Solids

Substances exist in three physical forms. The solid, the liquid, and the gaseous. Water, for example, may exist in any one of the about physical forms. If it is ice, it is solid. If it is water, it is a liquid. As water vapor (steam), it is a gas. Three different methods are used to express the physical properties of substances or materials corresponding to the state of the substance.

A solid is any physical substance that retains a certain shape unsupported. It is made of untold billions of molecules, all exactly the same size, weight, and shape that stay in the same relative place to each other and at the same time are in a condition of rapid vibration. The rate of vibration will depend upon the temperature. 

The lower the temperature, the slower the molecules vibrate; the higher the temperature, the faster the molecules vibrate. The molecules are strongly attracted to each other and considerable force is necessary to separate them. A solid must be supported or it will fall vertically. The force supporting a solid is always upward.