# Newton’s laws of motion

## 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 F_{net} is the net force acting on an object of mass *m*, then the aceleration (*a*) follows the equation:

F_{net} = ma

- F
_{net}is the sum of all forces acting on the object. - If F
_{net}= 0, then a = 0. - A force of 1 kgºm/s² is 1 netwon (N).

## Newton's Third Law

If Object 1 exerts a force F_{1} on Object 2, then Object 2 exerts a force F_{2} on Object 1. These forces have the same magnitude but act in opposite directions (F_{1} = -F_{2}) 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.