1. Solids are made up of atoms or a group of atoms placed in a definite geometric arrangement.
2. This arrangement is decided by nature so that the resultant force acting on each constituent due to others is zero. This is the equilibrium state of a solid at room temperature.
3. This equilibrium arrangement does not change with time but it can only change when an external stimulus, like compressive force is applied to a solid from all sides.
4. The constituents vibrate about their equilibrium positions even at very low temperature but cannot leave their fixed positions.
5. As a result, the solids possess a definite shape and size.
