth would react with a great hole it.



The question wasn't exactly answered by the link above. You would fall towards the centre, pass it, be drawn back, then "oscillate" about it [:D]
Title: Re: Question of the Week - Old Version
Post by: neilep on 04/05/2004 01:43:30
quote:
Originally posted by Dan B

The way ahead would be lit, RELATIVE to the car [:D] A better question would be "how come we can see the beam of energy that comes from a star trek phaser?"



You cant see it !!..its there specifically for special effect.

'Men are the same as women...just inside out !'(https://www.thenakedscientists.com/forum/proxy.php?request=http%3A%2F%2Fwww.world-of-smilies.de%2Fhtml%2Fimages%2Fsmilies%2Flove%2F2015.gif&hash=901cd12278f46c3480e43bc40519e7fb)
Title: Re: Question of the Week - Old Version
Post by: Dan B on 04/05/2004 14:38:32
[xx(] spoil sport [:D]
Title: Re: Question of the Week - Old Version
Post by: neilep on 04/05/2004 14:40:16
Soz Dan B....forgive ?

'Men are the same as women...just inside out !'(https://www.thenakedscientists.com/forum/proxy.php?request=http%3A%2F%2Fwww.world-of-smilies.de%2Fhtml%2Fimages%2Fsmilies%2Flove%2F2015.gif&hash=901cd12278f46c3480e43bc40519e7fb)
Title: Re: Question of the Week - Old Version
Post by: Dan B on 04/05/2004 20:39:25
[:D] maybe.
Title: Re: Question of the Week - Old Version
Post by: NakedScientist on 14/05/2004 04:36:53
Sorry for the delay in the appearance of the latest QOTW, but here it is :

"WHEN YOU WALK AROUND AT HOME BAREFOOT, WHY DO SOME SURFACES FEEL WARM, YET OTHERS FEEL COLD, EVEN THOUGH BOTH SURFACES ARE ACTUALLY AT THE SAME TEMPERATURE ?"

TNS
Title: Re: Question of the Week - Old Version
Post by: cuso4 on 14/05/2004 08:11:21
It's all to do with the thermal conductivity of materials. For example if you stand on a piece of metal bare foot(let's say that the temperature of the foot is higher than that of the metal) you feel cold because heat is transferred to the metal. However, if you stand on a piece of wood it doesn't feel as cold because wood is a poor thermal conductor and the heat from your foot doesn't transfer to the wood as efficently.

Angel
Title: Re: Question of the Week - Old Version
Post by: neilep on 14/05/2004 12:39:49
Well, as an experiment for 'The Naked Scientists' I just instructed my family...(well..not wifey...she's on the phone BLAH BLAH BLAH')...erhhmm...as I was saying me and the kids just went barefeet and walked ariound the house !!...we discovered that the kitchen tiles were cold, the lounge carpets were warm, and the parquet flooring in the bathroom was warm.....then we all walked over burning hot coals and they were hot !!....then we stuck our feet in the freezer and that was cold.....hope my experiment helps.



'Men are the same as women...just inside out !'  (https://www.thenakedscientists.com/forum/proxy.php?request=http%3A%2F%2Finstagiber.net%2Fsmiliesdotcom%2Fcwm%2Fcwm%2Frcain.gif&hash=32ae7f4f03d740b017b01cda28addd79)
Title: Re: Question of the Week - Old Version
Post by: NakedScientist on 31/05/2004 02:01:34
Angel was absolutely right with her explanation of why some surfaces  feel warm to the touch, whilst other surfaces, despite being at the same temperature, feel cold.

Now here's this week's QOTW

HOW DOES SUNSCREEN PROTECT YOU FROM THE SUN ?

TNS
Title: Re: Question of the Week - Old Version
Post by: Rokitansky on 31/05/2004 15:14:04
It filters sunrays in a specific part of a spectrum, part of which is hazard to humans  ?
Title: Re: Question of the Week - Old Version
Post by: Trang on 06/06/2004 04:24:04
HOW DOES SUNSCREEN PROTECT YOU FROM THE SUN
just becuse of the layer (O3.)
But more details...
sorry [:I]

Chemistry is my love
Title: Re: Question of the Week - Old Version
Post by: chris on 11/06/2004 06:49:43
No one seems to have been particularly keen on tackling this one...so I will :(

Sunburn occurs when the skin is damaged by ultraviolet (UV) radiation in sunlight. This is short-wavelength radiation lying just outside the visible spectrum and is mostly mopped up by the ozone layer (O3) in the upper atmosphere. UV radiation is dangerous because it can damage DNA in skin cells, potentially triggering skin cancer. The skin responds to UV exposure by increasing the production of the dark pigment melanin, which is secreted into the skin by a population of cells called melanocytes. Melanin absorbs UV very efficiently, preventing further UV radiation from reaching the nucleated (DNA-containing) cells deeper in the skin, and hence preventing DNA damage.

Sunscreen essentially does the same job as melanin. It contains molecules which absorb ultraviolet radiation and change it into less harmful forms of energy, mainly heat (infrared). Having said that, reports have claimed that some sunscreens might not be as safe as others. Indeed some may be re-emitting radiation that is almost as harmful as UV...

We discussed this issue on the radio in January - here's the link :

http://www.thenakedscientists.com/html/shows/2004.01.25.htm

Chris

"I never forget a face, but in your case I'll make an exception"
 - Groucho Marx
Title: Re: Question of the Week - Old Version
Post by: NakedScientist on 13/06/2004 07:46:39
Here is this week's QOTW

WHAT IS LIGHTNING, WHY DOES IT OCCUR, AND HOW IS IT PRODUCED ?

TNS
Title: Re: Question of the Week - Old Version
Post by: Donnah on 14/06/2004 21:32:35
It's light caused by the discharge of electricity between two electrified cloud masses or a cloud and the earth.  I have no idea how it's produced, but now I'm curious.
Title: Re: Question of the Week - Old Version
Post by: nilmot on 17/06/2004 10:50:35
Is it the charge is so strong that it ionise the surrounding air? I think it's something along those lines.

Tom
Title: Re: Question of the Week - Old Version
Post by: OmnipotentOne on 21/06/2004 21:45:27
Visible discharge of electricity when part of the atmosphere acquires enough electrical charge to overcome the resistance of the air.


To see the world through a grain of sand.
Title: Re: Question of the Week - Old Version
Post by: tweener on 22/06/2004 21:20:40
Lightning is the discharge of electric charge between clouds or a cloud and the ground.  It is not clearly understood what causes the migration of the charge in the first place.  Positive charge collects at the top of the cloud, while negative charge build up at the bottom.  When the charge builds to a high enough level, possibly many millions of volts, an ionized channel is formed and a current flows to equalize the charge.

----
John - The Eternal Pessimist.
Title: Re: Question of the Week - Old Version
Post by: neilep on 22/06/2004 21:34:26
So clouds become big balls of fluffy batteries then eh ?[:D]

'Men are the same as women...just inside out !' (https://www.thenakedscientists.com/forum/proxy.php?request=http%3A%2F%2Fwww.world-of-smilies.de%2Fhtml%2Fimages%2Fsmilies%2FSchilder2%2Finsanes.gif&hash=4f18432872d0188852a6f4a3170ec758)
Title: Re: Question of the Week - Old Version
Post by: tweener on 23/06/2004 04:01:25
Yeah!  If you could figure out how to capture and store the energy, you could power a fair sized city for several days on the power generated in a single thunderstorm.  And you might just become relatively wealthy too!

----
John - The Eternal Pessimist.
Title: Re: Question of the Week - Old Version
Post by: neilep on 23/06/2004 14:19:39
I've got myself a very tall ladder, some empty batteries and some rubber gloves.....hang on !!..if i get all the clouds interested in playing musical instruments then perhaps I can be a Lightning Conductor !!!! *oh god...someone ban me from this site please *

'Men are the same as women...just inside out !' (https://www.thenakedscientists.com/forum/proxy.php?request=http%3A%2F%2Fwww.world-of-smilies.de%2Fhtml%2Fimages%2Fsmilies%2FSchilder2%2Finsanes.gif&hash=4f18432872d0188852a6f4a3170ec758)
Title: Re: Question of the Week - Old Version
Post by: NakedScientist on 08/07/2004 08:41:37
ANSWER TO "WHAT IS LIGHTNING, WHY DOES IT OCCUR, AND HOW IS IT PRODUCED ?"

At any given instant there are 2,000 thunderstorms happening around the world, producing a 100 lightning strikes a second, or 8 million lightning strikes a day !

Lightning is an electrical discharge between one cloud and another, or between a cloud and the Earth, accompanied by the emission of light.

This electricity originates in clouds which behave like giant capacitors or accumulators in the sky. Collisions between the water particles (called hydrometeors) which make up the clouds lead to the smaller particles acquiring a positive charge and the larger particles acquiring a negative charge. The precise mechanism by which this happens is not fully understood.

Under the influence of updrafts, the small particles (carrying a net positive charge) are carried to the top of the cloud, leaving a net negative charge concentrated at the bottom of the cloud. This can lead to the accumulation of a large potential difference exceeding millions of volts.

This electrical potential creates a strong electric field between the clouds and the ground (earth) which is sufficient to cause the earth's surface to become positively charged as electrons are repelled away.

When the field becomes sufficiently strong to overcome the resistance of the air, the cloud discharges to earth, producing a lightning bolt.

Each lightning flash is about 3 miles long but only about a centimetre wide. It discharges about 1-10 billion joules of energy, produces a current of some 20,000 amps, heats the surrounding air to a temperature 3 - 5 times hotter (20,000 degrees C) than the surface of the sun (6000 degrees C), and is actually made up of 3 or so 'strokes' lasting only a matter of milliseconds or less.

So with all that energy, could lightning be collected to power a town ?

No - simple maths shows that this is not feasible :

100 joules of energy keeps a 100 watt lightbulb burning for 1 second. So 1 billion joules of energy (the amount in a modest lightning strike) would keep the same single lightbulb burning for just under 120 days.

The average household uses about 500-1000 kilowatt hours (kWh) per month. 1 kilowatt hour is 1000 Joules per second x 3600 seconds (the number of seconds in an hour); i.e. 3,600000 Joules. So the average household consumes about 500 x 3,600000 = 1.8 billion joules per month.

So if you could collect all of the energy contained in one lightning strike it would run one home for a month.

Sounds like good news, but not all of the energy in lightning is available as electricity - in fact probably less than 1% of the energy (10 million joules or so) could be effectively harnessed as electricity.

Then you have to take into consideration the 'strike frequency' for any given area, the cost involved in building a tall tower to work as a lightning collector, and then tackle the problem of how to construct a sufficiently big capacitor to store all of the charge you collect...

And what about thunder ?

The intense heat of the lightning disharge (over 20,000 degrees C) superheats the surrounding air causing it to expand explosively. This creates a compression or 'shock' wave - the thunder - which spreads out through the air in all directions, travelling at about a fifth of a mile per second.

The flash and the thunder clap are produced simultaneously - as anyone unlucky enough to have ever got very close to a lightning strike can tell you - but the light from the flash travels much more rapidly (186,000 miles per second) than sound (0.2 miles per second approximately). The light therefore reaches you first, then a short while later (depending upon how far away the storm is), the thunder rolls in.

TNS
Title: Re: Question of the Week - Old Version
Post by: NakedScientist on 08/07/2004 08:45:31
Here's this week's QOTW :

"WHAT MAKES THE HANDS GLOW ON A CLOCK OR WATCH FACE ?"

TNS
Title: Re: Question of the Week - Old Version
Post by: jai on 08/07/2004 23:38:57
ahhh! isnt it that glow in the dark paint that they put on it?

or alternatively, for those clocks that do not contain such advanced technology, is it that the hands are just above the surface of the clock face? so that in low light, even when there are no visible shadows there is an almost impercepatable diffence in the shade of colour caused by the shadow of the hands. this difference in shade, though not always noticed  tricks the eye into thinking that the hands are lighter in shade - or glowing. much in the same way that some of those cool sixties paintings make your eyes wobble and the colours jump out and move (though that has to do with the colour perception and the tone value or something like that).
Title: Re: Question of the Week - Old Version
Post by: jai on 12/07/2004 23:49:29
also just fournd out, courtesy of my dad, that the old clock and watch hands used to contain radium to make them glow. the new glow in the dark hands are just a flourescing paint rather than a paint with a half life of it's own....

yes, but.........
Title: Re: Question of the Week - Old Version
Post by: Furwa on 13/07/2004 01:31:37
Its flourescent paint/sticker =D
And so um it glows...Like all other flourscent stuff.
Title: Re: Question of the Week - Old Version
Post by: gsmollin on 22/07/2004 17:29:38
There are several right answers to this one.
1) Years ago the answer was radium-laced paint. I had one of those watches, and I could see the scintillation discharges in the clock face, in the dark, if I used an eye loupe. Legend has it that the unfortunate women who painted the watch faces by hand used to point their brushes by twirling them in their mouths. If this is true, the radium would have caused their jaws to fall off.
2) Today, watches use a phos-phorescent paint that stores light energy, then releases it in the dark. These are not nearly as bright as the radium dials were.
3) There was an expensive watch, advertised some years ago, that claimed to be filled with tritium, which made its dial glow brightly in the dark.
4) Lately, electro-flourescent screens have become common on electronic digital watches. Although I haven't personally seen these used on a watch with hands, it is probably possible to engineer one.
Title: Re: Question of the Week - Old Version
Post by: gsmollin on 22/07/2004 17:35:39
As an aside to last week's lightning question (great essay, NS), I was unfortunate to be within a few feet of a lightning discharge once, and my salient memory is the nature of the sound it produced. We are used to rumbles, booms, and bangs from thunder. When one is close enough, the sound is the most intense SNAP one has ever heard. The electrical nature is un-mistakable.
Title: Re: Question of the Week - Old Version
Post by: NakedScientist on 23/08/2004 12:35:24
ANSWER TO "HOW DOES GLOW IN THE DARK PLASTIC WORK AND WHAT MAKES THE HANDS ON WATCHES GLOW"

The answers given above are pretty much correct.

Things that glow in the dark are referred to as 'phosphors' and are materials which can soak up energy and then re-radiate it as visible light. Put simply, when these substances absorb energy (in the form of light, heat or radiation) some of their electrons become excited and are catapulted up to a higher energy state. Light is emitted (and the substance glows) when the excited electrons fall back to their 'ground state', releasing the extra energy that they picked up previously.

Television screens (the non-LCD / Plasma screen variety) and fluorescent tubes (strip lights) rely on precisely this effect. In a TV the screen is coated with a phosphor which is excited by a stream of electrons produced by a cathode ray gun at the back of the set. In a strip light the electricity excites electrons in the atoms of the metallic element mercury. The excited mercury atoms emit ultraviolet light which hits the phosphor coating on the glass of the tube, which in turn then emits visible (white) light.

The phosphors used in glow in the dark stickers and badges, clock and watch faces commonly contain the compounds zinc sulphide (often with some copper mixed in too) or strontium aluminate. These substances are added to the polymer used to make the plastic. They produce a soft green glow which can, with the correct engineering, persist for minutes to hours.

Another way to make things glow in the dark, but without them needing to be 'charged up' by prior exposure to light, is to use a long-lived radioactive substance, such as radium. The radioactive material can be combined with an appropriate phosphor which is excited by the radioactivity and converts the energy of the radiation into visible light - making the hands of the clock or watch glow.

So, in summary, cheaper clocks and watches use phosphors which soak up light and then release it very slowly to make their hands glow for several hours afterwards. More expensive (and military) timepieces rely on a radioactive substance to energise the phosphor so that they can glow continuously.
Title: Re: Question of the Week - Old Version
Post by: roberth on 23/08/2004 23:57:06
So, TNS, are you saying that my watch (Rolex Submariner) contains a radioactive substance? I thought that they stopped using that stuff a while ago.
Title: Re: Question of the Week - Old Version
Post by: NakedScientist on 24/08/2004 09:37:50
The substance used (as correctly stated above) is a paint containing tritium (an isotope of hydrogen which decays (breaks down) emitting beta particles (fast moving electrons)). These beta particles excite a phosphor (also in the paint) which converts the energy from the beta particle into visible light.

The half life of tritium is 12.3 years. In other words, every 12.3 years the number of radioactive nuclei has declined by half. So you might need to get the paint touched up to keep the glow as bright.

I think Rolex, certainly in the past, use(d) precisely this technique to keep their watches glowing.

TNS
Title: Re: Question of the Week - Old Version
Post by: NakedScientist on 24/08/2004 11:47:07
Here's this week's QOTW :

WHAT IS A SHOOTING STAR ? IS IT REALLY A STAR ?
Title: Re: Question of the Week - Old Version
Post by: roberth on 25/08/2004 00:00:01
I think a shooting star is a small asteroid or space rock burning up as it enters the Earth's atmosphere. It's not a star.
Title: Re: Question of the Week - Old Version
Post by: OmnipotentOne on 25/08/2004 16:17:29
yeah he's pretty much got it, a meteor that hits the earths atmosphere and burns up on the way in, causing that streak of light.

