Newton's laws of motion (Sir I. Newton)

Newton's first law of motion

A body remain continues in its state of constant velocity (that may be zero) unless it is acted on by an external force.

Newton's second law of motion

For unbalanced force working on a body, the acceleration generated is proportional to the force impressed; the constant of proportionality refer to the inertial mass of the body.

Newton's third law of motion

In any system where no external forces are exist; every action force is opposed by an equal and opposite reaction force always.