Thermal expansion is the change in volume and area of a particular piece of matter in response to changes in temperature.
In general, matter expands when exposed to hot temperatures and contracts when exposed to cold temperatures.
Thermal expansion also has an effect on the density of matter.
When matter is exposed to heat and expands, it then becomes less dense. The reverse is also true when matter is exposed to cold temperatures -- it increases in density.
The manner in which matter expands depends on whether it is a solid, liquid, or gas.
Thermal Expansion Of Solids
Solids expand and contract in direct proportion to temperature change. Area expands twice as much as length, and volume expands three times as much as length.
Materials like graphite and wood expand differently depending upon the direction in which they are expanding.
Thermal Expansion Of Liquids
Liquids, on the other hand, can only expand and contract in volume. One notable exception to thermal expansion, however, is water.
Water expands when it is heated and when it freezes; frozen water is less dense than water in its liquid state.
This is why ice on lakes and in oceans floats, and why lakes and oceans freeze from the top down.
Thermal Expansion Of Gases
Gas behaves less predictably, and it will expand as much as it can depending upon pressure.
Co-Efficient Of Thermal Expansion
The rate at which an object will expand and contract is dependent upon the type of material of which it is composed.
This is referred to as the coefficient of thermal expansion. For example, wood will expand and contract more than metal when exposed to a particular temperature.