Question

When a number of forces acting simultaneously on a body bring about a change in its state of rest or of uniform motion in a straight line, then these forces acting on the body are said to be

Answer 1

when a number of forces acting on a body bring about a change in its state of rest or uniform motion in a straight line, then these forces acting on the body are said to be unbalanced forces.

Answer 2

Unbalanced forces

When more that one force is acting on a body whether it is on rest or in uniform motion in a straight line, that means these forces are not cancelling each other's effect. And in resultant to these there must be some external force acting on the body in some direction which will make a change in the motion of body. That is why these forces will be called unbalanced forces.