Want to earn money to help pay for the Volt? A £1,000 question.

[Ron C]

This must be why they do the swim portion of a triathalon first because if the competitors did it second or third, they could go into hypothermia faster and have a lot more trouble since they would be fully heated from running or cycling. Swimmers in the Ironman probably should sit in a barrel of ice-water prior to starting the swim.

A little off topic, but as a spectator of triathalons instead of a participant, I think the whole thing would be a LOT more interesting if swimming were indeed last.

[KyleH]

Just throwing my guess in this mix...

...I suspect it has to do with the polar bonding of the Oxygen of the (H2O) with each other. Oxygen has extra pairs of electrons that allows it have a weak-polar bond with a neighboring H2O molecule. In cooler water, the molecules are more calm and have bonded with each other, while in hotter water, more molecules are more active and less have formed the bond.

When heat is taken out to make ice, water forms in a rigid crystal structure such as ice where it can trap air. Hence, it is obvious that bonds are broken and re formed inorder to make ice.

In the hotter water, the molecules are already separated so many can simply form the bond and fall into place, on the other hand, cooler water needs to break existing bonds and then reform those bonds once they fall into the correct place. The breaking of the bond takes energy, and the release of it gives off the same energy, so it should not take any more cooling to get the same job done, but you need to wait until those bonds have finished breaking, have the molecules move into the correct place, and then setting the new bond. (which takes more time.)

Another factor that may explain it on this similar thinking is that energy is needed to break and set the bonds in order for water to form into ice. A cup of warmer water has more available energy that can be used to break the bonds so those "free-er" molecules can fall into the proper place to set the bonds to make ice; once the new bond is set, energy is release that another molecule to use to break free, settle, create their new bond, release the energy, and repeat.

-KyleH

[KyleH]

I'm not completely convince by your arguments. The following are my explanations on why ice forms on top then outside in...

...Water is rather unique where it's solid form (ice) is less dense than its liquid (water) form. As ice is forming, it forms a crystal structure that can trap any existing air. Then, it simply floats up to the top, touches air, and fill completely with more air and hardens. In some cases, it gets caught light a suction cup along the side.

I think ice cubes form on top because it naturaly floats while it freezes. It only starts to form on the side because it is already touching the top and not float any higher.

...at least, that is my guesses.

Your morbid example is interesting, I would think if another twin (total of triplets) fell in, there is a "right amount" of exercising to have a slow controlled burn of calories that would make him reach hypothermia last--the idea of walking around and working out in a cold environment to stay warm. That is, in a blizzard, would a person standing in one place reach hypothermia faster than his twin walking in a circle around him? That I do not know; maybe an experiment has been done with lab animals?

-KyleH

Also, ever notice that ice usually forms on the surface of a water body? An ice cube will form either on the on the top first or will freeze from the outside in. It's because the interface area between hot and cold looses energy faster. So the surface of the water transfers it's energy to either the air in the freezer or the cold ice cube tray faster. This phenomenon also works on human bodies as morbid as that may sound. If twins fall into frigid sea water, the one that reaches hypothermia faster is the one trashing around the most. I mentioned twins to emphasize all things being equal.

[VikAiRious]

There are more bubbles in cold water that makes it harder to freeze. Makes an insolation effect.

[mikeg3]

There are more bubbles in cold water that makes it harder to freeze. Makes an insolation effect.

I agree.

I first learned of this effect from my mom, who is not a physicist. I tried it myself and she was right.

I asked four PhD physicists and they independently concluded that warmer water has less dissolved gas. Gas acts as an insulator.

[VikAiRious]

I agree.

I first learned of this effect from my mom, who is not a physicist. I tried it myself and she was right.

I asked four PhD physicists and they independently concluded that warmer water has less dissolved gas. Gas acts as an insulator.

You'd think I should be able to spell insulation.

[fishmahn]

Simple - the warm water makes the freezer unit turn on, cooling the water faster.

/humor.

[KyleH]

That doesn't make much sense to me. I am assuming the phenomenon is true if you had the same mass and same volume but at the two different temperatures.

If you had that much "dissolved gases" that would exhibit insulation, then, if you cap both cups of water (one warm/hot, the other cold), wouldn't you be able to see less water in one of them when they get to the same temperature. I think would be easily disproven with a simple 5 min experiment by true professionals / experts. I have not tested it, but I would guess that the answer is more complex than gases.

Does anyone have a point of view from a chemists? I would be more intersted in what chemists say about this as well as the physicists.

-KyleH

I agree.

I first learned of this effect from my mom, who is not a physicist. I tried it myself and she was right.

I asked four PhD physicists and they independently concluded that warmer water has less dissolved gas. Gas acts as an insulator.

[Slapshot28]

Does anyone have a point of view from a chemists? I would be more intersted in what chemists say about this as well as the physicists.

-KyleH

Will a ChE do? Dissolved gas likely will have little or no impact on thermal conductivity (i.e., "insulation"); however, dissolved gas may have a significant impact on the water's freezing point. Here's a detailed reference, from a physicist no less!

http://arxiv.org/pdf/physics/0604224.pdf