# What is a rigid body?

### What is a rigid body?

Definition of a rigid body:

A rigid body is defined as a body on which the distance between two points never changes whatever be the force applied on it.

Or you may say the body which does not deform under the influence of forces is known as a rigid body.

But, in real life, there would be some force under which the body starts to deform. For example, a bridge does not deform under the weight of a single man but it may deform under the load of a truck or ten trucks. However, the deformation is small.

Since, no object is rigid body in real life; we have to introduce another concept that is concept of resistant body so that we would be able to use it in engineering problems.

Definition of resistant body:

A body is said to be a resistant body, if it does not deform for the purpose for which it is made. For example the chair, it does not deform if a person sits on it, but it will break if you put a load of 1000 kg on it. So a resistant body is rigid for the purpose for which it is used.

Throughout the tutorials, when we will talk about rigid body, this means that we are talking about the resistant body.

Wikipedia Article about the Rigid body: http://en.wikipedia.org/wiki/Rigid_body