Newton's laws of motion

Kinetics is concerned with the relation between force and motion. The basis of this science is the laws of motion formulated by Isaac Newton (1642–1727) in his Principia, published in 1687. The essence of these laws is as follows.

1. First law. If the resultant force acting on a particle is zero, the acceleration of the particle will also be zero, i.e. it will continue in its state of rest or of constant velocity in a straight line.

2. Second law. If the resultant force acting on a particle is non-zero, the particle will accelerate in the direction of the force with a magnitude proportional to the magnitude of the force and inversely proportional to the mass of the particle.

3. Third law. To every action there is an equal and opposite reaction. For instance, if particle A collides with particle B, the reaction from B on A will be equal and opposite to the collision force from A on B.

The laws have been stated here with regard to the motion of a particle. This is convenient for the later development of the equations of motion of a body involving rotation as well as translation. However, in many cases the laws apply equally well to the motion of a body as to a particle. Indeed, Newton introduced the laws with regard to bodies rather than particles.

In order to perform calculations using Newton's laws of motion, it is necessary to specify units of measurement.