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Newton’s laws of motion

By Levi Clancy for Student Reader on

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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.