Question of the Week - Old Version

  • 433 Replies
  • 181016 Views

0 Members and 1 Guest are viewing this topic.

*

Offline jai

  • Full Member
  • ***
  • 64
    • View Profile
Re: Question of the Week - Old Version
« Reply #200 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).

yaaaaay!!!!!!!

*

Offline jai

  • Full Member
  • ***
  • 64
    • View Profile
Re: Question of the Week - Old Version
« Reply #201 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.........

yaaaaay!!!!!!!

*

Offline Furwa

  • First timers
  • *
  • 7
    • View Profile
Re: Question of the Week - Old Version
« Reply #202 on: 13/07/2004 01:31:37 »
Its flourescent paint/sticker =D
And so um it glows...Like all other flourscent stuff.
 

*

Offline gsmollin

  • Hero Member
  • *****
  • 749
    • View Profile
Re: Question of the Week - Old Version
« Reply #203 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.
"F = ma, E = mc^2, and you can't push a string."

*

Offline gsmollin

  • Hero Member
  • *****
  • 749
    • View Profile
Re: Question of the Week - Old Version
« Reply #204 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.
"F = ma, E = mc^2, and you can't push a string."

*

Offline NakedScientist

  • Moderator
  • Sr. Member
  • *****
  • 355
    • View Profile
    • http://www.thenakedscientists.com
Re: Question of the Week - Old Version
« Reply #205 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.

*

Offline roberth

  • Sr. Member
  • ****
  • 246
    • View Profile
Re: Question of the Week - Old Version
« Reply #206 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.
 

*

Offline NakedScientist

  • Moderator
  • Sr. Member
  • *****
  • 355
    • View Profile
    • http://www.thenakedscientists.com
Re: Question of the Week - Old Version
« Reply #207 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

*

Offline NakedScientist

  • Moderator
  • Sr. Member
  • *****
  • 355
    • View Profile
    • http://www.thenakedscientists.com
Re: Question of the Week - Old Version
« Reply #208 on: 24/08/2004 11:47:07 »
Here's this week's QOTW :

WHAT IS A SHOOTING STAR ? IS IT REALLY A STAR ?

*

Offline roberth

  • Sr. Member
  • ****
  • 246
    • View Profile
Re: Question of the Week - Old Version
« Reply #209 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.
 

*

Offline OmnipotentOne

  • Sr. Member
  • ****
  • 146
    • View Profile
Re: Question of the Week - Old Version
« Reply #210 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.
To see a world in a grain of sand.

*

Offline gsmollin

  • Hero Member
  • *****
  • 749
    • View Profile
Re: Question of the Week - Old Version
« Reply #211 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?
"F = ma, E = mc^2, and you can't push a string."

*

Offline NakedScientist

  • Moderator
  • Sr. Member
  • *****
  • 355
    • View Profile
    • http://www.thenakedscientists.com
Re: Question of the Week - Old Version
« Reply #212 on: 27/08/2004 09:38:29 »
Better still, why don't you tell us ! [;)]

*

Offline NakedScientist

  • Moderator
  • Sr. Member
  • *****
  • 355
    • View Profile
    • http://www.thenakedscientists.com
Re: Question of the Week - Old Version
« Reply #213 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

*

Offline gsmollin

  • Hero Member
  • *****
  • 749
    • View Profile
Re: Question of the Week - Old Version
« Reply #214 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.
"F = ma, E = mc^2, and you can't push a string."

*

Offline NakedScientist

  • Moderator
  • Sr. Member
  • *****
  • 355
    • View Profile
    • http://www.thenakedscientists.com
Re: Question of the Week - Old Version
« Reply #215 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.

