What is a rigid body? Give examples.

A rigid body is an idealized object whose size and shape are unaffected by external forces. Particles that make up the rigid body can be moving under the effects of external forces, but the relative positions of the particles are preserved. A rigid body does not deform; therefore, all the particles of it have the same displacement as the body moves. Similarly, when the rigid body rotates, each particle passes through the same angle about the axis of rotation. While perfect rigidity is impossible, materials such as steel or glass can be approximated as rigid under moderate forces. This simplifies the analysis in physics by assuming no structural deformation under typical conditions.