Define a rigid body.

Discuss general motion of a rigid body.

________ is a useful mathematical concept to simplify the study of the motion of a rigid body.

Define a ray.

The vector sum of a system of non-collinear forces acting on a rigid body is gives to be non-zero. If the vector sum of all the torques due to the system of forces about a certain point is found to be zero, does this mean that it is necessarily zero about any arbitrary point?

Define centre of mass of a rigid body.