Undeniable Fact: A Cold Hard Fact
Tuesday, February 13, 2007
Ever wonder why an empty glass always feels cold to the touch, regardless of the temperature of the room? The ice lobby doesn't want to know that glass always tends towards a temperature slightly cooler than its surroundings.
This is caused by the Mpemba effect, which also causes hot water to freeze more quickly than cold water.
The melting temperature of glass is far higher than humans can achieve. So to compensate, glass-masters have to add compounds like tungsten and mercury which allow the material to melt at the cost of a "heat debt" - a debt which the glass will pay for the rest of its days. If the glass were to ever fully pay this debt (say, four thousand years from now), it would revert to sand.
This is caused by the Mpemba effect, which also causes hot water to freeze more quickly than cold water.
The melting temperature of glass is far higher than humans can achieve. So to compensate, glass-masters have to add compounds like tungsten and mercury which allow the material to melt at the cost of a "heat debt" - a debt which the glass will pay for the rest of its days. If the glass were to ever fully pay this debt (say, four thousand years from now), it would revert to sand.
Labels: glass, heat, ice, Mpemba effect, temperature, water
7 Comments:
Finally, some more nearly-believable facts. This is at least close to possible reality.
No. The glass feels colder than the air around it because it conducts heat more efficiently than air does. It is drawing the heat out of your hand faster, making it feel cold. The same thing happens when you are barefoot in the bathroom. Although the tile floor and the rug are the same temperature, the tile FEELS colder because it is drawing heat away from your feet much more quickly than the rug is.
chico, what the hell are you talking about?
Chico is talking about the UNDENIABLE FACT that heat transfers from hot to cold. Basic physics. If you hold an ice cube in your hand it melts and your hand turns cold. This is from a loss of heat in your hand which causes the ice to melt. If it worked the other way your hand would freeze and the ice would never melt. Again - BASIC physics.
Most people learn that in science class.
Nice one Chico.
Idiots.
This is the reason why responsible manufacturers tell you never to use glass containers in microwave ovens because of the danger of Rapid Catalytic Reversal.
Thermal conduction is only half the answer, the well-documented Mpemba effect is the real process at work. It is especially pronounced in amorphous solids like glass, and non-periodic crystal ("quasicrystal") solids.
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