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Turn Up the Heat!

Week of March 30, 1998

This morning, like every weekday, I made myself the usual cup of coffee to take to work with me. This time was different, however, in that I wasn't paying as close attention as I should. As the boiling water poured over my hands, I had a few milliseconds to ponder over the difference between temperature and heat. Then I had about an hour to think about it, as I sat watching morning TV (bleah) with a bag of ice over the fingers I had burned.

What we think of as temperature in our daily lives is really a measure of the energy packed into a given amount of material. Every atom (or molecule) of that substance has a certain amount of energy, which is usually reflected as motion, like vibration on an atomic scale. The more the atoms vibrate, the higher we say the temperature is.

But that's different from heat. Heat is a combination of the temperature of an object, plus how efficiently that energy can be transferred to another object. Think of it this way: where I live, it commonly gets as hot as about 40 degrees Celsius. It feels pretty hot, but you can stay out in it for hours without suffering too much. But if you were to get into a bathtub filled with water at that temperature, you'd feel pretty bad after only a few minutes. That's because water is denser than air, and is very efficient at transferring the energy it possesses to your body. If you still don't believe me, try putting your hand in a freezer for a minute, and then try holding an ice cube in your hand for a minute. The air in the freezer is the same temperature as the ice cube, but the ice feels much colder. It can take the heat from your hand much better than air can, so it feels colder.

There are places in the solar system (like the corona of the Sun, for example) where the temperature is millions of degrees. But these places have such a low density that you would feel almost no heat from them! The Universe is under no obligation to conform to our "common sense". We have to make sure our minds are open enough to comprehend its behavior when it does seem to be doing things "incorrectly"!

©2008 Phil Plait. All Rights Reserved.

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