To see a world in a grain of sand.
Title: Re: Question of the Week - Old Version
Post by: gsmollin on 26/08/2004 05:24:13
Yea, come on, NS, you can do better than that. Why don't you ask what shooting stars are composed of?
Title: Re: Question of the Week - Old Version
Post by: NakedScientist on 27/08/2004 09:38:29
Better still, why don't you tell us ! [;)]
Title: Re: Question of the Week - Old Version
Post by: NakedScientist on 03/09/2004 10:49:24
HERE IS THIS WEEK'S QOTW :

WHAT IS THE 'FOG' THAT APPEARS FROM THE TOP OF A BOTTLE OF FIZZY DRINK OR CHAMPAGNE AFTER YOU OPEN IT ?

(Hint - we're not talking about the drink spraying up when you shake the bottle !)

TNS
Title: Re: Question of the Week - Old Version
Post by: gsmollin on 03/09/2004 17:04:15
Meteorites: There are two basic kinds, stoney and iron. Stoney meteororites have been hard to find, since they look like any other stone, but they have been collected from Antarctic glaciers in substantial numbers. The other type is the iron meteorite, containing up to 15% nickel. These are the more famous type, and some large ones have been found. Their crystal structure is consistent with having been cooled at a depth of a hundred kilometers or so inside of an asteroid, then having been released by a collision.

Pop-bottle fog: The fog is composed of very small dilute carbonic acid droplets. The fog is produced by the sudden pressure drop inside the bottle when you open it. A bottle of "fizzy drink or champagne" is carbonated- it contains carbon dioxide gas dissolved in water, aka carbonic acid. The high pressure inside the bottle maintains the vapor pressure of the carbonic acid in equilibrium. When you open it, the carbon dioxide comes out of solution and forms the bubbles we see in fizzy drinks. At the same time, the pressure in the gas over the liquid in the bottle decreases, and the gas becomes supersaturated with the water vapor and CO2, and forms a fog.
Title: Re: Question of the Week - Old Version
Post by: NakedScientist on 15/09/2004 08:41:01
An interesting addendum about meteorites :

Scientists at the University of Arizona announced recently that they think life may have started with help from a meteorite. Their argument centres on the element phosphorus (P), which plays a pivotal role in life's biology. It forms the backbone of our genetic material (DNA and RNA), stabilises our cell membranes (as phospholipids) and provides cells with the molecular equivalent of a rechargeable battery (as the ubiquitous energy molecule ATP).

But in the early earth 4000 million years ago, when life began, phosphorus was relatively scarce because it was locked up in stable, unreactive, minerals like apatite (calcium phosphate).

So it seems strange that such a rare chemical (in terms of its chemical availability) should be given such a central role in developing life. Unless, of course, life began in a place richly endowed with chemically reactive phosphorus...around a meteorite impact site, for instance.

Meteorites fall into 2 broad categories (as gsmollin has clearly explained above) - petrous (stony) and ferrous (irony!). Iron meteorites contain iron and another mineral, schreibersite, which is iron nickel phosphide and very rare on earth.

But unlike Earth's unreactive forms of phosphorus (apatite), schreibersite eagerly participates in reactions with fresh water to produce phosphorus compounds very similar to those found in life today, elading scientists to speculate that a meteorite impact might have provided the catalyst that got life started on the early earth.

The Arizona scientists argue that if an iron-rich meteorite (containing schreibersite) crash landed in a pool of fresh water the  area would become enriched with biologically useful forms of phosphorus, perhaps explaining how "The Devils Element" landed the lead role in the story of life.
Title: Re: Question of the Week - Old Version
Post by: neilep on 15/09/2004 08:55:47
...and I always thought Meteorites was a religious or other solemn ceremony conducted seconds before spacey rocky slammed into the planet ...oh well...guess I got that wrong.

'Men are the same as women...just inside out !' (https://www.thenakedscientists.com/forum/proxy.php?request=http%3A%2F%2Fwww.world-of-smilies.de%2Fhtml%2Fimages%2Fsmilies%2FSchilder2%2Finsanes.gif&hash=4f18432872d0188852a6f4a3170ec758)
Title: Re: Question of the Week - Old Version
Post by: NakedScientist on 15/09/2004 09:01:51
ANSWER TO LAST WEEK'S QOTW "WHAT IS THE 'FOG' THAT APPEARS FROM THE TOP OF A BOTTLE OF FIZZY DRINK OR CHAMPAGNE AFTER YOU OPEN IT ?"

Fizzy drinks are saturated with carbon dioxide. When you open the bottle the escaping gas bubbles carry tiny droplets of water into the neck of the bottle. At the same time, the pressure above the liquid (keeping the carbon dioxide in solution) suddenly drops, which causes the temperature to fall.

The principle is the same as a fridge which cools the interior by rapidly expanding a compressed gas. The huge increase in entropy associated with the expansion of the gas more than accommodates a small enthalpy (temperature) decrease.

In the bottle neck the lowered temperature allows the water droplets carried out by the escaping gas to cling together by a process called hydrogen bonding. Water molecules resemble tiny boomerangs with an oxygen atom at the centre and a hydrogen atom forming each 'arm'. Because the oxygen attracts electrons more strongly than hydrogen the oxygen is slightly negatively charged and the hydrogens are slightly positive. These charge differences can weakly glue different water molecules together so they hang in a fog. Because the effect is very weak, the fog rapidly disappears when the temperature rises and the molecules start to move about too quickly to hang together.

So there you have it, the origin of fizz bottle fog.

TNS
Title: Re: Question of the Week - Old Version
Post by: NakedScientist on 16/09/2004 15:45:09
HERE IS THIS WEEK'S QOTW :

"HOW DO MATCHES WORK ? WHAT MAKES A SAFETY MATCH 'SAFE' ?"

TNS
Title: Re: Question of the Week - Old Version
Post by: nilmot on 17/09/2004 13:20:55
Matches have sulphur and other chemical which I don't know yet but I will find out because i saw it on a book before, when scrapped against a rough surface that provides the energy needed for the reaction.

When matches were invented it was originally found by a scientist John Walker where he was stiring potassium cabonate and antimony with a stick. He scraped the stck on the floor with purpose of getting rid of the chemical but the mixture caugth fire.

They use to self combust because the mixture of chemical was reactive enough when it have contact with air and light. 'Something' which I will also find out were added to it to prevent it from happening.

Tom
Title: Re: Question of the Week - Old Version
Post by: nilmot on 20/09/2004 13:09:34
Sorry, just found out that it's not sulphur, it's phosphurous

Tom
Title: Re: Question of the Week - Old Version
Post by: nilmot on 23/09/2004 08:38:25
And the safe thing that makes it safe is potassium chlorate on the head of the match and phosphorous based chemical on the striking surface. They don't mix until match is stuck.

Tom
Title: Re: Question of the Week - Old Version
Post by: NakedScientist on 15/11/2004 09:43:58
QOTW needs resurrecting and that's partly my fault for taking ages to post the answer to this question and then publish the next one.

ANSWER TO "WHAT IS A SAFETY MATCH"

Matches were invented by the English apothecary John Walker in 1826-7 when he made a mixture of antimony sulphide and potassium chlorate for a client. He accidentally dropped some of the mixture which, upon impact, promptly ignited. Adding a stick and refining the recipe he produced the world's first friction matches, containing antimony sulfide, potassium chlorate, gum, and starch.

Walker was not an astute businessman and made no money from his invention. Indeed, it was another individual - Samuel Jones - who was already into matchmaking - who realised the huge commercial potential of a readily available source of fire and patented the invention under his own name. His brand of matches, based on the same recipe, were called Lucifers and were a runaway success.

But the problem with Walker and Jones's matches was that they were not terribly safe - they ignited in an explosive manner, produced a terrible smell when lit, and were poisonous ! They were, however, a runaway success and sales rocketed (pardon the pun).

Then, in 1832, Richard Bell established the first British match factory in London. He began producing a new phosphorus-containing match that had been invented by Frenchman Charles Sauria. The match head contained a mixture of sulphur, potassium chlorate, antimony sulphide, and white phosphorus. The addition of phosphorus made striking the match much easier to accomplish, but had the downside of poisoning people. The workers in the match factory developed phossy-jaw (an erosive disease of the lower jaw caused by long term exposure to white phosphorus), and children developed other bony abnormalities. A match box also contained enough white phosphorous to kill someone, and the matches kept setting fire to things they shouldn't - largely because all the chemicals needed for ignition were jammed together into the match head and all that was needed to kick-start the reaction was  some energy.

This problem was solved in 1844 when the Swedish chemist Gustav Pasch began separating the chemicals in a match head, placing some on the side of the matchbox, and the rest on the match head. The match could then only be struck against the side of the box - and that's the safety match. Another safety measure, which came later, was the subsitution of the less reactive red phosphorus for its more violent white counterpart.

The present day recipe for a match comprises a wooden or cardboard splint impregnated with ammonium phosphate (to stop it smouldering after being blown out), coated on the end with a mixture of gum, potassium chlorate, glass powder (to create the friction on striking), and sulphur.

The sulphur is the fuel which consumes the oxygen released by the potassium chlorate. The red phosphorus on the matchbox kickstarts the reaction rather than being used as a fuel (as in the early match recipes).

So there you have it, the history of matchmaking, and why a safety match is a safety match !
Title: Re: Question of the Week - Old Version
Post by: NakedScientist on 15/11/2004 09:49:32
HERE'S THE NEW QOTW :

WHY DO PLANETS SPIN, INCLUDING ORBITING THE SUN ?
Title: Re: Question of the Week - Old Version
Post by: gsmollin on 17/11/2004 02:30:59
NS, you should change the name to "Question of the Quarter", since the last question you posed was in September!

Anyway, planets spin and orbit the sun because the angular momentum posessed by the original gas and dust that collapsed to form the solar system is still conserved today.

In more detail, large clouds of gas and dust exist throughout the universe. They do not all collapse, because the clouds contain kinetic and thermal energy that resists gravitational collapse. However, if a volume of the cloud reaches a critical density, it will begin gravitational collapse. Frequently, the seed for the collapse is caused by a supernova explosion that compresses the cloud. Gravitational tidal forces from colliding galaxies can also begin collapse of gas clouds.

However it starts, the cloud must rid itself of its kinetic energy, and its gravitational binding energy, in order to collapse. It is mostly radiated away as thermal energy, but the cloud will eventually become opaque and convection will become important. Some protostars also radiate the energy as jets.

Another problem is the magnetic field of the collapsing cloud. As the size of the cloud shrinks, the strength of the magnetic field will grow, and may prevent further collapse. Ridding the cloud of the magnetic field is one of the many mysteries of stellar formation. It is possible that magnetic fields and rotational energy are eliminated together by the bipolar jets seen in nebula where protostars are presumably found. It is likely that the magnetic field energy has an important effect on the ultimate size and shape of the final solar system, just as the angular momentum, temperature, and kinetic energy of the collapsing cloud.

The angular mometum possessed by the original cloud is conserved: It cannot be radiated like the energy can. As the size of the cloud shrinks under gravitational collapse, the rotational rates begin to speed up. The cloud may break up into two to more clouds depending upon the amount and distribution of its angular momentum. The cloud forms a flat disc along a common rotational axis. If a star is to form at the center, it must rid itself of most of its angular momentum. This is accomplished by the protostar shedding mass through a solar wind. Much of that material remains in the disc, and adds to the coalesceing material in the disc. If the angular momentum is large enough, a binary star system may form. If there is less angular momentum, then planets form around the star. The planets all orbit in the same direction as the original cloud rotated, in a disc. They also spin in the same direction, at least in the beginning. As planetary formation continues, large planetoids may strike a planet and tip its axis of rotation. There can also be gravitational resonances, and tidal effects in planets near the central star, or stars, that will affect rotational rates and axis directions.

A related question is "Why do the planets all orbit at low inclinations to the ecliptic, i.e. why aren't there planets orbiting over the north and south poles of the sun?"
Title: Re: Question of the Week - Old Version
Post by: NakedScientist on 23/11/2004 10:26:08
There's not much I can add to gsmollin's excellent synopsis regarding planetary spin.

So here's this week's QOTW :

IF THE RETINA NEEDS LIGHT TO 'SEE', HOW DOES IT SEE THINGS THAT ARE 'BLACK' ?

Fire away...

TNS
Title: Re: Question of the Week - Old Version
Post by: neilep on 23/11/2004 11:27:18
Last time I looked I discovered that I'm not an Optician or eye doctor, but would the lack of light in itself be a way for the brain to construct the object that is not reflecting the light ?, if light is being received from everything but the object which is black then the the 'gap' itself is the construct ....even items which are black do reflect something, enough for the brain to construct outlines, edges, impressions, contours etc etc

'Men are the same as women...just inside out !'
Title: Re: Question of the Week - Old Version
Post by: DrN on 23/11/2004 20:42:10
I agree with Neil. Black absorbs light, rather than reflecting it, so it must be an absence of light. hence 'darkness' at night being perceived by our eyes as black.
Title: Re: Question of the Week - Old Version
Post by: NakedScientist on 29/11/2004 10:46:33
ANSWER TO LAST WEEK'S QOTW :

"IF THE RETINA NEEDS LIGHT TO 'SEE', HOW DOES IT SEE THINGS THAT ARE 'BLACK' ?"

The answer to this question lies within the retina itself. The retina consists of a sheet of cells, several layers thick, at the back of the eye. The top layer contains the photoreceptors or 'rods and cones', which contain light-sensitive pigment called rhodopsin comprising a protein - opsin - fused to retinal (the light sensitive part of the molecle) which is derived from vitamin A.

There are about 110 million rods in each eye (which see in black and white) and about 6.5 million cones (which see in colour - 62% are red cones, 32% are green, and 2% are blue). These photoreceptors connect to 'bipolar cells' which then link up with retinal ganglion cells. The retinal ganglion cells are responsible for transmitting the image to the brain. Here's a retinal schematic :

(https://www.thenakedscientists.com/forum/proxy.php?request=http%3A%2F%2Fwww.siggraph.org%2Feducation%2Fmaterials%2FHyperVis%2Fvision%2Fretina.gif&hash=455691b1a6ca617522202da24f712837)

Intuitively one would think that when light shines on a photoreceptor it activates it, but in fact the opposite is true.  Light shining on a photoreceptor actually switches it OFF. When a photon of light hits a rod or cone it causes the rhodopsin to dissociate into its retinal and opsin components. This leads to the production of a chemical messenger which turns off the flow of sodium ions into the cell, hyperpolarising it, and hence making it less active.

The increased activity seen in the absence of light is referred to as the 'dark current' and, paradoxically, the retina is far more active in the dark than it is in the light.

So you do actually actively 'see' black, because the lack of light hitting photoreceptors makes them much more active.

Here's an overview of retinal physiology :
http://sky.bsd.uchicago.edu/lcy_ref/synap/retina.html

TNS
Title: Re: Question of the Week - Old Version
Post by: NakedScientist on 29/11/2004 10:51:26
HERE'S THIS WEEK'S QOTW

"HOW DOES WINDSCREEN DE-ICER SPRAY WORK ?"

TNS
Title: Re: Question of the Week - Old Version
Post by: DrPhil on 29/11/2004 12:01:21
I have tried several different brands and found that they don't work very well. :)
Title: Re: Question of the Week - Old Version
Post by: chris on 29/11/2004 13:13:32
It worked okay for me the other day !

Sorry to hear your's works less well, but how does it work in theory ?

Chris

"I never forget a face, but in your case I'll make an exception"
 - Groucho Marx
Title: Re: Question of the Week - Old Version
Post by: chris on 29/11/2004 13:17:02
It worked okay for me the other day !

Sorry to hear your's works less well, but how does it work in theory ?