*

Offline neilep

  • Withdrawnmist
  • Naked Science Forum GOD!
  • *******
  • 20602
    • View Profile
Re: Question of the Week - Old Version
« Reply #216 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 !'
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 #217 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
« Last Edit: 15/09/2004 09:03:42 by NakedScientist »

*

Offline NakedScientist

  • Moderator
  • Sr. Member
  • *****
  • 355
    • View Profile
    • http://www.thenakedscientists.com
Re: Question of the Week - Old Version
« Reply #218 on: 16/09/2004 15:45:09 »
HERE IS THIS WEEK'S QOTW :

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

TNS

*

Offline nilmot

  • The Riddler
  • Sr. Member
  • ****
  • 369
    • View Profile
Re: Question of the Week - Old Version
« Reply #219 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
« Last Edit: 24/09/2004 08:46:49 by nilmot »
Tom

*

Offline nilmot

  • The Riddler
  • Sr. Member
  • ****
  • 369
    • View Profile
Re: Question of the Week - Old Version
« Reply #220 on: 20/09/2004 13:09:34 »
Sorry, just found out that it's not sulphur, it's phosphurous

Tom
Tom

*

Offline nilmot

  • The Riddler
  • Sr. Member
  • ****
  • 369
    • View Profile
Re: Question of the Week - Old Version
« Reply #221 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
« Last Edit: 24/09/2004 08:44:17 by nilmot »
Tom

*

Offline NakedScientist

  • Moderator
  • Sr. Member
  • *****
  • 355
    • View Profile
    • http://www.thenakedscientists.com
Re: Question of the Week - Old Version
« Reply #222 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 !
« Last Edit: 15/11/2004 09:47:54 by NakedScientist »

*

Offline NakedScientist

  • Moderator
  • Sr. Member
  • *****
  • 355
    • View Profile
    • http://www.thenakedscientists.com
Re: Question of the Week - Old Version
« Reply #223 on: 15/11/2004 09:49:32 »
HERE'S THE NEW QOTW :

WHY DO PLANETS SPIN, INCLUDING ORBITING THE SUN ?

*

Offline gsmollin

  • Hero Member
  • *****
  • 749
    • View Profile
Re: Question of the Week - Old Version
« Reply #224 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?"
« Last Edit: 22/11/2004 16:15:46 by gsmollin »
"F = ma, E = mc^2, and you can't push a string."

*

Offline NakedScientist

  • Moderator
  • Sr. Member
  • *****
  • 355
    • View Profile
    • http://www.thenakedscientists.com
Re: Question of the Week - Old Version
« Reply #225 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
« Last Edit: 23/11/2004 10:27:39 by NakedScientist »

*

Offline neilep

  • Withdrawnmist
  • Naked Science Forum GOD!
  • *******
  • 20602
    • View Profile
Re: Question of the Week - Old Version
« Reply #226 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 !'
Men are the same as women, just inside out !

*

Offline DrN

  • Hero Member
  • *****
  • 815
    • View Profile
Re: Question of the Week - Old Version
« Reply #227 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.

*

Offline NakedScientist

  • Moderator
  • Sr. Member
  • *****
  • 355
    • View Profile
    • http://www.thenakedscientists.com
Re: Question of the Week - Old Version
« Reply #228 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 :



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
« Last Edit: 29/11/2004 10:52:18 by NakedScientist »

*

Offline NakedScientist

  • Moderator
  • Sr. Member
  • *****
  • 355
    • View Profile
    • http://www.thenakedscientists.com
Re: Question of the Week - Old Version
« Reply #229 on: 29/11/2004 10:51:26 »
HERE'S THIS WEEK'S QOTW

"HOW DOES WINDSCREEN DE-ICER SPRAY WORK ?"

