The unit of force is the **newton (N)** named after Sir Isaac Newton (1642 - 1727). He observed apples falling from a tree and realised that the force produced by a falling apple is equal to its mass times the earth's gravitational pull. He established the analysis and the theory to predict forces and resulting motion.

A **newton** is the force which when applied to a body of mass of 1 kilogram causes an acceleration of 1 metre per second in the direction in which the force is applied.

The earth's gravitational pull is approximately 9.81 m/s^{2} so 1 kg will produce a force of 9.81 N. This figure is often rounded up to 10 N for ease of use.

1 kg mass produces a force of 10N.

100 kg mass produces a force of 1,000 N.

1,000 kg mass produces a force of 10 kN.