MadSci Network: Other

Re: What are some of the heat insulator materials ?

Date: Sun Feb 15 19:21:44 2004
Posted By: Chris Fellows, Post-doc/Fellow, Chemistry, University of Sydney
Area of science: Other
ID: 1076832130.Ot

There are basically three ways hot food can get cold- by radiation, conduction, and convection.

All objects emit radiation, which for objects at room temperature will be in the infrared range- light of too low an energy to be seen by our eyes. If this can be reflected back on to the object, it will cool less rapidly, which is why emergency blankets used for patients with a low body temperature are shimmery silver things.

An object will also pass a little bit of its energy from its surface to the matter in contact with it, which will pass it to the matter in contact with them, which will pass it to the matter in contact with them, etc., etc. This is called conduction. This takes away energy slowly through a gas (because there are few molecules interacting with the object) fairly rapidly through a liquid (because there are lots of molecules interacting with the object, and they are free to move), and fairly slowly through most solid matter (since it takes a lot of energy to get the atoms in solids moving). Metals transmit heat fairly effectively, however, because electrons can move freely from one atom to another in a metal, just like molecules in a liquid can move around.

If these were the only two ways heat could be lost from an object, I couldn’t write this, because it would be too hot on the surface of earth for water to stay liquid, and I am mostly water. When you heat a gas or a liquid, the heated gas or liquid will generally expand, and hence move away from the thing heating it, over and above the random motions of the molecules. The faster the gas or liquid is replaced, the more rapidly the object will cool. For example, we might blow on soup to cool it.

If you think about these three ways in which food can lose heat, I am sure you will come up with a number of strategies to keep it warm. Then you could go to the mall and see these same strategies in action!

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