Question of the Week - Old Version

  • 433 Replies
  • 180214 Views

0 Members and 1 Guest are viewing this topic.

*

Offline tweener

  • Moderator
  • Neilep Level Member
  • *****
  • 1144
    • View Profile
Re: Question of the Week - Old Version
« Reply #150 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.
----
John - The Eternal Pessimist.

*

Offline Boffy Clywd

  • First timers
  • *
  • 2
    • View Profile
Re: Question of the Week - Old Version
« Reply #151 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 !

 

*

Offline Boffy Clywd

  • First timers
  • *
  • 2
    • View Profile
Re: Question of the Week - Old Version
« Reply #152 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]
 

*

Offline NakedScientist

  • Moderator
  • Sr. Member
  • *****
  • 355
    • View Profile
    • http://www.thenakedscientists.com
Re: Question of the Week - Old Version
« Reply #153 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.


*

Offline NakedScientist

  • Moderator
  • Sr. Member
  • *****
  • 355
    • View Profile
    • http://www.thenakedscientists.com
Re: Question of the Week - Old Version
« Reply #154 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

*

Offline tweener

  • Moderator
  • Neilep Level Member
  • *****
  • 1144
    • View Profile
Re: Question of the Week - Old Version
« Reply #155 on: 06/04/2004 22:18:14 »
Yes.

----
John - The Eternal Pessimist.
----
John - The Eternal Pessimist.

*

BlooGoo

  • Guest
Re: Question of the Week - Old Version
« Reply #156 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.

*

Offline tweener

  • Moderator
  • Neilep Level Member
  • *****
  • 1144
    • View Profile
Re: Question of the Week - Old Version
« Reply #157 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.
----
John - The Eternal Pessimist.

*

Offline Rabbit

  • Jr. Member
  • **
  • 18
    • View Profile
    • http://www.kidsandscience.org
Re: Question of the Week - Old Version
« Reply #158 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...
 

*

Offline gsmollin

  • Hero Member
  • *****
  • 749
    • View Profile
Re: Question of the Week - Old Version
« Reply #159 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.
"F = ma, E = mc^2, and you can't push a string."

*

Offline MayoFlyFarmer

  • Hero Member
  • *****
  • 863
    • View Profile
    • http://www.myspace.com/wiguyinmn
Re: Question of the Week - Old Version
« Reply #160 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!!
<font color="maroon"></font id="maroon">How much CAML do you have in your toes? [;)]

*

Offline neilep

  • Withdrawnmist
  • Naked Science Forum GOD!
  • *******
  • 20602
    • View Profile
Re: Question of the Week - Old Version
« Reply #161 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 !'
Men are the same as women, just inside out !

*

Offline NakedScientist

  • Moderator
  • Sr. Member
  • *****
  • 355
    • View Profile
    • http://www.thenakedscientists.com
Re: Question of the Week - Old Version
« Reply #162 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.


*

Offline NakedScientist

  • Moderator
  • Sr. Member
  • *****
  • 355
    • View Profile
    • http://www.thenakedscientists.com
Re: Question of the Week - Old Version
« Reply #163 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

*

Offline tweener

  • Moderator
  • Neilep Level Member
  • *****
  • 1144
    • View Profile
Re: Question of the Week - Old Version
« Reply #164 on: 06/04/2004 22:18:14 »
Yes.

----
John - The Eternal Pessimist.
----
John - The Eternal Pessimist.

*

BlooGoo

  • Guest
Re: Question of the Week - Old Version
« Reply #165 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.

*

Offline tweener

  • Moderator
  • Neilep Level Member
  • *****
  • 1144
    • View Profile
Re: Question of the Week - Old Version
« Reply #166 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.
----
John - The Eternal Pessimist.

*

Offline Rabbit

  • Jr. Member
  • **
  • 18
    • View Profile
    • http://www.kidsandscience.org
Re: Question of the Week - Old Version
« Reply #167 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...
 

*

Offline gsmollin

  • Hero Member
  • *****
  • 749
    • View Profile
Re: Question of the Week - Old Version
« Reply #168 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.
"F = ma, E = mc^2, and you can't push a string."

*

Offline MayoFlyFarmer

  • Hero Member
  • *****
  • 863
    • View Profile
    • http://www.myspace.com/wiguyinmn
Re: Question of the Week - Old Version
« Reply #169 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!!
<font color="maroon"></font id="maroon">How much CAML do you have in your toes? [;)]

*

Offline neilep

  • Withdrawnmist
  • Naked Science Forum GOD!
  • *******
  • 20602
    • View Profile
Re: Question of the Week - Old Version
« Reply #170 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 !'
Men are the same as women, just inside out !

*

Offline nilmot

  • The Riddler
  • Sr. Member
  • ****
  • 369
    • View Profile
Re: Question of the Week - Old Version
« Reply #171 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
Tom

*

Offline neilep

  • Withdrawnmist
  • Naked Science Forum GOD!
  • *******
  • 20602
    • View Profile
Re: Question of the Week - Old Version
« Reply #172 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 !!!

'Men are the same as women...just inside out !'
Men are the same as women, just inside out !

*

Offline gsmollin

  • Hero Member
  • *****
  • 749
    • View Profile
Re: Question of the Week - Old Version
« Reply #173 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.
"F = ma, E = mc^2, and you can't push a string."

*

Offline neilep

  • Withdrawnmist
  • Naked Science Forum GOD!
  • *******
  • 20602
    • View Profile
Re: Question of the Week - Old Version
« Reply #174 on: 20/04/2004 03:29:51 »
Well...seeing as you put it like that !!!.....err..no sweat !!! *gulp*

'Men are the same as women...just inside out !'
Men are the same as women, just inside out !

