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Author Topic: Question of the Week - Old Version  (Read 179233 times)

Offline jai

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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).
 

Offline jai

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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.........
 

Offline Furwa

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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

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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.
 

Offline gsmollin

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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.
 

Offline NakedScientist

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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

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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

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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

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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

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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

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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.
 

Offline gsmollin

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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?
 

Offline NakedScientist

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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

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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

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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.
 

Offline NakedScientist

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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

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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 !'
 

Offline NakedScientist

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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

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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

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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 »
 

Offline nilmot

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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
 

Offline nilmot

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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 »
 

Offline NakedScientist

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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

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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

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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 »
 

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Re: Question of the Week - Old Version
« Reply #224 on: 17/11/2004 02:30:59 »

 

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