Scott McDonald age 14, of Beaumont, Texas, for his question:

WHY DOES HEAT CAUSE EXPANSION?

Expansion is as increase in the size of a body without the addition of material to the body. Most solids and liquids expand when they are heated and contract when they are cooled. Gases also expand when heated at a constant pressure.

Heat causes expansion because it increases the vibrations of a materials atoms or molecules. The increased vibrations force the atoms or molecules farther apart and the body becomes larger.

Different materials expand by different amounts when their temperature is raised by one degree. For example, aluminum expands twice as much as iron under the same temperature increase.

If a gas is heated in a container that prevents expansion, the pressure of the gas increases.

Heat is actually a form of energy. Heat and energy cannot be seen, but the work they do can. For example, the burning of fuel in the engines of a jet plane creates hot gases. These gases expand and provide the power that moves the plane.