Effects of Heat -

One of the problems in understanding heat is that heat cannot be seen directly. The effects of heat, however, can be seen. One effect of heat is a change in temperature. If heat is added to a beaker of water, the temperature indicated by a thermometer rises. When heat is added to air in a container, two main effects can be seen. One effect is an increase in temperature. The other is an increase in pressure. In these two examples, the effects of adding heat are obvious - changes in temperature and changes in pressure. The addition of heat caused a change in the properties of the substances involved. Another possible effect of adding or removing heat is a change in the state, or phase, of a substance. All substances exist in one of three phases of matter: solid, liquid, or gas. If ice, a solid, is heated, it melts and changes into water, a liquid. So adding heat causes the ice to change its state from a solid to a liquid. If the water is then heated, it boils. The heat causes the water to change its state from a liquid to a gas - steam. The effects of heat are all related to changes in molecular motion. For example, when heat is added, the motion of the molecules that make up a substance increases. When heat is removed, molecular motion decreases.