Matter is any thing that occupies space, possesses mass offers resistance to any stress, example Iron, stone, air, Water. A body of negligible dimension is called a particle. But a particle has mass.
A body consists of a No. of particle, It has definite shape.
A rigid body may be defined as the combination of a large no. of particles, Which occupy fixed position with respect to another, both before and after applying a load.
Or, A rigid body may be defined as a body, which can retain its shape and size even if subjected to some external forces. In actual practice, no body is perfectly rigid. But for the shake of simplicity, we take the bodies as rigid bodies.
An elastic body is that which regain its original shape after removal of the external loads. The basic difference between a rigid body and an elastic body is that the rigid body don't change its shape and size before and after application of a force, while an elastic body may change its shape and size after application of a load, and again regain its shape after removal of the external loads.