Chris

"I never forget a face, but in your case I'll make an exception"
 - Groucho Marx
Title: Re: Question of the Week - Old Version
Post by: DrPhil on 29/11/2004 15:22:13
Works well in theory but not in practice.
Title: Re: Question of the Week - Old Version
Post by: DrN on 29/11/2004 21:38:12
is it like adding salt to water reduces the temperature at which it freezes, by interfering with the hydrogen bonding? so de-icer would presumably do the same. I remember that the salt experiment reduced the freezing point by 10 C (probably added to saturation), so based on this theory, whether it worked or not would depend on how cold it was! using salt, it would mean the temp would have to be below -10 C before it didn't work. presumably the solvents in de-icer take the temp threshold further.
Title: Re: Question of the Week - Old Version
Post by: DrPhil on 30/11/2004 15:29:16
My guess??... Depression of the freezing point is due to a lowering of the concentration of water molecules. As the deicing chemical dissolves in a little water, the particles are randomly distributed amongst the water molecules.  The particles simply get in the way of the water molecules when they attempt to form the highly ordered pattern of the solid phase.  Hence a lower temperature is required to get the solution to freeze.
Title: Re: Question of the Week - Old Version
Post by: DrN on 01/12/2004 09:33:00
yes, thats a more coherent way of putting it! I looked at my can of de-icer and its essentially propan-2-ol, and it works up to -15 C. the only thing is - how does the propanol dilute frozen, solid, water? it must break the bonds somehow. chemistry was never my strong point.
Title: Re: Question of the Week - Old Version
Post by: DrPhil on 01/12/2004 11:08:09
I know that salts have an exothermic heat of solution (or is it heat of hydration; I'm not a chemist either) that assists in melting the ice. But that doesn't explain how the non salt-based products work.

I also know that aircraft deicers are usually applied hot. The hot liquid melts the ice and then the freezing point depression properties of the solution prevent re-freezing. But that doesn't explain how the deicers that we may use on our cars might work. If you're like me you store the stuff in the trunk of your car and it probably starts out at the same temperature as the ice it's trying to melt.

Then there are the glycols which have a couple of ď-OHĒ (hydroxyl) groups that can break up the hydrogen bond in water. I suppose that this could break apart the ice crystals.
Title: Re: Question of the Week - Old Version
Post by: NakedScientist on 07/12/2004 11:27:19
ANSWER TO LAST WEEK'S QOTW :

"HOW DOES WINDSCREEN DE-ICER SPRAY WORK ?"

You're almost there. De-icer is indeed iso-propanol, an alcohol not greatly dissimilar to the alcohol in a bottle of gin or whisky.

Alcohols dissolve because they have a hydroxyl (OH) group attached to the molecule. This chemical group is very polar (pardon the pun in the context of de-icer). The oxygen atom loves electrons and pulls them towards itself very strongly, including the electron from the hydrogen that is bonded to it.

This makes the hydrogen a little bit positive, and the oxygen a little bit negative and enables it to take part in a process called hydrogen bonding. This is what makes water 'sticky' and why you can bend a stream of water with the static electricity on a comb, because all of the molecules cling together by the positive hydrogens attracting the negative oxygens on adjacent molecules.

So the alcohol can dissolve in water because it can take part in the same hydrogen bonding process. But because the alcohol molecule is much bigger than a water molecule, and a funny shape, it prevents the water molecules lining up so easily to get close enough together to form a solid crystal i.e. freeze. To do that you need to make the conditions much much colder. This is how antifreeze works. A big ethylene glycol molecule links up with lots of water molecules (and dissolves quite happily), but because it is a funny shape it prevents big regular ice crystals from forming, so even if you car radiator does begin to freeze the best it can do is form slush which won't burst your pipes.

So how does the de-icer melt the ice to start with? Well, the alcohol in the tin is concentrated. When you add it to the ice on the window, the diluting effect of the ice and concentrated alcohol mixing produces a little bit of heat which speeds up the melting process. Then the alcohol and water mix thoroughly, the alcohol dissoves in the water, lowering its melting point and preventing re-freezing.

Occasionally you can make the ice re-freeze but this is usually on an exceptionally cold day with a particularly thick layer of ice, so the concentration of alcohol in the water remains too low.

So that's how de-icer works (in theory !)

TNS
Title: Re: Question of the Week - Old Version
Post by: NakedScientist on 07/12/2004 11:30:13
Here's this week's QOTW

"WHAT MAKES YOUR JOINTS 'CRACK' FROM TIME TO TIME ?"

TNS
Title: Re: Question of the Week - Old Version
Post by: neilep on 07/12/2004 19:52:34
quote:
Originally posted by NakedScientist

Here's this week's QOTW

"WHAT MAKES YOUR JOINTS 'CRACK' FROM TIME TO TIME ?"

TNS




I heard once that it was something to do with a build up of gas that 'pops'....but knowing my history of answering these questions I'm bound to be wrong......hmmm...defeatist or what ?

'Men are the same as women...just inside out !'
Title: Re: Question of the Week - Old Version
Post by: DrPhil on 07/12/2004 20:45:20
joint surrounded by fluid
overextending joint = decrease in pressure
decrease in pressure = cavitation
cavitation = bubbles
bubbles burst = noise
Title: Re: Question of the Week - Old Version
Post by: NakedScientist on 18/12/2004 11:48:57
ANSWER TO LAST WEEK'S QOTW :

"WHAT MAKES YOUR JOINTS 'CRACK' FROM TIME TO TIME ?"

Dr. Phil has the correct answer. Joints are mobile articulations between bones. The ends of the bones are covered by a slippery layer of cartilage, rather like anatomical teflon, which is lubricated by a thin liquid called synovial fluid. The joint is enclosed by membranes and supporting tissues that retain and maintain the fluid, stabilise the joint, and also help to determine the directions in which it can move.

Because the fluid is held within an enclosed space, when the joint moves in certain directions it sometimes squashes the fluid on one side of the joint, and creates a partial vaccuum in the fluid on the other side of the joint.

Just as water boils at a lower temperature at the top of a mountain because the atmospheric pressure is lower at altitude, lowering the pressure in joint fluid causes small vapour bubbles to form (from the water in the synovial fluid). When these bubbles then subsequently collapse on themselves again they do so with a 'pop', which is the sound you hear.

This process is referred to as 'cavitation', and is responsible for the 'pitting' effect you see on boat propellers and hydrofoils. When the propeller cuts the water it creates zones of low pressure which yield vapour bubbles. The collapse of these bubbles against the propeller surface releases energy which damages the blades.

Fortunately for us, it happens too infrequently to cause harm to our joints !

TNS
Title: Re: Question of the Week - Old Version
Post by: NakedScientist on 18/12/2004 11:53:24
HERE'S THIS WEEK'S QOTW :

"WHY DOES ICE FLOAT, WHEN MOST SOLIDS ARE HEAVIER THAN LIQUIDS ?"

TNS
Title: Re: Question of the Week - Old Version
Post by: neilep on 18/12/2004 13:13:10
cos water is well weird and when it feezes it becomes less dense than liquid water... i know something strange happens at 4 degrees C, something do do with a crystal lattice and hydrogen ......and HEY !!!... I kind of got the above  (joints cracking etc)question partially right in my own way.....HMMMPTHH !!!


'Men are the same as women...just inside out !'
Title: Re: Question of the Week - Old Version
Post by: gsmollin on 21/12/2004 21:28:24
Yea, Neil just can't get no respect. He hits the buzzer first and credit goes to some guy with a "Dr" moniker. Maybe if he put his answer in the form of a question...
Title: Re: Question of the Week - Old Version
Post by: neilep on 21/12/2004 21:44:48
quote:
Originally posted by gsmollin

Yea, Neil just can't get no respect. He hits the buzzer first and credit goes to some guy with a "Dr" moniker. Maybe if he put his answer in the form of a question...



Thanks for the support gsmollin !!...I feel so neglected sometimes [;)]!!...but you've cheered me up...thanks.....

'Men are the same as women...just inside out !'
Title: Re: Question of the Week - Old Version
Post by: tups on 06/01/2005 15:21:10
Water in its liquid form forms networks and chains of water molecules that are connected together by hydorgen bonds, a kind of chemical bond in which a hydrogen atom is "shared" between two more electronegative atoms. Water always does a balance act : on the one hand thermal motion makes the networks smaller and expands the volume a single water molecule needs, ie regular thermal expansion. However, in an ideal network, every water molecule binds to two others with its hydrogen atoms, and accepts bonds from two more water molecules, and so forms a tetrahedric structure, which is very loosely packed, has, in other words, quite large holes in it. This ideal lattice is solid crystalline ice. It is thus less dense than when the networks break down into smaller and smaller chunks. The maximum density is reached at 4 degrees, where decreased networking starts to be offset by thermal expansion.
And that's the story of water. If it didn't form such a weird crystal structure, ice wouldn't float, oceans would regularly have frozen completely during the history of earth, and we wouldn't be alive today.
Lucky us ... :-)

tups
Title: Re: Question of the Week - Old Version
Post by: Donnah on 20/01/2005 04:17:01
quote:
Originally posted by NakedScientist

ANSWER TO LAST WEEK'S QOTW :

"WHAT MAKES YOUR JOINTS 'CRACK' FROM TIME TO TIME ?"

Dr. Phil has the correct answer. Joints are mobile articulations between bones. The ends of the bones are covered by a slippery layer of cartilage, rather like anatomical teflon, which is lubricated by a thin liquid called synovial fluid. The joint is enclosed by membranes and supporting tissues that retain and maintain the fluid, stabilise the joint, and also help to determine the directions in which it can move.

Because the fluid is held within an enclosed space, when the joint moves in certain directions it sometimes squashes the fluid on one side of the joint, and creates a partial vaccuum in the fluid on the other side of the joint.

Just as water boils at a lower temperature at the top of a mountain because the atmospheric pressure is lower at altitude, lowering the pressure in joint fluid causes small vapour bubbles to form (from the water in the synovial fluid). When these bubbles then subsequently collapse on themselves again they do so with a 'pop', which is the sound you hear.

This process is referred to as 'cavitation', and is responsible for the 'pitting' effect you see on boat propellers and hydrofoils. When the propeller cuts the water it creates zones of low pressure which yield vapour bubbles. The collapse of these bubbles against the propeller surface releases energy which damages the blades.

Fortunately for us, it happens too infrequently to cause harm to our joints !

TNS
Does that mean that someone whose joints crack every time they bend them is more likely to have joint problems later in life?

"Remember, if you ever need a helping hand, you will find one at the end of each of your arms." - Audrey Hepburn
Title: Re: Question of the Week - Old Version
Post by: chris on 20/01/2005 08:40:18
I haven't heard any evidence that cracking joints are more prone to arthritis later in life, but I'll look into that.

Chris

"I never forget a face, but in your case I'll make an exception"
 - Groucho Marx
Title: Re: Question of the Week - Old Version
Post by: NakedScientist on 28/01/2005 09:16:57
ANSWER TO "WHY DOES ICE FLOAT, WHEN MOST SOLIDS ARE HEAVIER THAN LIQUIDS ?"

Tups and Neil have this correct.

Water molecules resemble tiny boomerangs with an oxygen atom at the centre, and 2 hydrogens for arms. Because the oxygen likes electrons it pulls the electrons of the hydrogen atoms towards it, making the arms of the boomerang slightly positive, and the oxygen slightly negative.

This makes the molecules 'sticky' due to a process called hydrogen bonding. The slightly positive hydrogen from one water molecule is attracted to the slightly negative oxygen of another water molecule, and the 2 try to get closer together.

As you cool down water, the molecules lose energy, slow down, and can pack together more tightly. At 4 degrees C the molecules are at their most tightly packed.

But if you lower the temperature further it becomes more energetically favourable for the water molecules to arrange themselves into a more open tetrahedral lattice, in which each water molecule has a relationship with 4 others.

This configuration, rather like Swiss cheese, has lots of holes between the molecules and so the only way to pack in all the water molecules as freezing occurs is to make a crystal that takes up more volume than the starting liquid.

So why does it float ?

This is down to the Archimedes principle. When you place an object in water it displaces a volume of water equivalent to its weight. In other words water molecules push upwards on it with a force equal to the weight of the water that has pushed out of the way (displaced).

As ice is 'holey', as outlined above, it is much less dense than liquid water (about 9% less dense in fact) meaning that it doesn't have to sink very far before it has displaced enough water to support itself (because the deeper you go the higher the pressure and hence the higher the density).

As a result ice floats - thankfully - otherwise fish would be in real trouble, and the floors of our oceans would be covered with ice...

TNS
Title: Re: Question of the Week - Old Version
Post by: NakedScientist on 28/01/2005 09:22:11
Here's this week's QOTW

"HOW DO WE KNOW HOW FAR IT IS TO DISTANT GALAXIES - SUCH AS THE ANDROMEDA GALAXY WHICH IS 3 MILLION LIGHT YEARS AWAY ?"
Title: Re: Question of the Week - Old Version
Post by: nilmot on 28/01/2005 09:31:27
Just some chemistry fact about what 'NakedScientist' said above.

'The oxygen likes electron bit', the technical term is electronegative. Definition is the ability for a covalently bonded atom to draw a pair of electron toward itself. I think saying likes electron can be slightly misleading, some might mis-interpret it thinking atoms have preference to which electrons they like.

Tom
Title: Re: Question of the Week - Old Version
Post by: neilep on 28/01/2005 11:29:25
I won't answer this cos I'm proud to say I know the answer thanks to Dr Chris and Radio 5 Live :-)

'Men are the same as women...just inside out !'
Title: Re: Question of the Week - Old Version
Post by: NakedScientist on 08/02/2005 13:05:27
I'm sad that no one wants to have a go at this week's QOTW...[:(]
Title: Re: Question of the Week - Old Version
Post by: Ultima on 08/02/2005 13:19:22
Erm... Don't you take an observable object with known brightness within the Galaxy such as a supernova or I remember something about Cepheid Variables that have fixed intensity for their period which you can use, then using loads of rules of distance r and light intensity etc. you can work out the rough distance??? Or is this just rubbish? I'm guessing... my Astronomy module was a while ago [:D]

wOw the world spins?
Title: Re: Question of the Week - Old Version
Post by: nilmot on 10/02/2005 08:55:09
Is it the Red Shift...?

My physic is really bad I have to say

Tom
Title: Re: Question of the Week - Old Version
Post by: DrPhil on 12/02/2005 13:14:19
I agree with Ultima. Back in the olden days (early 1900s) the luminosity of Cepheids was used as a yardstick, unfortunately they are not bright enough to be seen beyond our local galaxies. Now, the apparent brightness of the Type Ia supernova is used to determine distances to galaxies billions of light-years from earth. Last year astronomers discovered a pattern in the energy emitted by gamma-ray bursts which they believe could help them map the most distant parts of the cosmos.
Title: Re: Question of the Week - Old Version
Post by: gsmollin on 18/02/2005 16:52:05
quote:
Originally posted by NakedScientist

I'm sad that no one wants to have a go at this week's QOTW...[:(]



I was inattentive, since the "question of the week" never comes out weekly, so I missed this week's (month's?) QOTW...

Historically, the Cepheid variables were used as brightness standards to show that the stars in the galaxy in Andromeda were much further away than thought before the time of Edwin Hubble. I believe the Cepheids were calibrated using parallax methods, although I should be checking my history before I make that claim. Hubble was then able to calibrate the red shift of the spectrum in the Cepheids, and showed the correlation between that and the distance. He then applied the red-shift-distance correlation to very distant galaxies, and determined they were billions of light years away. Of course, the red-shift-distance correlation factor became known as Hubble's constant, and has been refined since that time.

Later: According to the history, the Cepheid variables are named after the star Delta Cephei, which were studied by Henrietta Leavitt. D. Cephei is close enough to use a parallax measurement for its distance. With that, plus a knowledge of the period-absolute magnitude relationship in the Cepheid variables, Leavitt used the Cepheid variables to measure the distance to the Small Magellanic Cloud.
Title: Re: Question of the Week - Old Version
Post by: simeonie on 29/07/2005 12:51:29
if we had wings and a really strong chest could we fly?

----------------------
-__- my website!!!!
http://www.simeonie.co.uk
has forums too!
Think about it! lolz
Title: Re: Question of the Week - Old Version
Post by: ukmicky on 29/07/2005 20:18:54
simeonie

I dont think so, human bones are to heavy and not flexible enough.
Title: Re: Question of the Week - Old Version
Post by: neilep on 29/07/2005 23:56:36
quote:
Originally posted by simeonie

if we had wings and a really strong chest could we fly?

----------------------
-__- my website!!!!
http://www.simeonie.co.uk
has forums too!
Think about it! lolz


Well..I presume if we had a strong chest and wings we'd also have very strong other bits to compensate !!...and if we had feathers and a beak..we'd all be birdies too !!

(https://www.thenakedscientists.com/forum/proxy.php?request=http%3A%2F%2Finstagiber.net%2Fsmiliesdotcom%2Fcontrib%2Ficw%2F003.gif&hash=f326f525e3f6c60d4ea3ecbb24d1df2a)Men are the same as women.... just inside out !!(https://www.thenakedscientists.com/forum/proxy.php?request=http%3A%2F%2Finstagiber.net%2Fsmiliesdotcom%2Fcontrib%2Ficw%2F003.gif&hash=f326f525e3f6c60d4ea3ecbb24d1df2a)
Title: Re: Question of the Week - Old Version
Post by: Tronix on 03/08/2005 20:32:58
im sure we could fly, but the wing span would be huge (remember the ptersaur?). Unless we had jet packs. come to think of it, we fly every day (and the wing span IS huge)...