TNS

*

Offline DrPhil

  • Full Member
  • ***
  • 91
    • View Profile
Re: Question of the Week - Old Version
« Reply #230 on: 29/11/2004 12:01:21 »
I have tried several different brands and found that they don't work very well. :)
 

*

Offline chris

  • Neilep Level Member
  • ******
  • 5424
  • The Naked Scientist
    • View Profile
    • The Naked Scientists
Re: Question of the Week - Old Version
« Reply #231 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
I never forget a face, but in your case I'll make an exception - Groucho Marx

*

Offline chris

  • Neilep Level Member
  • ******
  • 5424
  • The Naked Scientist
    • View Profile
    • The Naked Scientists
Re: Question of the Week - Old Version
« Reply #232 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
I never forget a face, but in your case I'll make an exception - Groucho Marx

*

Offline DrPhil

  • Full Member
  • ***
  • 91
    • View Profile
Re: Question of the Week - Old Version
« Reply #233 on: 29/11/2004 15:22:13 »
Works well in theory but not in practice.
 

*

Offline DrN

  • Hero Member
  • *****
  • 815
    • View Profile
Re: Question of the Week - Old Version
« Reply #234 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.

*

Offline DrPhil

  • Full Member
  • ***
  • 91
    • View Profile
Re: Question of the Week - Old Version
« Reply #235 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.
 

*

Offline DrN

  • Hero Member
  • *****
  • 815
    • View Profile
Re: Question of the Week - Old Version
« Reply #236 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.

*

Offline DrPhil

  • Full Member
  • ***
  • 91
    • View Profile
Re: Question of the Week - Old Version
« Reply #237 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 “-OH” (hydroxyl) groups that can break up the hydrogen bond in water. I suppose that this could break apart the ice crystals.
« Last Edit: 01/12/2004 13:05:46 by DrPhil »
 

*

Offline NakedScientist

  • Moderator
  • Sr. Member
  • *****
  • 355
    • View Profile
    • http://www.thenakedscientists.com
Re: Question of the Week - Old Version
« Reply #238 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

*

Offline NakedScientist

  • Moderator
  • Sr. Member
  • *****
  • 355
    • View Profile
    • http://www.thenakedscientists.com
Re: Question of the Week - Old Version
« Reply #239 on: 07/12/2004 11:30:13 »
Here's this week's QOTW

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

TNS

*

Offline neilep

  • Withdrawnmist
  • Naked Science Forum GOD!
  • *******
  • 20602
    • View Profile
Re: Question of the Week - Old Version
« Reply #240 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 !'
Men are the same as women, just inside out !

*

Offline DrPhil

  • Full Member
  • ***
  • 91
    • View Profile
Re: Question of the Week - Old Version
« Reply #241 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
 

*

Offline NakedScientist

  • Moderator
  • Sr. Member
  • *****
  • 355
    • View Profile
    • http://www.thenakedscientists.com
Re: Question of the Week - Old Version
« Reply #242 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
« Last Edit: 18/12/2004 11:52:37 by NakedScientist »

*

Offline NakedScientist

  • Moderator
  • Sr. Member
  • *****
  • 355
    • View Profile
    • http://www.thenakedscientists.com
Re: Question of the Week - Old Version
« Reply #243 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

*

Offline neilep

  • Withdrawnmist
  • Naked Science Forum GOD!
  • *******
  • 20602
    • View Profile
Re: Question of the Week - Old Version
« Reply #244 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 !'
Men are the same as women, just inside out !

*

Offline gsmollin

  • Hero Member
  • *****
  • 749
    • View Profile
Re: Question of the Week - Old Version
« Reply #245 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...
"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 #246 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 !'
Men are the same as women, just inside out !

*

Offline tups

  • First timers
  • *
  • 2
    • View Profile
Re: Question of the Week - Old Version
« Reply #247 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
 

*

Offline Donnah

  • Ma-Donnah
  • Neilep Level Member
  • ******
  • 1756
    • View Profile
Re: Question of the Week - Old Version
« Reply #248 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
"Remember, if you ever need a helping hand, you will find one at the end of each of your arms." - Audrey Hepburn

*

Offline chris

  • Neilep Level Member
  • ******
  • 5424
  • The Naked Scientist
    • View Profile
    • The Naked Scientists
Re: Question of the Week - Old Version
« Reply #249 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
I never forget a face, but in your case I'll make an exception - Groucho Marx