describe only the motion of a body as a whole and are valid only for motions relative to a reference frame. The following are brief modern formulations of Newton's three laws of motion:

First law

An object at rest tends to stay in rest and an object in motion tends to stay in motion in a straight line at constant speed unless acted upon by an outside force.

Second law

If one object has more inertia than another, more force is required to give that object the same acceleration as the first.

Third law

To every action (force applied) there is an equal but opposite reaction (equal force applied in the opposite direction).

Another way of stating Newton's third law, an interaction between two objects, is that, if object A exerts a force on object B, object B will exert the same magnitude force on A, but in the opposite direction.