--------------------------------------------
"If i cannot have company whose minds are clearly free, I would prefer to go alone."                  -Dr. Gideon Lincecum

The BPRD rejected my application becuase their brain-controled by Cthulhu Rip-offs. And im sure "Sparky" is sleeping with them too, kinky little firecracker she is...
Title: Re: Question of the Week - Old Version
Post by: spade23 on 20/08/2005 00:05:49
I think that that is a brilliant idea.[:D][:D][:D]


 (http://) |  (http://) |  (http://) |
Title: Re: Question of the Week - Old Version
Post by: saanwal on 21/08/2005 16:55:13
Dear Scientists
 
I want to know how much ozone layer is now left?
 
Please tell me.
 
Thanks

Saanwal.
Title: Re: Question of the Week - Old Version
Post by: Razor on 21/08/2005 18:46:26
quote:
Originally posted by saanwal

Dear Scientists
 
I want to know how much ozone layer is now left?
 
Please tell me.
 
Thanks

Saanwal.



Well im not sure "how much" ozone layer is left but this website should help you to answer your question:
http://www.nasa.gov/vision/earth/lookingatearth/25TOMSAGU.html


-----------------------
"We apologize for the error in last week's paper
In which we stated that Mr. Arnold Dogbody was a defective in the police force. We meant, of course, that Mr. Dogbody is a detective in the police farce."
-Correction notice in the Ely Standard, a British newspaper

For those who havenít seen this yet, it's a must view!!!!
CHECK IT OUT!!!!

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Also:
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For Dodge Viper Fans.
Title: Re: Question of the Week - Old Version
Post by: aasurfer33 on 24/09/2005 07:45:30
Hey really of the topic, but what does everyone on this post and the Dr. think the best college to go to for science in the states or anywhere else.
Title: Re: Question of the Week - Old Version
Post by: pyromaster222 on 15/10/2005 20:22:30
the distance to other galaxies is measured by the dopler effect (or red shift) this is when galaxies move away from each other and is caused by light waves being "stretched" towards the red spectrum of light. Therefore the light has a reddish tint when observed. The severity of the red shift tells us how far away the galaxy is because the further a galaxy is from ours the faster its moving away, due to the fact that the universe is expanding in all directions at once.
Title: Re: Question of the Week - Old Version
Post by: NakedScientist on 04/11/2005 18:04:22
QOTW RETURNS !

To kick off a new series of "Question of The Week", have a go at this week's 'poser' :

- WHAT STOPS METAL BOATS (MADE OF IRON) FROM GOING RUSTY ?

Have a go below, answer next week.

TNS
Title: Re: Question of the Week - Old Version
Post by: neilep on 04/11/2005 18:15:59
Do they put a sign on it that says ' No Rust Allowed ' ?...because if I was a bit of rust that would stop me !...or is just some Anti-rust paint  ?

Men are the same as women.... just inside out !! (https://www.thenakedscientists.com/forum/proxy.php?request=http%3A%2F%2Fwww.world-of-smilies.com%2Fhtml%2Fimages%2Fsmilies%2Fparty%2Fballoons.gif&hash=f9f40e7ab655ca9089398c3f3719f593)
Title: Re: Question of the Week - Old Version
Post by: ukmicky on 04/11/2005 23:46:52
Canít remember what their called or how exactly they work, but donít they place special metal blocks under the ship which when given a charge attract the electrons released by the interaction of the salt water on iron, causing the metal blocks to rust rather than the ship. Or something like that[:)]

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Title: Re: Question of the Week - Old Version
Post by: pyromaster222 on 12/11/2005 21:02:59
they have a magnesium or zinc block attatched to the boat. the magnesium or zinc is more reactive than iron and so is sacrificed and therefore reacts with the sea water rather than the iron. this means the iron stays rust free. this process is also used in galvinisation of fences etc. but the term galvinised is referred to objects covered in zinc..not any other metal.
Title: Re: Question of the Week - Old Version
Post by: DrN on 20/11/2005 22:56:36
ah yes - I remember something about a zinc (or somethng) block attached to the sewage pipe to stop that rusting. obviously it would be minor disaster (and not just to the blue flag status of the beach) if that got holes in it. so it must work I guess.
Title: Re: Question of the Week - Old Version
Post by: chris on 20/12/2005 08:57:19
ANSWER TO "WHAT STOPS METAL BOATS (MADE OF IRON) FROM GOING RUSTY ?"

You're right. Apart from a coat of paint, corrosion of the metallic parts of boats, pipes and oilrigs can be reduced by sacrificial protection. Put simply, by connecting a more reactive metal to a piece of iron - either by direct attachment, or even with cables, the more reactive metal sacrifices itself to prevent the iron from oxidising. This is analogous to a displacement reaction with electrons passing from the more reactive metal to the iron. Usually zinc (galvanising), or magnesium, are used and are referred to as "sacrificial anodes".

The chemical reaction is :

3Zn -> 3Zn++ + 6e-
2Fe+++ + 6e- -> 2Fe

In other words, the zinc (or magnesium) is oxidised (and dissolves) instead of the iron. The process will work as long as the two metals are electrically connected and in contact with the electrolyte. In the long run it's cheaper to replace the anode several times than to replace the boat !

Chris

"I never forget a face, but in your case I'll make an exception"
 - Groucho Marx
Title: Re: Question of the Week - Old Version
Post by: chris on 20/12/2005 08:58:32
Here's this week's Festive Christmas QOTW to mull over whilst enjoying your mince pies and port :

"WHAT IS HEAVY WATER AND WHY IS IT USEFUL ?"

Merry Christmas.

Chris

"I never forget a face, but in your case I'll make an exception"
 - Groucho Marx
Title: Re: Question of the Week - Old Version
Post by: Soul Surfer on 21/12/2005 10:50:58
OK I've left this to sit for 24 hours.  Heavy water is duterium oxide the combination of oxygen with the other stable isotope of Hydrogen duterium which has a neucleus of a single protn and a single neutron  it exists in water to a tiny proprtion and can be sperated by fractional distillation or electroysis.

Its main use is as a moderator in nuclear fission reactors using U235 because it is quite good slowing down the neutrons produced in the fission fron high speeds to "thermal" neutrons (thus extracting the energy of the reaction)the fission chain reaction in U235 will operate with thermal neutrons.  Using a moderator also renders the reaction more controllable by slowing the rates at which things can run away allowing it to be controlled with mechanical devices.

Learn, create, test and tell
evolution rules in all things
God says so!
Title: Re: Question of the Week - Old Version
Post by: Bass on 02/01/2006 22:19:03
I have this dim memory, eons ago, that ducks can't float on heavy water??
Any truth to this, or just another myth?

Subduction causes orogeny.
Title: Re: Question of the Week - Old Version
Post by: DoctorBeaver on 02/01/2006 22:31:26
quote:
I have this dim memory, eons ago, that ducks can't float on heavy water??
Any truth to this, or just another myth?


That's because they're witches (Monty Python fans may understand that)
[:D]
Title: Re: Question of the Week - Old Version
Post by: neilep on 02/01/2006 23:09:57
I wonder of we should change the name of this thread from Question Of The Week to Question Of The Whenever !![;)]

Men are the same as women.... just inside out !!
Title: Re: Question of the Week - Old Version
Post by: DoctorBeaver on 02/01/2006 23:19:30
Questions from the stone-age[:D]
Title: Re: Question of the Week - Old Version
Post by: chris on 09/01/2006 11:19:28
Give me a break you lot.

My new year resolution is to ensure that we have a high quality QOTW each week from henceforth.

We'll start from today and I'll post the question shortly.

Chris

"I never forget a face, but in your case I'll make an exception"
 - Groucho Marx
Title: Re: Question of the Week - Old Version
Post by: DoctorBeaver on 09/01/2006 16:48:45
*looks at watch* 5 and a half hours later... zzzzzzzzzzz
Title: Re: Question of the Week - Old Version
Post by: neilep on 09/01/2006 18:59:42
...hey !!..this a good idea...question Of the Week eh ?...it might actually catch on !

Men are the same as women.... just inside out !!
Title: Re: Question of the Week - Old Version
Post by: DoctorBeaver on 09/01/2006 22:47:03
Make that 11 and a half
Title: Re: Question of the Week - Old Version
Post by: ukmicky on 09/01/2006 23:06:46
Give him a chance he's a doctor, and if he's anything like mine he's busy congratulating his patients on catching the flu and them telling them to go away and to let it run its course.

so you then go away and get a chest infection and when you go back the doctor say's arrhh you've now got a chest infection, now go away and let it run its course.

I can do that, maybe i should be a doctor

Sorry chris i know your a good doctor really[:)]

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Title: Re: Question of the Week - Old Version
Post by: ukmicky on 10/01/2006 01:16:38
Question

Why do we never get to see the dark side of the moon



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Title: Re: Question of the Week - Old Version
Post by: neilep on 10/01/2006 01:40:38
Gosh !! i'm dumbfounded...I actually know the answer to this but seeing as Michael only asked it less than half an hour ago I'll leave it for some of the non vampires to respond to.

Men are the same as women.... just inside out !!
Title: Re: Question of the Week - Old Version
Post by: DoctorBeaver on 10/01/2006 02:11:26
I think you've asked either a wrong question or a trick 1.
I suspect the answer you want is that as the moon's period of rotation is the same as the time it takes to orbit the Earth, the same side is always facing us.
However, even if the 2 periods were different so that we could actually see the moon rotating on its axis, we would still never see "the dark side" as we could only ever see whichever part of the moon was facing the Earth.
In any case, at new moon even the side that is facing us is dark & we can still see that with light amplifying equipment.

Pedants rule! [:p]
Title: Re: Question of the Week - Old Version
Post by: ukmicky on 10/01/2006 02:38:23
Damn your good.



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Title: Re: Question of the Week - Old Version
Post by: DoctorBeaver on 10/01/2006 02:58:12
quote:
Damn your good.


That's what she said last night [:D]
But she was talking about my cooking [:(]
Title: Re: Question of the Week - Old Version
Post by: ukmicky on 10/01/2006 03:40:30
I  think its weird how the one species of life on earth since its creation which is able to appreciate an eclipse of the sun happens to be around at the best time to view it. if we were around much earlier in the history of the earth the moon would be closer and cover too much up and much later and the moon will be further away from the earth and not cover up enough.
At present time the moon  400 x nearer than the Sun with a radius which is 400 x smaller than the sun. WEIRD
At present time the moon also rotates once  every time it orbits the earth , so we always get the same view THAT'S ALSO WEIRD


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Title: Re: Question of the Week - Old Version
Post by: chris on 10/01/2006 09:53:52
I've seen Dark Side of the Moon. In fact I'm looking at it now, alongside "Momentary Lapse of Reason" and "The Final Cut".

Sorry about the lack of a question last night. My computer actually decided to die at 4.30. Nice.

Anyway, I think ukmicky's question about the dark side of the moon is actually excellent, so let's kick off with that, and I'll save my question for next week.

Chris

"I never forget a face, but in your case I'll make an exception"
 - Groucho Marx
Title: Re: Question of the Week - Old Version
Post by: DoctorBeaver on 11/01/2006 01:37:11
What a cop out! [:o)]
Title: Re: Question of the Week - Old Version
Post by: chris on 15/01/2006 14:46:46
Here's this week's QOTW (and this time there will be a weekly turnover of questions):

"WHY DO WE SEE OUR BREATH ON COLD DAYS ?"

Have a go, below...

Chris

"I never forget a face, but in your case I'll make an exception"
 - Groucho Marx
Title: Re: Question of the Week - Old Version
Post by: DoctorBeaver on 15/01/2006 15:45:02
That's easy. (but don't ask Blunkett) [:o)]
Title: Re: Question of the Week - Old Version
Post by: chris on 15/01/2006 21:41:57
Come on then, let's see the answer...

"I never forget a face, but in your case I'll make an exception"
 - Groucho Marx
Title: Re: Question of the Week - Old Version
Post by: DoctorBeaver on 16/01/2006 20:58:21
Temperature difference blah blah condensation blah [:p]
Title: Re: Question of the Week - Old Version
Post by: DoctorBeaver on 16/01/2006 21:00:39
Actually, to answer your question, we can see it because it's visible. The question should really have been "Why is it visible?"
Title: Re: Question of the Week - Old Version
Post by: ukmicky on 17/01/2006 01:58:16
quote:
The question should really have been "Why is it visible?"


Because we have eyes

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Title: Re: Question of the Week - Old Version
Post by: DoctorBeaver on 17/01/2006 04:13:15
No, Michael. We can see it because it's visible and we have eyes. Moles can't see it, but it must be visible as we can percieve it. Therefore, we can see it as it's visible to us.
But Chris, I believe, is after the process that makes it visible; which is a different question.

Jeez - I'm still good! [:D] Do I get my TNS pedant award now?
Title: Re: Question of the Week - Old Version
Post by: ukmicky on 17/01/2006 04:25:14
Are but what do you define as visible,rats have ultraviolet vision so is that visible.just because we cant see it dosent mean its not visible[:D]

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Title: Re: Question of the Week - Old Version
Post by: DoctorBeaver on 17/01/2006 04:33:15
Absolutely, Michael. I would say something is visible if it can be detected by any creature's optical sensing mechanism or an enhancement therefore e.g. a microscope or telescope.
Title: Re: Question of the Week - Old Version
Post by: chris on 17/01/2006 12:57:00
Why is it visible on a cold day, but not on a hot day ?

Chris

"I never forget a face, but in your case I'll make an exception"
 - Groucho Marx
Title: Re: Question of the Week - Old Version
Post by: ariel on 17/01/2006 19:15:03
The moisture in warm air you exhale is chilled and condensed when it reaches cold air- so its visible like fog!
when its hot outside...it isn't chilled, and doesn't condense- so its not visible not like fog!
Title: Re: Question of the Week - Old Version
Post by: DoctorBeaver on 17/01/2006 19:40:51
I refer the honourable gentleman to the answer I gave some moments ago [:D]
Title: Re: Question of the Week - Old Version
Post by: ariel on 18/01/2006 21:40:30
psh, if you're referring to me..im not a gentleman :-)
Title: Re: Question of the Week - Old Version
Post by: rosy on 18/01/2006 21:45:44
The bit everyone's already said:
Air cools, the amount of water it will hold decreases, some of the water condenses out and forms droplets.
Now, the bit that actually answers the question:
The droplets of water have a different refractive index to air, so light is bent through the droplets and what you see through them is not the same as you'd see through the patch of air they've replaced.
Title: Re: Question of the Week - Old Version
Post by: DoctorBeaver on 19/01/2006 11:05:41
Ariel - It was to Chris, not you
Title: Re: Question of the Week - Old Version
Post by: ariel on 20/01/2006 00:20:51
yay
Title: Re: Question of the Week - Old Version
Post by: chris on 20/01/2006 16:52:24
quote:
Originally posted by rosy

The bit everyone's already said:
Air cools, the amount of water it will hold decreases, some of the water condenses out and forms droplets.
Now, the bit that actually answers the question:
The droplets of water have a different refractive index to air, so light is bent through the droplets and what you see through them is not the same as you'd see through the patch of air they've replaced.



"I never forget a face, but in your case I'll make an exception"
 - Groucho Marx
Title: Re: Question of the Week - Old Version
Post by: chris on 29/01/2006 16:20:18
Here's the answer to last week's QOTW :

"WHY DO WE SEE OUR BREATH ON COLD DAYS ?"

This was a trick because there were several parts to the answer. Rosy was the closest. No one, for instance, mentioned why our breathe was damper than the air we inhaled...

Here's the answer:

We use our lungs to pick up oxygen from the air we breathe in, and to expel carbon dioxide, a waste product. This process occurs in a system of tiny air sacs called "alveoli" which give the lungs, when viewed up close, the appearance of a piece of sponge. The surfaces of the alveoli are kept moist to facilitate the exchange of gases between the blood and the airspaces.

Because the alveolar surfaces and the trachea, mouth and nasal passages are moist the air we breathe out picks up water and leaves the body at 37 degrees C (body temperature) and 100% humidity. If you add up how much water a person breathes out in a day it's almost half a litre (400 ml). This is referred to as "insensible losses".

When you breathe out this water-laden air, it immediately begins to cool and as it does so it becomes easier for molecules of water vapour (H2O) to cling together. If the air around you is sufficiently cold your breath cools very rapidly, and the water molecules quickly glue themselves together to form tiny water droplets. These droplets behave like miniature lenses, bending the light passing through them and thereby making them visible.

This doesn't happen on a hot day because the ambient air is warm enough to keep the water molecules zipping around freely - in other words they can't cling to each other to form droplets - and so your water-soaked breath remains invisible...

