Getting Hotter = Getting Bigger

Now you need to think about states of matter a little bit. We'll start with gases. The idea behind thermal expansion is that gases expand as the temperature increases. If you have a balloon and you heat up the contents, the balloon will get larger. Scientists use the term ideal gas law to describe this activity.

Liquids expand and contract, too, but there is a lot less change than in gases. Scientists say they have a smaller thermal expansion coefficient. As you can probably figure out, solids expand and contract the least of all the states of matter. The expansion coefficient is different for each piece of matter. It is a unique value, just like specific heat capacity. Two examples of coefficients are air at .00367 and alcohol at .000112.

Things Shrink When They get Cold

The opposite of expansion is contraction. If things expand with the addition of heat, it makes sense that they contract when heat is removed. If you remove enough heat from a gas it will become a liquid. Liquids can turn into solids with further cooling. What happens when you remove almost all of the energy from a system? Scientists use the terms absolute zero to describe a system that has no kinetic energy. When there is no kinetic energy in a system, all molecular motion stops. It seems that even the atoms begin to merge at these low temperatures. Physicists have recently created the Bose-Einstein state of matter that has a small group of atoms with nearly all of the kinetic energy taken out of the system.

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