Some Like It Hotter!

Energy is found in different forms: Sound, light and heat, for instance, as well as potential energy, chemical energy and kinetic energy. Everything that you do or see happening around you involves energy which is being converted from one form to another. This article will focus on heat, which is a form of energy that flows from one point to another because of something we call temperature which is simply a measure of how hot (or cold) something is. The hotter anything is, the more heat energy it has stored. When the same substance is colder, it has a comparatively lower level of energy stored in it.

A "Jewel" of a Discovery

James Joule (1818-1889) was the English scientist who first recognized that heat is a form of energy when he observed an increase in the temperature of water which was being stirred by paddles powered by falling weights. The potential energy in the weights was transferred to the water in the form of heat, raising its temperature. Because of his observations, he was honored by having his name attached to the units of measurement applied to temperature and heat exchange.

All substances are different and require different amounts of heat energy to reach the same temperature. In the case of water, to raise the temperature of 1 kilogram (kg) of pure water 1 degree centigrade, it takes 4200J (joules) of heat energy. "Pure" water means it does not contain other substances, which would change its heat capacity. Oil, for instance, requires less heat energy to reach the same temperature as pure water. In other words, if we add the same amount of heat to both oil and water, the oil will actually get hotter. This difference for each substance is called its thermal or specific heat capacity.

An "Expansive" Idea

Okay, picture this: A bunch of fleas are sitting on a window sill (no, I don't know why they're there). It's kind of shady and then the sunlight starts to filter in through the window, and soon the window sill starts heating up. At first, not much happens, but gradually, a few fleas and then more, and finally all the fleas are jumping up and down like crazy because it's gotten so warm on the window sill. That same thing happens to the molecules that make up most substances as they heat up. And when the molecules start vibrating, they are pushed farther and farther apart, and the substance itself expands. Since liquids and gases have more energy available to them to break free of the force holding them together, they tend to expand more than solids. Not only that, but different solids expand at different rates as well.

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