Chris



"I never forget a face, but in your case I'll make an exception"
 - Groucho Marx
Title: Re: Question of the Week - Old Version
Post by: chris on 29/01/2006 16:21:48
Right, since I'm on a roll, here's this week's QOTW:

"WHAT ARE RADIO WAVES, AND HOW ARE THEY PRODUCED AND RECEIVED?"

Have a go, below.

"I never forget a face, but in your case I'll make an exception"
 - Groucho Marx
Title: Re: Question of the Week - Old Version
Post by: Soul Surfer on 29/01/2006 19:37:59
Radio waves are part of the lower frequency end of the electromagnetic spectrum which includes microwaves,infra red,light ultra violet, X rays and gamma rays as well as long medium and short radio waves.

The simple way to understand them is by remembering that a changing electrical field or cuurent flowing will produce a magnetic field and a changing magnetic field will produce an electric field and this can go on even through a vacuum with no other physical structures involved.  they travel as waves at the velocity of light in a vacuum but in solids liquids and gases that are non conducting (they travel a bit slower.  conducting surfaces short out the induced currents and cause the waves to be reflected.  Light travels at 300,000 Km/sec so a low frequency radio wave with about 300 Khz is about 1km long.  (remember for any wave motion frequency times wavelenth = the velocity of the wave) The most familiar radio waves are the medium frequency waves at about 1Mhz (wavelength abouut 300 meteres) and Ultra high frequency television waves at about 500MHz  (wavelength 3/5 metre or 60cm.

Now as these waves propagate through space the cause voltages to appear across and currents to flow between  beteween points seperated by half a wavelength and a good way of detecting and launcing them is to have electrical conductors in pairs a quarter of a wavelength long to detect or launch the waves  (a half wave dipole) The process of detecting or launcing these waves is essentially symmetrical in that good structures to detect them are good structures to launch them.

To launch them you just need to generate an alternating current at the required frequency and apply it to the half wave dipole.  At very low frequencies it is possible to do this with an electrical generator but most RF generators require the use of an electromagnetic tuned cucuit coupled to an amplifier to create an oscillator.

An electromagnetic tuned ciruit consists of a capacitor that will store electrical charge when a voltage is applied (a bit like a battery) an inductor is a bit like an electromagnet which generates a magnetic field when a current flows through it.  If you connect them together in series or in parallel and the  the charge in the capacitor chn discharge through the coil and create a magnetic field and when the charge runs out the collapsing magnetic field can recharge the capacitor so they resonate a bit tlike a weight dangling from a spring after you pull it down.

coupling a resonant circuit to an amplifier using an electrobic device like a transisto alolows you to amlify any signals induced by radio waves in your half wave dipole or alternatively if you connect the output of the amplifier back to its input through the tuned circuit so that the sigtnal is fed back in phase with the  input it will osscillate at the resonant frequency of the circuit.

Now all this is going on at millions of cycles per second and you want to see something tthat you can understand to kniow that you have detected some radio waves so you need to turn the AC signal into DC which you can detect usinf a meter.  To do this you put a diode which is a device that allows electrical current to flow one way but not the other and thus gives you a signal when some radio waves are detected

In its simplest form you can transmit and detect you radio waves by switcing your transmitter on and off and detecting the level chage using your diode receiver but you can do it much faster than this using electronics.  Sensdin amplitude modulated audio sinmals or coded amplidude modulated signals to create pictures when they are arranged in lines to form television.

Unfortunately amplitude modulated signals are very subject to interference because any other signals at a similar frequency will mess them up so techniques to frequency or even phase modulate the signals are now more standard.

Learn, create, test and tell
evolution rules in all things
God says so!
Title: Re: Question of the Week - Old Version
Post by: ukmicky on 29/01/2006 21:10:49
Hi Ian or anyone

How wide is the gamma frequency part of the EM spectrum,does it go on for ever .
I know its the shortest wavelenght but could there be undiscovered frequencies beyond gamma with properties we cant detect yet and therefore if found would be clasified as something diferent to GAMMA[:)]

Michael                 HAPPY NEW YEAR                     (https://www.thenakedscientists.com/forum/proxy.php?request=http%3A%2F%2Fi11.photobucket.com%2Falbums%2Fa186%2Fukmicky%2Fparty-smiley-012.gif&hash=844994fd61764508c533537d6874634d)
Title: Re: Question of the Week - Old Version
Post by: Soul Surfer on 29/01/2006 23:34:23
In general gamma rays go right up to the limit which is when the photon gets so energetic it turns into a black hole!

Not quite sure where the limit between xrays and gamma rays is  probably somewhere around 1Mev.

Just checked one rather old reference and it suggesed that X-rays and gamma rays overlapped a bit and that X-rays were produced by violently stopping electrons as in an X-ray tube but gamma rays were photons originating from nuclear reactions ie coming from an excited nucleus.

Another more modern reference suggested gamma rays tarted at wavelengths less than 0.1nm  and frequencies in excess of 10^18 Hz

There is really not much need for any distinction above the threshold for gamma rays because except for the fact that the photons get more and more energetic their general properties remain much the same and there are no gaps in knowledge right up to the limit of the highes energy cosmic rays.

Learn, create, test and tell
evolution rules in all things
God says so!
Title: Re: Question of the Week - Old Version
Post by: ukmicky on 30/01/2006 01:23:12
Cheers ian. It was something that i've always wondered.

I couldnt see any reason why the EM spectrum couldnt go on forever and into wavelenths  which we couldnt detect as yet

Michael                 HAPPY NEW YEAR                     (https://www.thenakedscientists.com/forum/proxy.php?request=http%3A%2F%2Fi11.photobucket.com%2Falbums%2Fa186%2Fukmicky%2Fparty-smiley-012.gif&hash=844994fd61764508c533537d6874634d)
Title: Re: Question of the Week - Old Version
Post by: ScooterTrash on 05/02/2006 03:37:01
quote:
Originally posted by NakedScientist

ANSWER TO "HOW DOES GLOW IN THE DARK PLASTIC WORK AND WHAT MAKES THE HANDS ON WATCHES GLOW"

The answers given above are pretty much correct.

Things that glow in the dark are referred to as 'phosphors' and are materials which can soak up energy and then re-radiate it as visible light. Put simply, when these substances absorb energy (in the form of light, heat or radiation) some of their electrons become excited and are catapulted up to a higher energy state. Light is emitted (and the substance glows) when the excited electrons fall back to their 'ground state', releasing the extra energy that they picked up previously.

Television screens (the non-LCD / Plasma screen variety) and fluorescent tubes (strip lights) rely on precisely this effect. In a TV the screen is coated with a phosphor which is excited by a stream of electrons produced by a cathode ray gun at the back of the set. In a strip light the electricity excites electrons in the atoms of the metallic element mercury. The excited mercury atoms emit ultraviolet light which hits the phosphor coating on the glass of the tube, which in turn then emits visible (white) light.

The phosphors used in glow in the dark stickers and badges, clock and watch faces commonly contain the compounds zinc sulphide (often with some copper mixed in too) or strontium aluminate. These substances are added to the polymer used to make the plastic. They produce a soft green glow which can, with the correct engineering, persist for minutes to hours.

Another way to make things glow in the dark, but without them needing to be 'charged up' by prior exposure to light, is to use a long-lived radioactive substance, such as radium. The radioactive material can be combined with an appropriate phosphor which is excited by the radioactivity and converts the energy of the radiation into visible light - making the hands of the clock or watch glow.

So, in summary, cheaper clocks and watches use phosphors which soak up light and then release it very slowly to make their hands glow for several hours afterwards. More expensive (and military) timepieces rely on a radioactive substance to energise the phosphor so that they can glow continuously.

Title: Re: Question of the Week - Old Version
Post by: ScooterTrash on 05/02/2006 04:15:33
Whoops!
Sorry for the double-post! I'm new...
(It sucks havin a small brain)
Anyhow, I found this post, an was hoping someone here could shed some light on what might be sheddin light on the phosphourescent buttons of my remote control.
There was a storm here last night and the power went out. I was in the dark for several hours and noticed that the glow-in-the-dark buttons were flashing. The flashing was somewhat random, and continued all night. The plastic glow-in-the-dark stars on my bedroom celing were also brightly flashing. Normally the photon energy has been released from the phosphor after a few minutes, but this went on for a couple hours.
There was a distant lightning storm and I was wondering if that might have been the source of the radiation?
What frequencies of light are absorbed by this stuff?
I know that radium will cause this phosphor to glow, and I was wondering if possibly Radon or some other element may have been the source.
I thought that since I live near the water that perhaps a marine or aircraft radar might have been the source so I put one of the glow-in-the-dark stars in my microwave for a few seconds. (thinking that my microwave was close to the same frequency as Radar.)...
No significant results.
Next I used an infra-red LED; It DID in fact light the star.
Could ionizing radiation frequencies cause the phosphor to blink?
I'm interested in this because I live very close to a nuclear submarine base.
Thanks in advance.


quote:
Originally posted by NakedScientist

ANSWER TO "HOW DOES GLOW IN THE DARK PLASTIC WORK AND WHAT MAKES THE HANDS ON WATCHES GLOW"

The answers given above are pretty much correct.

Things that glow in the dark are referred to as 'phosphors' and are materials which can soak up energy and then re-radiate it as visible light. Put simply, when these substances absorb energy (in the form of light, heat or radiation) some of their electrons become excited and are catapulted up to a higher energy state. Light is emitted (and the substance glows) when the excited electrons fall back to their 'ground state', releasing the extra energy that they picked up previously.

Television screens (the non-LCD / Plasma screen variety) and fluorescent tubes (strip lights) rely on precisely this effect. In a TV the screen is coated with a phosphor which is excited by a stream of electrons produced by a cathode ray gun at the back of the set. In a strip light the electricity excites electrons in the atoms of the metallic element mercury. The excited mercury atoms emit ultraviolet light which hits the phosphor coating on the glass of the tube, which in turn then emits visible (white) light.

The phosphors used in glow in the dark stickers and badges, clock and watch faces commonly contain the compounds zinc sulphide (often with some copper mixed in too) or strontium aluminate. These substances are added to the polymer used to make the plastic. They produce a soft green glow which can, with the correct engineering, persist for minutes to hours.

Another way to make things glow in the dark, but without them needing to be 'charged up' by prior exposure to light, is to use a long-lived radioactive substance, such as radium. The radioactive material can be combined with an appropriate phosphor which is excited by the radioactivity and converts the energy of the radiation into visible light - making the hands of the clock or watch glow.

So, in summary, cheaper clocks and watches use phosphors which soak up light and then release it very slowly to make their hands glow for several hours afterwards. More expensive (and military) timepieces rely on a radioactive substance to energise the phosphor so that they can glow continuously.

Title: Re: Question of the Week - Old Version
Post by: chris on 07/02/2006 17:17:45
There's not much I can add to the highly comprehensive answer already supplied for "What are radio waves etc" by soul surfer. Thank you for saving me a job!

So here's this week's QOTW:

"IF A PERSON SWINGS BACK AND FORTH ON A ROPE, AT WHAT POINT IN THEIR TRAVEL IS THE ROPE SUPPORTING THEM MOST LIKELY TO SNAP?"

Have a go, below...

Chris

"I never forget a face, but in your case I'll make an exception"
 - Groucho Marx
Title: Re: Question of the Week - Old Version
Post by: ukmicky on 07/02/2006 19:37:36
At the bottom of the arc i would have thought.

Michael
Title: Re: Question of the Week - Old Version
Post by: neilep on 07/02/2006 19:52:47
Yes I agree with the maestro because I hear he's a swinger and a part time Tarzan !!....at the bottom of the arc....and if it's not...then it should be !!...

HANG ON !!....just before I press ' submit ' I may feel inclined to change my mind and say it's when the rope is half way between the bottom of the swing and the end of the swing because at that point the person will want to continue going on in a straight line .....and I'm just picturing in my head where I have seen people fall of swinging ropes !!...it's usually half way up the arc..because of Momentum...or is it Inertia ?...it's one of those two...Yes..Momentum will try to yank the person off the rope and snap it at that point....I think.  Say the bottom of the swing is 6 'o' clock and the end of the swing is 3 and 9 'o' clock then the rope will break between 7 and 8 or between 4 and 5.

Men are the same as women.... just inside out !!
Title: Re: Question of the Week - Old Version
Post by: ukmicky on 07/02/2006 20:01:25
No its at the bottom point where the downward motion of the swing suddenly changes to upwards movement creating positive g'forces

Michael
Title: Re: Question of the Week - Old Version
Post by: neilep on 07/02/2006 21:14:52
quote:
Originally posted by ukmicky

No its at the bottom point where the downward motion of the swing suddenly changes to upwards movement creating positive g'forces

Michael




[:D]OK OK Keep your hair on !![:D]...actually I'm about to get my hair shaver and go down Bald Avenue again  !!..

HMmm it seems the rope fairies have misinformed me then....well, i'm guessing anyway but you sound so sure..so..i'm convinced too .....[:D]

Men are the same as women.... just inside out !!
Title: Re: Question of the Week - Old Version
Post by: ukmicky on 07/02/2006 21:19:18
I could be wrong, it has been known

Michael
Title: Re: Question of the Week - Old Version
Post by: DoctorBeaver on 12/02/2006 16:46:19
Most likely at the point where I get out my machete because my friend is filming it for "You've Been Framed" & I want the £100 or however much it is these days. [:D]
Title: Re: Question of the Week - Old Version
Post by: ukmicky on 12/02/2006 16:53:54
Doc your back, nice to see

Michael
Title: Re: Question of the Week - Old Version
Post by: sharkeyandgeorge on 13/02/2006 20:04:08
i have broken many many tarzan swings and 90 percent of the time the rope breaks not at the top of the ark but just as you start to swing back some thing do do with the change in centrifugal force perhaps?

"Defender of the Sea"
Title: Re: Question of the Week - Old Version
Post by: chris on 27/02/2006 17:15:48
Ok, this was a hard one to explain, but here's the solution to:

"AT WHAT POINT IN ITS ARC IS A ROPE SWING MOST LIKELY TO BREAK?"

The simple answer is at bottom dead centre. At this point the kinetic energy of the swing and passenger is at its greatest, and the effect of gravity is acting straight down through the rider on all of his weight. So the swing is most likely to break at the mid point of its travel.

Now for the more complicated proof of concept.

If we consider a swing (and rider) which together have a mass of m suspended on a cord of length L (with negligible mass), swinging through an angle of x degrees (where 0 degrees is the horizontal).

Lets assume that the swing begins held out at 90 degrees i.e. horizontal (admittedly a scary ride!). Starting from this point, the speed of the swing at any point in its subsequent arc of travel will be such that the kinetic energy (0.5 * m * velocity(v) ^ 2) is equal to the change in potential energy from its starting point. The change in potential energy will be:

the mass of the swing and rider(m) * gravity * L * sin(x)

So 0.5 * m * v^2 = m * g * L * sin(x)

hence v^2= m * g * L * sin(x)/0.5 * m

hence v^2= 2 * g * L * sin(x)

Now the pull exerted by the swing on the rope is given by the formula speed squared / radius of arc, or v^2 / L (length of swing rope).

So the pull here is v^2 / L which equals 2 * g * sin(x).

The contribution due to gravity at any point along the travel will be g * sin(x).

Since F (tension in the string)= m * a

then the tension (T) must be m * ((2 * g * sin(x) + g * sin(x))

which equals 3mg sin(x).

So, at any point the tension in the rope supporting the swing will be 3 * mass of swing and rider * sin(angle travelled).

If we substitute into this formula, sin(0) - horizontal - is 0, so at thte start point, when the speed is zero, there is no tension on the rope.

One third of the way to the bottom dead centre (30 degrees), sin(30) = 0.5 so the tension is 3mg * 0.5

Two thirds of the way to the bottom (60 degrees), sin (60) = 0.666667 so the tension is 3mg * 0.666667

And at the bottom (90 degrees), sin (90) = 1 so the tension is 3mg. This is the maximum. So the rope has to be capable of holding three times the rider's weight.

I hope that helps to lay that one to rest.

Chris
Title: Re: Question of the Week - Old Version
Post by: chris on 27/02/2006 17:18:38
Okay, here's this week's QOTW:

"WHAT IS A HOLOGRAM, AND HOW ARE THEY MADE?"

Have a go, below.

"I never forget a face, but in your case I'll make an exception"
 - Groucho Marx
Title: Re: Question of the Week - Old Version
Post by: neilep on 27/02/2006 17:54:04
It's a telegram with no substance whatsoever [:)]



ps: Well done Michael..I reckon you got the ropey question right...with no strings attached of course !! [:)]

Men are the same as women.... just inside out !!
Title: Re: Question of the Week - Old Version
Post by: DoctorBeaver on 28/02/2006 20:24:38
Neil - that was almost bad enough to be mistaken for 1 of mine!

