Rigid Body: A rigid body is a system of particles in which interparticle distances do not change and the
body cannot be deformed no matter how large a force is applied to it. Although a solid body
is not a rigid body, it can be so considered for most of the practical applications.

A rigid body can have three types of motion.

1) Translatory motion : In pure translatory motion at any instant of time every particle of the body has the same velocity.

2) Rotatory Motion: In pure Rotatory Motion about a fixed axis , every particle of the body moves in a circle, which lies in a plane perpendicular to the axis and has its centre on the axis.

3) Combination of Translatory Motion and  Rotatory Motion : It is simply a combination of both kind of motions. Its example is rolling motion.