When body is at rest or it is in uniform motion, no force act on it.

Explanation

Whebn body is at rest or in uniform motion gravitational force act on it.
Forces like friction force viscous force act on body.
When object is at rest in uniform motion on it is zero.
l Consider book at rest on horizontal surface following force act on its.
Here book is at rest hence W=R
Actually it should be like this considering book at rest by Newton first law of motion resultant of external force acting on body must be zero this suggest that normal force and weight should be equal and in opposite direction