On a serious note, a friend of mine set himself up as a Hollergram. Instead of singing the message to people, he shouted it at them!
Title: Re: Question of the Week - Old Version
Post by: neilep on 01/03/2006 11:24:49
Eth, Mine don't even come close...[:)]

Hollergram .....agghhhhh !!..see ?

Men are the same as women.... just inside out !!
Title: Re: Question of the Week - Old Version
Post by: DoctorBeaver on 01/03/2006 14:11:42
Or what about a Holagram who just says "hello" to you in Spanish?
Title: Re: Question of the Week - Old Version
Post by: Ray hinton on 01/03/2006 15:58:57
or a HALOGRAM,just does it while you tend your flocks by night [:0]

its the drugs,y-know.
Title: Re: Question of the Week - Old Version
Post by: DoctorBeaver on 01/03/2006 16:36:07
That's silly
Title: Re: Question of the Week - Old Version
Post by: ukmicky on 02/03/2006 00:39:53
quote:
originally by ukmicky
 At the bottom of the arc i would have thought

 
quote:
The simple answer is at bottom dead centre.


Chris

HMMM its not often i get things right but occasionally i astound myself and others and produce the goods.

Where's my congratulations, where's my prize. i want my goody bag [:D]

Michael
Title: Re: Question of the Week - Old Version
Post by: clouded.perception on 08/03/2006 06:59:13
Charmeleons have different coloured cells in their skin. To change colour, they 'open up' the cells with the correct pigment, thus showing that colour (or combination of colours) on their skin.

I can picture in my mind a world without hate, a world without war.
And I can picture us attacking that world, because they'd never expect it.
Title: Re: Question of the Week - Old Version
Post by: chris on 08/03/2006 08:52:28
That's very nice, but this week's question is about HOLOGRAMS!

"I never forget a face, but in your case I'll make an exception"
 - Groucho Marx
Title: Re: Question of the Week - Old Version
Post by: JimBob on 08/03/2006 18:09:40
Split a laser beam, record the interference pattern made when this beam shines on an object from two different directions. (It's doned with smoke and mirrors.) Project the record to make the same interferance pattern and shine coherent light on it. Presto, a 3D Hologram.

Perhaps this was ignored because it is so easy. These thngs have been around since the 50's. (I wasn't around then - I was a Science Attache at the Klingon Embassy in Star Cluster 4289-F.)  

Jim
Title: Re: Question of the Week - Old Version
Post by: ampwelder on 08/03/2006 19:13:27
Hologram come from the greek words "whole" (holo) and writing (gram).
  A lazer is used to photograph an object (instead of incoharent-normal- light) it does this in such a way that enough information can be recorded to give the imprestion of a 3-D object. This is an illusion as the holograph is actually only 2-D like a regular picture.
Title: Re: Question of the Week - Old Version
Post by: NakedScientist on 24/03/2006 08:15:51
ANSWER TO LAST WEEK'S QOTW:

"WHAT IS A HOLOGRAM, AND HOW ARE THEY MADE?"

Holograms are made using lasers. You need a laser because the light that is produced is "coherent". That is, all of the light waves in the beam are synchronised, and of the same amplitude (size), so they diffract (bend) identically. You can demonstrate this by shining a laser at a prism. Compared with white light, which splits up into its composite wavelengths because each bends by a different amount upon entering the prism, when a laser is fired at a prism just a single band of light is produced.

To make a hologram a laser beam is fired at a beam splitter. This sends part of the light beam, termed the reference beam, to a piece of photographic film. The other part of the light beam, let's call it the image beam, is directed at, and subsequently reflected off, the object which you intend to turn into a hologram. It, too, then shines onto the same piece of photographic film as the reference beam mentioned above.

When the reference beam and the image beam meet at the photographic plate they have travelled different distances and their light waves no longer line-up with each other precisely. As a result they "interfere" with each other with some waves adding together constructively to make brighter patches and other parts of the wave behaving destructively and cancelling each other out to make darker areas. This is called an intereference pattern, and it's what is subsequently recorded onto the photographic film. This is the hologram, the 3D representation of the original object.

TNS

Title: Re: Question of the Week - Old Version
Post by: NakedScientist on 24/03/2006 08:17:17
Ok, here's this week's QOTW:

"HOW DO STINGING NETTLES WORK ?"

TNS
Title: Re: Question of the Week - Old Version
Post by: wim on 12/04/2006 19:31:30
Stinging Nettles ,each of itís leaves are about 10 cm long, roughly heart-shaped and have large teeth around the leaf edge. They also have tiny hollow hairs on the main stem, leaf stems and on veins on both upper and lower sides of the leaves.
When a human brushes by the plant and it touches their skin, the tiny hollow hairs break off and release formic acid, histamine, acetylcholine, serotonin (5-hydroxytryptamine), plus some unknown compounds. These irritate the skin and cause white itchy spots to appear.

grtz
Title: Re: Question of the Week - Old Version
Post by: daveshorts on 12/04/2006 20:06:13
A hologram is a pattern that when light is reflected (or transmitted depending on the hologram) from it, the light reflecting from the parts of the pattern interfere with each other to produce light leaving as if it came from a 3D object.

Doing this by drawing the pattern from the start is immensely difficult ( although a company in Cambridge is developing a projector that works on a similar idea http://www.lightblueoptics.com/ ) however if you shine light reflected from an object and light coming directly from a laser the two light beams will interfere producing a pattern. Luckly this is the pattern you need to make a hologram.

If you used non-coherent light (light where you can't predict whether it is going to be a peak or a trough from one moment to the next) it would produce an interference pattern that was not stable for long enough to take the photo, so you would actually get an averaging of lots of different interference patterns which won't produce a hologram.
Title: Re: Question of the Week - Old Version
Post by: chris on 28/04/2006 11:57:27
Here's this week's QOTW:

"HOW DOES A SOLAR CELL TURN SUNLIGHT INTO ELECTRICITY?"

Have a go, below...

Chris

"I never forget a face, but in your case I'll make an exception"
 - Groucho Marx
Title: Re: Question of the Week - Old Version
Post by: Hadrian on 28/04/2006 12:06:05

The Structure of a Solar Cell
Over 95% of all the solar cells produced worldwide are composed of the semiconductor material, silicon. As the second most common element in the earthís crust, silicon has the advantage of being available in large quantities. Furthermore while the material is been processed, it does not have an effect on the environment. [http://www.solarserver.de/wissen/photovoltaik-e.html] Another reason for the use of silicon for solar cells is that the energy needed to ionize silicon electrons matches well with the energy of photons coming from the sun. If the photons had less energy (if the solar spectrum were more red), there would not be enough energy to free the electrons, and if the photons had more energy (if the solar spectrum were more blue or ultraviolet), then all the energy above what is needed to break the electrons free would be lost as heat. [http://www.astropower.com/how_solar_cells_work.htm]

To produce a solar cell, the semiconductor (silicon) is ďdopedĒ or contaminated. ďDopingĒ is the intended introduction of chemical elements, which can obtain excess positive charge carriers (p-conducting semiconductor layer) or negative charge carriers (n-conducting semiconductor layer) from the semiconductor material. If two differently contaminated semiconductor layers are combined, a p-n-junction results.

At this junction, an interior electric field is built up, which leads to the separation of the charge carriers that are released by light. Through metal contact, an electric charge can be tapped. If the outer circuit is closed, meaning a user is connected, then direct current flows. A transparent anti-reflection film protects the cell and decreases the reflective loss on the cellís surface. [http://www.solarserver.de/wissen/photovoltaik-e.html]
 



What you do speaks so loudly that I cannot hear what you say.
Title: Re: Question of the Week - Old Version
Post by: razorbill on 14/05/2006 23:19:25
I have'nt progressed that far yet...I still get Duckbumps!
Title: Re: Question of the Week - Old Version
Post by: Cut Chemist on 17/05/2006 05:40:49
How fast is warp speed??
Title: Re: Question of the Week - Old Version
Post by: JimBob on 21/05/2006 03:38:22
Only Scotty and Sulu (and Spock) know. It isn't scientific, it is scince fiction, believed to be fasteer than the speed of light.


The mind is like a parachute. It works best when open.  -- A. Einstein
Title: Re: Question of the Week - Old Version
Post by: chris on 16/06/2006 21:56:58
Now here's a question that I think you'll have fun with:

"Why does a mirror reverse things in the horizontal, but not the vertical axis?"

Answers below please...

Chris

"I never forget a face, but in your case I'll make an exception"
 - Groucho Marx
Title: Re: Question of the Week - Old Version
Post by: another_someone on 17/06/2006 02:48:40
quote:
Originally posted by chris
"Why does a mirror reverse things in the horizontal, but not the vertical axis?"

Answers below please...



This is a question that comes up so often that I feel I should have a standard template with which to answer it.

A mirror does not reverse things.  What a mirror shows is a true image.  It is what we compare a mirror image to that is reversed.

You expect a mirror image to look like a person facing you.  The reason why a mirror image does not look like a person facing you is because the person facing you has turned around to face to.  It is the person who is facing you who is reversed.  The person who is facing you is reversed in the horizontal plane because (s)he has revolved around a vertical axis when turning around to face you.  If that person, rather than turning on their heals to face you, turned around by doing a handstand, then they would be reversed in the vertical plane and not in the horizontal plane.



George
Title: Re: Question of the Week - Old Version
Post by: chris on 20/06/2006 09:49:44
But in terms of the physics of the light waves hitting the mirror, what's happening?

Chris

"I never forget a face, but in your case I'll make an exception"
 - Groucho Marx
Title: Re: Question of the Week - Old Version
Post by: ROBERT on 29/06/2006 16:48:57
quote:
Originally posted by chris

But in terms of the physics of the light waves hitting the mirror, what's happening?



I found these sites on this subject:-
http://www.mathpages.com/home/kmath142.htm
http://www.mathpages.com/home/kmath354.htm
http://www.mathpages.com/home/kmath441.htm
Title: Re: Question of the Week - Old Version
Post by: ROBERT on 29/06/2006 16:48:57
quote:
Originally posted by chris

But in terms of the physics of the light waves hitting the mirror, what's happening?



I found these sites on this subject:-
http://www.mathpages.com/home/kmath142.htm
http://www.mathpages.com/home/kmath354.htm
http://www.mathpages.com/home/kmath441.htm
Title: Re: Question of the Week - Old Version
Post by: rochelle on 10/07/2006 15:49:04
I have a question for you scientists! Lets see if you can answer this one. Tell me why.......tell me why I've never gotten goose bumps? I do get cold, and I do get the shivers, but goose bumps have never followed after experiencing those feelings.
 Hopefully someone will have an answer!
My bf's answer is that I have no soul, but thats obviously not a logical answer.

Rochelle Eloranta
Title: Re: Question of the Week - Old Version
Post by: Mjhavok on 15/07/2006 05:57:23
Goose bumps are a vestige from the days when humans were covered with hair.

When it's hot and you need to cool down, little muscles at the base of each hair relax. Your hair becomes relaxed. Your sweat glands pump out body heat in sweat. Your blood vessels get big to take more heat to the skin to get rid of it. When it's cold, the arrector muscle pulls the hair up. The duct to the sweat glands gets small to conserve heat. Our blood vessels also get small to save heat.

Hair standing up doesn't make very good insulation - we don't have enough fur for that. Humans don't have very much hair on their bodies anymore. Millions of years ago, humans probably did. And that hair standing on end helped keep people warmer. Those little muscles we have on the end of each hair still work. They still make goose bumps.

Cold is not the only thing that can cause our hair to stand on end. Fear or anger can cause the same reflex. The same is true for other mammals. You'll notice that on a cat or dog. Their fur gets bigger when they're angry or afraid.


Perhaps you have some kind of genetic abnormailty that stops you from getting goosebumps. I have heard of someone who couldn't produce tears before but never the goosebumpless disease.

Sorry
Steven
Title: Re: Question of the Week - Old Version
Post by: Mjhavok on 03/08/2006 05:40:52
"Why does a mirror reverse things in the horizontal, but not the vertical axis?"

I think the entry in wikipedia below explains this quite well.

http://en.wikipedia.org/wiki/Reflection_(physics)

Steven
Title: Re: Question of the Week - Old Version
Post by: narasimeena on 11/09/2006 20:20:34
quote:
Originally posted by NakedScientist

THIS WEEK'S QUESTION : - Have a go - brownie points to the person who gets closest to the correct answer, which we'll post in a week's time.

"WHY IS THE SKY BLUE ?"


This is mainly due an effect called as Tindall Effect a property of collides. "If you shine a beam of light through a solution, the light is not effected and passes through. If you shine the beam through a colloid the small aggregates scatter the light and the material looks cloudy or milky" This causes the sky to apprea blue.
Do I get a brownie for this!


Narasi Ramachandran
Title: Re: Question of the Week - Old Version
Post by: narasimeena on 11/09/2006 20:22:52
"WHY IS THE SKY BLUE ?"

This is mainly due an effect called as Tindall Effect a property of collides. "If you shine a beam of light through a solution, the light is not effected and passes through. If you shine the beam through a colloid the small aggregates scatter the light and the material looks cloudy or milky" This causes the sky to apprea blue.
Do I get a brownie for this!



Narasi Ramachandran
Title: Re: Question of the Week - Old Version
Post by: Mjhavok on 12/09/2006 00:39:55
Yes, this question was answered a while back. :-D
Title: Re: Question of the Week - Old Version
Post by: David_D on 13/09/2006 04:03:33
quote:
Our ancesters had much more hair than we do. In those days, when they became cold they would get goosebumps as a skin response which would raise the hairs on their body. ...


I've heard that humans have as many hairs as a chip, but our hair is much finer.
Title: Re: Question of the Week - Old Version
Post by: lightarrow on 13/09/2006 20:23:44
Why it's dark in the night?
(It was a serious question).
Title: Re: Question of the Week - Old Version
Post by: Mjhavok on 11/10/2006 01:08:54
Hairy chips yuk. I prefer mine with salt and vinegar. lol.
Title: Re: Question of the Week - Old Version
Post by: science_guy on 29/10/2006 08:07:32
Why it's dark in the night?
(It was a serious question).

I was taught that not as many photons reach the planet when the sun is on the other side.  The Earth's "night" side is not completely dark, because the light from the sun bounces off the moon and light shines from faraway stars.  More recently, though, light pollution from the lights in citys have made it harder to see stars.  The night sky is never completely dark.

That answer your question?
Title: Re: Question of the Week - Old Version
Post by: lightarrow on 29/10/2006 09:55:08
No.
The question is very simple: why in the night there is not as such ligh as in the daylight? (Or almost, or more?).
I'm not talking about complete dark, just the usual concept of dark we all have.
(The answer is not trivial)
.
Title: Re: Question of the Week - Old Version
Post by: lightarrow on 21/11/2006 09:34:21
No one have any idea?
Title: Re: Question of the Week - Old Version
Post by: Heliotrope on 28/11/2006 19:26:45
First of all define night. Then define dark.
Your answer will follow logically.

If not, I'll have a go at it when you have some definitions.
Title: Re: Question of the Week - Old Version
Post by: lightarrow on 29/11/2006 22:53:03
First of all define night. Then define dark.
Your answer will follow logically.
If not, I'll have a go at it when you have some definitions.


Night = the sun is behind the earth.
Dark = There is not enough light to play tennis or to read a book or to make precision work...
Title: Re: Question of the Week - Old Version
Post by: ukmicky on 29/11/2006 23:31:31
Its dark at night for us humans because we have evolved to do most of our survival work (hunting and gathering) during daylight conditions. And therefore we have not been equipt with enough light collecting cells in our eyes or specialist systems like cats have for us us to see well in low light conditions.
Title: Re: Question of the Week - Old Version
Post by: lightarrow on 30/11/2006 12:35:34
Its dark at night for us humans because we have evolved to do most of our survival work (hunting and gathering) during daylight conditions. And therefore we have not been equipt with enough light collecting cells in our eyes or specialist systems like cats have for us us to see well in low light conditions.
Interesting consideration, Michael.
But my question was different: why it is physically dark in the night? Why there is (almost) no light, or much less light in the night than during the day?
You shoudn't give anything for granted, believe me.
Title: Re: Question of the Week - Old Version
Post by: kalimna on 15/12/2006 18:20:28
And Im guessing that your answer has little to do with the fact  that of all the photons streaming from the sun (primary source of 'light' received by the earth), at night they are only interacting with the side facing the sun? And hence the side away from the sun is receiving only starlight (and reflected sunlight from the moon)....
Or am I missing something here?
Title: Re: Question of the Week - Old Version
Post by: lightarrow on 16/12/2006 13:39:05
And Im guessing that your answer has little to do with the fact  that of all the photons streaming from the sun (primary source of 'light' received by the earth), at night they are only interacting with the side facing the sun? And hence the side away from the sun is receiving only starlight (and reflected sunlight from the moon)....
Or am I missing something here?

