Which is not one of Newton's laws of motion?
The total momentum of a system of interacting bodies remains constant, providing no external force acts.
The rate of change of momentum of a body is directly proportional to the external force acting on the body and takes place in the direction of the force.
If body A exerts a force on body B, then body B exerts an equal and oppositely-directed force on body A.
A body continues in a state of rest or of uniform motion in a straight line unless acted upon by some external force.