*

Offline Buster

  • First timers
  • *
  • 1
    • View Profile
Re: Question of the Week - Old Version
« Reply #175 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.
 

*

Offline tweener

  • Moderator
  • Neilep Level Member
  • *****
  • 1144
    • View Profile
Re: Question of the Week - Old Version
« Reply #176 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.
----
John - The Eternal Pessimist.

*

Offline Dan B

  • Jr. Member
  • **
  • 49
    • View Profile
Re: Question of the Week - Old Version
« Reply #177 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?"
 

*

Offline Dan B

  • Jr. Member
  • **
  • 49
    • View Profile
Re: Question of the Week - Old Version
« Reply #178 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]
 

*

Offline neilep

  • Withdrawnmist
  • Naked Science Forum GOD!
  • *******
  • 20602
    • View Profile
Re: Question of the Week - Old Version
« Reply #179 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 !'
Men are the same as women, just inside out !

*

Offline Dan B

  • Jr. Member
  • **
  • 49
    • View Profile
Re: Question of the Week - Old Version
« Reply #180 on: 04/05/2004 14:38:32 »
[xx(] spoil sport [:D]
 

*

Offline neilep

  • Withdrawnmist
  • Naked Science Forum GOD!
  • *******
  • 20602
    • View Profile
Re: Question of the Week - Old Version
« Reply #181 on: 04/05/2004 14:40:16 »
Soz Dan B....forgive ?

'Men are the same as women...just inside out !'
Men are the same as women, just inside out !

*

Offline Dan B

  • Jr. Member
  • **
  • 49
    • View Profile
Re: Question of the Week - Old Version
« Reply #182 on: 04/05/2004 20:39:25 »
[:D] maybe.
 

*

Offline NakedScientist

  • Moderator
  • Sr. Member
  • *****
  • 355
    • View Profile
    • http://www.thenakedscientists.com
Re: Question of the Week - Old Version
« Reply #183 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

*

Offline cuso4

  • Angel Delight
  • Sr. Member
  • ****
  • 422
    • View Profile
Re: Question of the Week - Old Version
« Reply #184 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
Angel

*

Offline neilep

  • Withdrawnmist
  • Naked Science Forum GOD!
  • *******
  • 20602
    • View Profile
Re: Question of the Week - Old Version
« Reply #185 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 !'  
Men are the same as women, just inside out !

*

Offline NakedScientist

  • Moderator
  • Sr. Member
  • *****
  • 355
    • View Profile
    • http://www.thenakedscientists.com
Re: Question of the Week - Old Version
« Reply #186 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

*

Offline Rokitansky

  • Sr. Member
  • ****
  • 108
    • View Profile
Re: Question of the Week - Old Version
« Reply #187 on: 31/05/2004 15:14:04 »
It filters sunrays in a specific part of a spectrum, part of which is hazard to humans  ?
 

*

Offline Trang

  • Jr. Member
  • **
  • 18
    • View Profile
Re: Question of the Week - Old Version
« Reply #188 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
 

*

Offline chris

  • Neilep Level Member
  • ******
  • 5388
  • The Naked Scientist
    • View Profile
    • The Naked Scientists
Re: Question of the Week - Old Version
« Reply #189 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
I never forget a face, but in your case I'll make an exception - Groucho Marx

*

Offline NakedScientist

  • Moderator
  • Sr. Member
  • *****
  • 355
    • View Profile
    • http://www.thenakedscientists.com
Re: Question of the Week - Old Version
« Reply #190 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

*

Offline Donnah

  • Ma-Donnah
  • Neilep Level Member
  • ******
  • 1756
    • View Profile
Re: Question of the Week - Old Version
« Reply #191 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.
"Remember, if you ever need a helping hand, you will find one at the end of each of your arms." - Audrey Hepburn

*

Offline nilmot

  • The Riddler
  • Sr. Member
  • ****
  • 369
    • View Profile
Re: Question of the Week - Old Version
« Reply #192 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
Tom

*

Offline OmnipotentOne

  • Sr. Member
  • ****
  • 146
    • View Profile
Re: Question of the Week - Old Version
« Reply #193 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.
To see a world in a grain of sand.

*

Offline tweener

  • Moderator
  • Neilep Level Member
  • *****
  • 1144
    • View Profile
Re: Question of the Week - Old Version
« Reply #194 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.
----
John - The Eternal Pessimist.

*

Offline neilep

  • Withdrawnmist
  • Naked Science Forum GOD!
  • *******
  • 20602
    • View Profile
Re: Question of the Week - Old Version
« Reply #195 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 !'
Men are the same as women, just inside out !

*

Offline tweener

  • Moderator
  • Neilep Level Member
  • *****
  • 1144
    • View Profile
Re: Question of the Week - Old Version
« Reply #196 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.
----
John - The Eternal Pessimist.

*

Offline neilep

  • Withdrawnmist
  • Naked Science Forum GOD!
  • *******
  • 20602
    • View Profile
Re: Question of the Week - Old Version
« Reply #197 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 !'
Men are the same as women, just inside out !

*

Offline NakedScientist

  • Moderator
  • Sr. Member
  • *****
  • 355
    • View Profile
    • http://www.thenakedscientists.com
Re: Question of the Week - Old Version
« Reply #198 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

*

Offline NakedScientist

  • Moderator
  • Sr. Member
  • *****
  • 355
    • View Profile
    • http://www.thenakedscientists.com
Re: Question of the Week - Old Version
« Reply #199 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