You don't miss anything, the answer has nothing to do with that.
Title: Re: Question of the Week - Old Version
Post by: kalimna on 16/12/2006 15:09:49
Hmmm, well in that case, Im stumped! Unless the answer is one of those metaphysical philosophising answers. 'Why is it dark?' - 'Because it is not light'.......
Throw us a bone here :)

Adam
Title: Re: Question of the Week - Old Version
Post by: lightarrow on 17/12/2006 14:44:40
Hmmm, well in that case, Im stumped! Unless the answer is one of those metaphysical philosophising answers. 'Why is it dark?' - 'Because it is not light'.......
Throw us a bone here
:)

Ok. The bonus is:
star's light.
Title: Re: Question of the Week - Old Version
Post by: Soul Surfer on 07/02/2007 10:04:05
Just latched on to this I think he is talking about "Olbers paradox"  If the universe was infinite every line of sight would end up on a star and it would be uniformly bright.  The fact that it is dark at night means that the universe is finite in space time or both.

It is also essential for life to work to have a heat flow so a uniform high temperature universe without light or dark bits would be boring and devoid of life.
Title: Re: Question of the Week - Old Version
Post by: lightarrow on 07/02/2007 12:00:17
A winner! At last! Cheers!

The Wiki explanation, however, is focused more on the universe's expansion, and the consequent Doppler redshift of light from distant stars (frequency and intensity becomes lower and lower with distance).


http://en.wikipedia.org/wiki/Olber%27s_paradox

So, folks, the night is dark Because of the Big Bang!
Title: Re: Question of the Week - Old Version
Post by: jolly on 24/02/2007 19:12:30
i guess its because as your skin gets cold it shrinks, as all things do, and as it shirks it makes little hills with air between them which helps them retain heat when used in conjuction with the bodies hairs, the bodies heat then has to travel up through these little hills as if theres extra skin there. so it could be like the body gives itself an extra two or three layers of skin slowing down heat loss; and keeping you warmer just long enought for you to find a jumper.lol best guess why is it?
Title: Re: Question of the Week - Old Version
Post by: jolly on 24/02/2007 19:13:55
sorry answered without realising it had finished.
Title: Re: Question of the Week - Old Version
Post by: Mjhavok on 04/04/2007 17:00:29
QUESTION: WHAT IS THE SPEED OF GRAVITY?
Title: Re: Question of the Week - Old Version
Post by: lightarrow on 04/04/2007 19:32:34
QUESTION: WHAT IS THE SPEED OF GRAVITY?
C
Title: Re: Question of the Week - Old Version
Post by: Mjhavok on 04/04/2007 19:50:06
Einstein extracted a wave equation from his theory of general relativity that does state that gravity would travel at approximately 186,000 miles a second or "C". To my knowledge though, this hasn't been demonstrated.
Title: Re: Question of the Week - Old Version
Post by: lightarrow on 05/04/2007 08:05:52
Einstein extracted a wave equation from his theory of general relativity that does state that gravity would travel at approximately 186,000 miles a second or "C". To my knowledge though, this hasn't been demonstrated.
Do you mean experimentally? Of course not, since, AFAIK, gravitational waves hasn't been even detected yet.
Title: Re: Question of the Week - Old Version
Post by: Mjhavok on 05/04/2007 12:28:11
Yes I meant experimentally.
Title: Re: Question of the Week - Old Version
Post by: lyner on 15/04/2007 16:58:17
As a measurement exercise, it is a nightmare. There is so much 'gravitational interference' from every other mass in the universe. The waves are expected to be very small and v e r y  l o w  f r e q u e n c y. If they were easy to spot, we would have seen them already.
If you could get near a large binary star system, orbiting around its centre  of mass,  or a couple of black holes interfering with each other, - better, still , a  supernova in our back yard, you would be in a better position to detect these waves (if, of course, they exist).
The LIGO   (Laser Interferometer Gravitational-Wave Observatory) is hoping to detect gravitational waves by tiny amounts of movement between mirrors situated on the Earth and spaced by a few km.  LISA (Laser interferometer space antenna) is planned in the fairly near future, which will detect the relative wobbling of a set of satellites  - spaced by a few million km - as gravitational waves go past.
Nothing to report yet but keep your fingers crossed and avoid slamming doors and general loud behaviour; that realy doesn't help the sensitive equipment.
Title: Re: Question of the Week - Old Version
Post by: lightarrow on 16/04/2007 12:24:27
[...]
Nothing to report yet but keep your fingers crossed and avoid slamming doors and general loud behaviour; that realy doesn't help the sensitive equipment.
Yes. I have never been able to understand how they can remove the error due to all the tiny earthquakes there are constantly in our planet.
Title: Re: Question of the Week - Old Version
Post by: lyner on 18/04/2007 09:39:21
There would be some directivity in the sensitivity of the measuring array, presumably. You could avoid Interference from Earth by looking 'tangentially', perhaps, and then pick your moments for measurement when you are not pointing at anything too close and 'noisy'.
That's the technique for radio astronomy, after all, when your telescope is not steerable.
I would like to know the effective 'beamwidth' of the detector; it could be pretty narrow in the case of the LISA system, because of the enormous aperture. LIGO is not that big, however. Just a lot less sensitive, I would guess.
Title: Re: Question of the Week - Old Version
Post by: jolly on 28/04/2007 01:51:30
Sorry thats a silly question.
Gravity does not have a speed.
What are you really asking? Earth gravity I suppose your talking about. It depends on the mass, different masses are affected differently.
The speed of an object affected by earths gravity?
Gravity itself doesnt have a speed its a force- Not like light which is radiation and has a speed of sorts.
The question makes no sense.
I mean black holes are the strongest gravity zones so are you asking a what speed are you pulled into them? because that again depends on the blackholes size.
Are you asking at what speed you travel around blackholes- our sun travels about 42,000 miles an hour around our milky ways super massive black hole.
But your question is about gravities speed and really it does not have a speed- In my opinion!
Title: Re: Question of the Week - Old Version
Post by: Mjhavok on 28/04/2007 01:57:28
If the sun disapeared we wouldn't instantly verge off out of orbit. This means gravity isn't instant. Saying "Sorry thats a silly question" isn't helping the discussion.
Title: Re: Question of the Week - Old Version
Post by: jolly on 28/04/2007 12:14:55
If the sun disapeared we wouldn't instantly verge off out of orbit. This means gravity isn't instant. Saying "Sorry thats a silly question" isn't helping the discussion.

How is that exactly- there would be no orbit if the sun disapeared- and you would verge off- actually. Gravity is a constent and therefore always affects things with in it arena- instantly. So what are you asking? If the sun disapeared how quickly will we be influenced by another star? answer is straight away.
Title: Re: Question of the Week - Old Version
Post by: Mjhavok on 28/04/2007 14:02:04
If the sun disapeared we wouldn't instantly verge off out of orbit. This means gravity isn't instant. Saying "Sorry thats a silly question" isn't helping the discussion.

How is that exactly- there would be no orbit if the sun disapeared- and you would verge off- actually. Gravity is a constent and therefore always affects things with in it arena- instantly. So what are you asking? If the sun disapeared how quickly will we be influenced by another star? answer is straight away.

Sorry what I mean to say was "If the sun disapeared we wouldn't instantly verge off out of orbit instanly". It would verge off but not instantly." If you disagree with that you are wrong.
Title: Re: Question of the Week - Old Version
Post by: jolly on 28/04/2007 16:04:01
Hello, if the sun disappeared there would be nothing to orbit.
We would stop and go somewhere else- straight away. All the planets would fly off in the same direction. As the gravity from either the super massive blackhole at the milky ways core or a closer star would pull us in.
What are you getting at that our speed and direction would remain the same for a while after the sun disappeared- that is totally un-true. The secound the sun disappeared the earth and other planets would pull towards the next high gravity source.
So what you planning- Gonna destroy the sun as part of some stupid experiment, to see if your ideas are correct- Thats inteligent.

Even if you did fly off in the same dirrection for a while the gravity from near by stars would have an affect on you and slow you down.
Gravity has no speed- It is intentanious- As its always there.
Title: Re: Question of the Week - Old Version
Post by: Mjhavok on 28/04/2007 16:19:49
I disagree.
Title: Re: Question of the Week - Old Version
Post by: i am bored on 28/04/2007 18:19:15
QUESTION: WHAT IS THE SPEED OF GRAVITY?
  9.8 m/s^2
Title: Re: Question of the Week - Old Version
Post by: lightarrow on 28/04/2007 19:43:56
Hello, if the sun disappeared there would be nothing to orbit.
Yes, but when? If the sun moved, clearly orbits should vary as well. Let's say that the sun suddenly moves at 00:00. When will the planets feel this variation? Not immediately, because that "information" cannot travel faster than light's speed. According to Einstein's general relativity, it travels exactly at light's speed, indeed.
Title: Re: Question of the Week - Old Version
Post by: jolly on 29/04/2007 11:57:09
Yes, but when? If the sun moved, clearly orbits should vary as well.

The sun is always moving around the milkly way at about 42,000 mph. and the orbits are affected to a degree.

Let's say that the sun suddenly moves at 00:00.
So what are you saying 'lets say the sun just stopped moving'- Not gonna happen thats impossible.

When will the planets feel this variation? Not immediately, because that "information" cannot travel faster than light's speed. According to Einstein's general relativity, it travels exactly at light's speed, indeed.
Right the affects of the super massive black hole at the center of the milkly way are felt throughtout our galaxcy- and beyond, as the next closest galaxcy is currently pulling towards us.
Gravity is a constent- in other words it is just there- immediate- It may when first forming have taken a while to spread out to where it is now- but as it is now, it is just there.
We are all caught with-in gravity; and the affect of gravity- will be instentaniuos as a result. Gravity is nothing like light. Once in position- its there- and as a result you will feel the affects straight away.
Kinda like a spiders web.
Light is radiation- Gravity is a force, Gravity once it has formed this spiders web- ergo, the area of its influence. will affect the things with-in its grasp straight away- and under those circumstances it has no speed it will be felt straight away.


:-Because that "information" cannot travel faster than light

Since when is matter- information.
Title: Re: Question of the Week - Old Version
Post by: rosy on 29/04/2007 12:29:01
Nic- the "speed of gravity" being discussed here is the speed at which the effect of gravity propagates through space. It has been suggested (derived from the maths) that this occurs at the speed of light (3x108 ms-1), but this hasn't been experimentally demonstrated (even assuming it's true this would be unsurprising since the experiments are a total nightmare due to the amount of competition from noise).
9.8 ms-2 is the rate of acceleration due to gravity at the earth's surface, but the magnitude of that is due to the mass of the earth. On the moon it's about 1/6 of that value.
Title: Re: Question of the Week - Old Version
Post by: another_someone on 29/04/2007 15:43:06
Gravity is a constent- in other words it is just there- immediate-

Constant and immediate are not the same thing (a DC current in a wire is constant, but it still has a speed through the wire).

It may when first forming have taken a while to spread out to where it is now- but as it is now, it is just there.

But if you accept that it took a while to spread out, then it must follow that its absence will also take a while to spread out, otherwise you have an inconsistency in your physics (if the effects of the Sun's gravity were to take 8 minutes to reach the Earth when it was first formed, but instantly disappears when the Sun disappears, then the Earth will have experienced the gravity of the Sun for 8 minutes less than the Sun was actually producing gravity - thus if there is a time lag in the effect of an increase of gravity, then there should be a similar time lag in it diminishing).

Light is radiation- Gravity is a force

The difference is not as much as you indicate.

Light is merely a manifestation of the coulomb force (i.e. the force of an electric field).  We perceive light as a wave because of the finite speed at which the coulomb force travels, and the effects of General Relativity upon the coulomb force emanating from a moving electrically charged particle (as one would have from the electrons moving in a piece of wire under the effect of an electric voltage applied to the wire).

:-Because that "information" cannot travel faster than light

Since when is matter- information.

Gravity does carry information, just as an electric field carries information.

If you are sitting on a beach, with no view of the sky, you may nonetheless observe the ebb and flow of the tide, and from that deduce information about the position of the moon.  In that case, the information is not very precise, but it is information, and it is information that is solely transmitted by the gravitational pull of the moon upon the oceans.  Thus, if gravity was instantaneous, then this information would be received by us instantaneously.
Title: Re: Question of the Week - Old Version
Post by: Mjhavok on 29/04/2007 16:15:15
It makes me happy when George answers.
Title: Re: Question of the Week - Old Version
Post by: jolly on 29/04/2007 22:02:43
Gravity is a constent- in other words it is just there- immediate-

Constant and immediate are not the same thing (a DC current in a wire is constant, but it still has a speed through the wire).

That is only true while the electric applience is being used.

Gravity is a constent- in other words it is just there- immediate-
It may when first forming have taken a while to spread out to where it is now- but as it is now, it is just there.

But if you accept that it took a while to spread out, then it must follow that its absence will also take a while to spread out, otherwise you have an inconsistency in your physics

Right yes, it may take a while to reach its full area of influence- but how are you going to find out what that speed is; because you are currently trapped with-in that area of influence- that is not just our sun but also the other stars and the supermassive black hole at our galaxys core. Even if you remove the sun- the others still affect you instantly. In other words it really does not matter how long it took to create it full area of influence- As once formed it will affect everything with-in its area of influence instentaiously.

Gravity is a constent- in other words it is just there- immediate-

Constant and immediate are not the same thing (a DC current in a wire is constant, but it still has a speed through the wire).

It may when first forming have taken a while to spread out to where it is now- but as it is now, it is just there.

If you are sitting on a beach, with no view of the sky, you may nonetheless observe the ebb and flow of the tide, and from that deduce information about the position of the moon.  In that case, the information is not very precise, but it is information, and it is information that is solely transmitted by the gravitational pull of the moon upon the oceans.  Thus, if gravity was instantaneous, then this information would be received by us instantaneously.

O.k you cannot do that the information you talk about is really an effect you see happening as a result of gravities affect on something- But you percieve that; it may be that you think something has been caused by gravity when it has not or that the affect was so small you did'nt notice. Whatever you look at will be affected by all the different gravity sourses around it, which will make the thing you look at, act differently- so until you can identify all of the different gravity sourses and how they affect something inseperation- how can you know.

The trouble here is at the moment you cant- As all the different gravity influences are jumbbled up togther and we do not have the understanding or technology to see them in isolation- any assertion will simply be a best guess.
   
Just because you do not notice an affect does not mean you are not being affected-
e.g the plane thats lost it engine and is flying free- the passengers may not notice that they are glyding.
"honey, the ground is getting very close all a sudden" "stop worrying dear the pilot knows what he's doing" BANG

So as I said before we are under gravities influence and in that situation, its affect will be instentanious- ergo gravity has no speed.

on the creation of a new black hole you could look to see how quickly the things around it are affected- but you would need to add into that equation what other gravities are affecting those things near it as they may speed up or slow the black holes visual affects. 
Title: Re: Question of the Week - Old Version
Post by: another_someone on 30/04/2007 03:17:44
Constant and immediate are not the same thing (a DC current in a wire is constant, but it still has a speed through the wire).

That is only true while the electric applience is being used.

Nothing to do with appliances - if I connect a wire from the positive terminal of a battery to the negative terminal of the same battery, a DC current will flow along that wire.

Gravity is a constent- in other words it is just there- immediate-
It may when first forming have taken a while to spread out to where it is now- but as it is now, it is just there.

But if you accept that it took a while to spread out, then it must follow that its absence will also take a while to spread out, otherwise you have an inconsistency in your physics

Right yes, it may take a while to reach its full area of influence- but how are you going to find out what that speed is; because you are currently trapped with-in that area of influence-

You don't need to observe its impact upon you (in any event, one cannot judge speed by looking at one location - one must observe at least two locations).  Thus, if you observe the impact of changes in gravity upon two or more other bodies that are separated by a distance, you can tell if a change in gravity effects both objects at the same time, or it effects one object before the other.

In other words it really does not matter how long it took to create it full area of influence- As once formed it will affect everything with-in its area of influence instentaiously.

But you have not explained, if there is a delay in gravity reaching you when it is being 'formed', why that same delay should not exist when the gravity is being destroyed?

In your world, one could get the rather perverse situation where you detect the loss of a  gravitational field before you detect the existence of a gravitational field (because the detection of the creation of the gravitational field took a finite time to reach you, but the collapse of the gravitational field arrived instantaneously).

If you are sitting on a beach, with no view of the sky, you may nonetheless observe the ebb and flow of the tide, and from that deduce information about the position of the moon.  In that case, the information is not very precise, but it is information, and it is information that is solely transmitted by the gravitational pull of the moon upon the oceans.  Thus, if gravity was instantaneous, then this information would be received by us instantaneously.

