# Newton’s laws of motion

By Levi Clancy for Student Reader on
updated

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## Newton's First Law: Law of inertia

An object's velocty will not change unless a force acts on the object. Therefore, if not net force acts upon an object then:

• an object at rest will remain at rest

• a moving object will maintan constant velocity.

This natural resistance to change is the inertia. The mass of an object measures its inertia. Mass and weight are not the same, however.

## Newton's Second Law

If Fnet is the net force acting on an object of mass m, then the aceleration (a) follows the equation:

Fnet = ma

• Fnet is the sum of all forces acting on the object.

• If Fnet = 0, then a = 0.

• A force of 1 kgºm/s² is 1 netwon (N).

## Newton's Third Law

If Object 1 exerts a force F1 on Object 2, then Object 2 exerts a force F2 on Object 1. These forces have the same magnitude but act in opposite directions (F1 = -F2) and act on different objects. These two forces form an action-reaction pair. For every action, there is an equal but opposite reaction. However, the effects of these equal-strength forces can be different. For example, imagine a collision between a bus and a pedestrian. Both the bus and the pedestrian experience equal force, but the pedestrian has less mass and so will undergo more acceleration. The bus will undergo very little acceleration.