O.k you cannot do that the information you talk about is really an effect you see happening as a result of gravities affect on something- But you percieve that; it may be that you think something has been caused by gravity when it has not or that the affect was so small you did'nt notice. Whatever you look at will be affected by all the different gravity sourses around it, which will make the thing you look at, act differently- so until you can identify all of the different gravity sourses and how they affect something inseperation- how can you know.

The trouble here is at the moment you cant- As all the different gravity influences are jumbbled up togther and we do not have the understanding or technology to see them in isolation- any assertion will simply be a best guess.
   
Just because you do not notice an affect does not mean you are not being affected-
e.g the plane thats lost it engine and is flying free- the passengers may not notice that they are glyding.
"honey, the ground is getting very close all a sudden" "stop worrying dear the pilot knows what he's doing" BANG

So as I said before we are under gravities influence and in that situation, its affect will be instentanious- ergo gravity has no speed.

on the creation of a new black hole you could look to see how quickly the things around it are affected- but you would need to add into that equation what other gravities are affecting those things near it as they may speed up or slow the black holes visual affects. 


If one takes a solipsistic approach, one can never actually prove anything beyond one's own mere existence; but in practical terms, there is overwhelming evidence that the tides are caused predominantly my the pull of the moon upon the Earth.  You are correct that other bodies also have an influence, but the tides are so obviously synchronised to the orbit of the moon, and there is nothing else which is synchronised to the same extent with the ebb and flow of the tides, that I think we can regard it as highly improbable that the dominant force exerted upon the tides emanates from the Moon.
Title: Re: Question of the Week - Old Version
Post by: jolly on 01/05/2007 00:53:36
With regards to your dc battery you have still created a circuit.
 
:why that same delay should not exist when the gravity is being destroyed?:

Why on earth are you thinking about destroying gravity?

The tides are affected by the sun, moon and earths gravity and probably by other things to- just because they follow the moon- really doesnt prove anything as if it was just the moon the tides could be larger or smaller- The other things affect the tides to- but how? does the earths gravity increase or decrease the tide- how does the sun affect it- You do not know is the answer.
Title: Re: Question of the Week - Old Version
Post by: another_someone on 01/05/2007 01:22:37
With regards to your dc battery you have still created a circuit.

Indeed, since you cannot have a current without a circuit (and I started by referring to a current), but I was merely stating that there was no need to include an appliance in the circuit.
 
:why that same delay should not exist when the gravity is being destroyed?:

Why on earth are you thinking about destroying gravity?

It was in response to Steven's comment about what would happen if the Sun disappeared - if the Sun instantaneously absented itself, then its gravity would also absent itself - and this whole discussion is premised on the question how long would it take for the Earth to respond to the loss of gravity brought about by the loss of the Sun.

The tides are affected by the sun, moon and earths gravity and probably by other things to- just because they follow the moon- really doesn't prove anything as if it was just the moon the tides could be larger or smaller- The other things affect the tides to- but how? does the earths gravity increase or decrease the tide- how does the sun affect it- You do not know is the answer.

As I said before - absolute proof on anything is an impossibility - one cannot even provide absolute proof that the Earth and the Sun even exist.

On the other hand, the correlation of the tides with the Moon's orbits, and that the tides are highly predictable (even the effect of the Sun and nearby planets can be calculated), that the degree of certainty in the model we have of the tides is very high indeed.

So, the answer is that we do believe we know the effect the Sun, the Earth, and the Moon has on the tides - it is not that difficult a calculation to make with modern computers.
Title: Re: Question of the Week - Old Version
Post by: jolly on 02/05/2007 13:18:32
1, gravity and electricity are different So why are you using an analogy about electricity to explain gravity.

"the question how long would it take for the Earth to respond to the loss of gravity brought about by the loss of the Sun."

As I said striaght away as even residual effects would not be anything compared to the others.


"So, the answer is that we do believe we know the effect the Sun, the Earth, and the Moon has on the tides - it is not that difficult a calculation to make with modern computers."

Well yeah 'believe' not know. Best assumption. As I said before- how- does the earths gravity increase or decrease the tide?- how does the sun affect it?- You do not know is the answer. you assume the answer, but dont actually know.




Title: Re: Question of the Week - Old Version
Post by: Batroost on 05/05/2007 11:41:47
Quote
how- does the earths gravity increase or decrease the tide?-

The tide arises because the Earth isn't flat. No hang-on that sounds stupid... What I mean is that because the Earth isn't flat it is spread out at a range of distances from both the Sun and the Moon. For example, the side of the Earth that is in daylight is (a bit) closer to the Sun than the side that is in darkness. The same applies to the sides facing and away from the Moon - much smaller than the sun but also 400 x closer.

It is this difference in gravitational pull from front-to-back that gives an imbalance in gravitation. It's a small difference (about 1/10,000,000th of the Earth's gravity) but acting on a large mobile body of water the effect is clearly measureable as a small 'bulge'. Throw in the Earth's spin and the Moon's orbit around the Earth and everything works. What complicates tide prediction is teh funnelling effects of landmasses i.e. tide heights close to land, in inlets and channels are much more varied than in open ocean.

If you want to see the maths (and it's not hard to follow) have a look at the link from:

http://www.clupeid.demon.co.uk/tides/simple.html (http://www.clupeid.demon.co.uk/tides/simple.html)

Best wishes,

Batroost
Title: Re: Question of the Week - Old Version
Post by: jolly on 06/05/2007 21:13:03
Quote
how- does the earths gravity increase or decrease the tide?-

The tide arises because the Earth isn't flat. No hang-on that sounds stupid... What I mean is that because the Earth isn't flat it is spread out at a range of distances from both the Sun and the Moon. For example, the side of the Earth that is in daylight is (a bit) closer to the Sun than the side that is in darkness. The same applies to the sides facing and away from the Moon - much smaller than the sun but also 400 x closer.

Well thats not gravity thats the shape of the earth your talking about!

It is this difference in gravitational pull from front-to-back that gives an imbalance in gravitation. It's a small difference (about 1/10,000,000th of the Earth's gravity) but acting on a large mobile body of water the effect is clearly measureable as a small 'bulge'. Throw in the Earth's spin and the Moon's orbit around the Earth and everything works. What complicates tide prediction is teh funnelling effects of landmasses i.e. tide heights close to land, in inlets and channels are much more varied than in open ocean.

If you want to see the maths (and it's not hard to follow) have a look at the link from:

http://www.clupeid.demon.co.uk/tides/simple.html (http://www.clupeid.demon.co.uk/tides/simple.html)

Best wishes,

Batroost

So you measure the earth gravity as a small buldge how do you know thats the earths gravity effect, I certainly wouldnt think that the earths gravity would cause a buldge- If anythink it would resitict the tides flow and size!

by the way love the link:

"The Sun also has quite a large effect, but for all practical purposes we can ignore the effects of all the other heavenly bodies".

And on the moon:

"The answer is that it's also moving sideways. As it travels sideways, which would take it away from the Earth, it also falls downwards, and the net movement keeps it at (approximately) the same distance". (not true I'm afraid its moving away!)

And on the Sun:

"Exactly the same reasoning applies to the effect of the Sun, although in this case the centre of mass is within the Sun, and the centrifugal force on the near side of the Earth is actually downward. It's no coincidence that in both cases the forces balance, because the centrifugal force is proportional to the orbital speed, which in turn is related to the mass and distance of the orbiting bodies".

(Right so if these forces balence each other then there should be no tide- as they would neutralize each other out!  Not the case is it?)

And my fav

"practical influence on the height of the tide is not included in this theory at all" Anyway.lol
Title: Re: Question of the Week - Old Version
Post by: jolly on 07/05/2007 20:11:15
Is'nt it About time we had a new question?
Title: Re: Question of the Week - Old Version
Post by: Mjhavok on 08/05/2007 01:30:46
QUESTION:DOES MIXING ALCOHOLIC DRINKS GET YOU DRUNK FASTER?
Title: Re: Question of the Week - Old Version
Post by: Batroost on 09/05/2007 21:43:31
Quote
Is'nt it About time we had a new question?

A new way for Trolly to say "LAST POST!"....?
Title: Re: Question of the Week - Old Version
Post by: JimBob on 13/05/2007 18:11:42
QUESTION:DOES MIXING ALCOHOLIC DRINKS GET YOU DRUNK FASTER?

From vast experience - NO. It is simple - alcohol (of any nature) in per second = drink in X minutes
Title: Re: Question of the Week - Old Version
Post by: jolly on 13/05/2007 22:34:19
surely it can- if the drinks that are mixed produce more alcohol through a chemical reaction?

And

Quote
Is'nt it About time we had a new question?

A new way for Trolly to say "LAST POST!"....?

Whatīs that bat, sour grapes?
Title: Re: Question of the Week - Old Version
Post by: guest6180 on 14/05/2007 15:26:12
All I know is that...

"Beer before wine makes you feel fine, wine before beer makes you feel queer"

I don't know if there is any scientific reasoning for this but a few unintentional experiments that I have conducted seem to verify it!
Title: Re: Question of the Week - Old Version
Post by: dentstudent on 30/07/2007 15:06:44
If this is the right place for the question of the week, then it's a little out of date! I think there are a few who would like to contribute, but tricky when the question isn't here!
Title: Re: Question of the Week - Old Version
Post by: Karen W. on 01/08/2007 06:13:41
ASK the question Stuart!
Title: Re: Question of the Week - Old Version
Post by: Mjhavok on 01/08/2007 06:47:22
QUESTION OF THE WEEK


Q1: How can birds sit on power lines without getting electrocuted?

Q2: What is the memory capacity of the human brain?

Q3: What is the furthest object visible to the naked eye?

Q4: Why do mints make your breath feel cold?

Q5: What makes Super Glue so strong?

FIVE QUESTIONS. Enjoy!
Title: Re: Question of the Week - Old Version
Post by: Karen W. on 14/08/2007 07:20:56
YAYYYYYY! Thanks Steven! Good questions especially the bird one! Hummmm?
Title: Re: Question of the Week - Old Version
Post by: lightarrow on 14/08/2007 19:01:50
QUESTION OF THE WEEK

Q1: How can birds sit on power lines without getting electrocuted?
Because they switch off the master switch before doing it!
(Someone says it's actually because they only touch one pole of the line, but I think birds are much more intelligent).
Title: Re: Question of the Week - Old Version
Post by: Spanner_Monkey on 19/08/2007 22:02:17
wow I just read through this whole thread and my brain is on overload! you guys really know your stuff!
Title: Re: Question of the Week - Old Version
Post by: Karen W. on 29/08/2007 15:41:20
Alberto, what do you mean by, "one pole of the line,"???

What is the makeup of a birds feet! Are they hollow boned in their feet also or are their feet made from something which would not conduct electricity? Are the lines safe to touch because perhaps they are coated .. Are they only dangerous when they are frayed or broken??? I am really not sure...
Title: Re: Question of the Week - Old Version
Post by: paul.fr on 29/08/2007 15:58:47
Karen,

when a bird sits on a power line, it is only on the one line. You will have noticed that there are two line, should the bird (be rather big and)reach other and touch the other one then it will end up at KFC (or KFB).

The bird is not completing a circuit or touching ground. This is why, when you touch a live wire you will get a shock. You are providing a ground.
Title: Re: Question of the Week - Old Version
Post by: kdlynn on 29/08/2007 16:33:32
and if six geese land on the top wire, break it, and fall on the second one they will also fry. and land in our parking lot at work as we are all trying to figure out why the lights went out
Title: Re: Question of the Week - Old Version
Post by: lightarrow on 29/08/2007 19:30:23
My father worked as policeman (now retired from ~ 30 years) and he told me that once, many years ago, someone made pee from a bridge down to a railway, touching one line with that water. The electricity could so reach the ground, and he died.
Title: Re: Question of the Week - Old Version
Post by: Bored chemist on 29/08/2007 19:56:00
I thoughht they tested that onmythbusters and it didn't really work.
Also, I note with mild amusement that everyone seems to have forgotten question 2 et seq which probably answers it.
Title: Re: Question of the Week - Old Version
Post by: paul.fr on 29/08/2007 20:33:06
I thoughht they tested that onmythbusters and it didn't really work.
Also, I note with mild amusement that everyone seems to have forgotten question 2 et seq which probably answers it.

I never read any of the question, i just saw the post by Karen. I may be having one of my "thicker" than normal days, but having read q2 i don't see how it gives the answer. [???]
Title: Re: Question of the Week - Old Version
Post by: lyner on 05/10/2007 23:33:24
Quote
Q5: What makes Super Glue so strong?
I have never found super glue to be all that strong, actually. The good thing about it is that it goes hard very quickly.
If you want strength, you can't do much better than good old araldite (not the rapid) well mixed and cured at about 60oC.
Title: Re: Question of the Week - Old Version
Post by: Alandriel on 06/10/2007 21:01:00

Q4: Why do mints make your breath feel cold?


Quote
The sensation of coolness is the major effect of menthol when it is applied to the skin or mucosal surface. This is a specific action of menthol on the sensory nerves as menthol alters the movement of calcium. Menthol also acts as an irritant and as a local anaesthetic. The anaesthetic response is probably also caused by mentholís effect on calcium movement in the sensory nerves, but the irritant response is most likely a nonspecific action.

Mentholís effect on calcium transport is probably responsible for the fact that menthol can be used to treat the spasming of the smooth muscle large bowel as observed with irritable bowel syndrome (IBS).

Menthol has a complex sensory effect in the mouth as it influences both taste and temperature receptors as well as smell. Prolonged exposure of the taste receptors to menthol anaesthetised them. While the nerve response after a dose of menthol lasted 2.5 seconds, the tongue receptors remained insensitive to menthol for up to 10 minutes. This was not observed for salt (NaCl) or other solutions.

No - I'm not THAT clever but I found this really good ref:  http://cdavies.wordpress.com/2006/07/06/is-menthol-a-cold-treatment/


What a cool thread!  [;D] literally!!

Must read back more when I have more time on my hands.
Title: Re: Question of the Week - Old Version
Post by: lyner on 01/11/2007 11:14:53
Can anyone tell me about this 'question of the week' thing?
I am sure I miss a lot of good comments and posts in it but it is such a pot-pourri  and un-structured that I can only browse and dip in here and there.  It must be the same for other people.
What is really needed is individual threads with titles - and we have that already- outside Q of the W.
Title: Re: Question of the Week - Old Version
Post by: chris on 03/11/2007 20:25:53
Hi Andrew

this is a vestige of an older initiative we had at the naked scientists. The new QOTW is featured as part of the podcast and the threads are labelled as such and discussed individually - they're in the feedback section. Here's an example:

http://www.thenakedscientists.com/forum/index.php?topic=11159.0

Maybe we should think about moving those threads to here, although I worry that it might become cluttered...

A board all to itself right at the top of the forum might be the best best - what does everyone think?

Chris
Title: Re: Question of the Week - Old Version
Post by: Alandriel on 03/11/2007 20:44:26
It wouln't become cluttered / inaccessible if you index reference the threads.  [:)]
E.g. have a 'master' thread somewhere as a sticky on top of the forum that then indexes all the other threads you want indexed. That way, people could just browse the 'master' thread and then find the individual threads by clicking on their crossreferenced links.

Quite a bit of work, I know - but do-able and very user friendly in the end  [:)]
[hope I'm making sense here]
Title: Re: Question of the Week - Old Version
Post by: paul.fr on 03/11/2007 20:53:20
A separate board is a fine idea, so is that of alandriel's, i do think the QOTW needs its own identity, that way there just may be more in the way of participation.
Title: Re: Question of the Week - Old Version
Post by: BenVitale on 03/11/2007 21:51:50
Could you create a forum for mathematics?
Title: Re: Question of the Week - Old Version
Post by: lyner on 03/11/2007 23:40:18
Hi Chris
For someone who is looking all the time there is no problem - finding what you want is a problem, if you only look now and then. 
Perhaps it would be better to put all posts in the relevant forum and have a copy / link to them in qotw. That way, people could either browse qotw  or find the discussion on their favorite forum, depending on the way their mind works.
Title: Re: Question of the Week - Old Version
Post by: kdlynn on 05/11/2007 03:44:28
chris that sounds like a good idea
Title: Re: Question of the Week - Old Version
Post by: lyner on 09/11/2007 21:51:58
Perhaps the board should be, literally, just this week's posts. It would die after a week or be moved to an appropriate forum by our dedicated moderators
Title: Re: Question of the Week - Old Version
Post by: paul.fr on 21/11/2007 15:17:33
I did just notice this:
http://www.thenakedscientists.com/HTML/content/qotw/

How long has that been there, dave?