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Other forms of Newton's laws

Newton's laws have been written in many ways to make Newton's original book more accessible or easy to understand. Each of the laws can be defined by all of the below definitions. We recommend that you learn the first one of each law, but it is worth reading the others:


Newton's 1st law

  1. A body at rest will remain at rest, and a body in motion will remain in motion unless it is acted upon by an external force.

  2. If the forces on an object are balanced, the object will continue to do what it is already doing.

  3. If the object is stationary it will remain stationary. If the object is moving it will continue to move at the same speed and direction.

  4. Every object persists in its state of rest or uniform motion in a straight line unless it is compelled to change that state by forces imposed on it.

  5. An object at rest will stay at rest, and an object in motion will remain in motion unless acted upon "by an unbalanced force". Also seen as "by an outside force".

  6. Every body continues in its state of being at rest or in uniform velocity unless acted upon by a resultant force.


Newton's 2nd law

  1. The force acting on an object is equal to the mass of that object times its acceleration.

  2. If the resultant force action on an object is not zero, all the forces are said to be unbalanced.

  3. The acceleration of an object is dependant upon two variables – the net force acting upon the object and the mass of the object.

  4. The acceleration produced by a net force on an object is directly proportional to the net force, is in the same direction as the net force, and is inversely proportional to the mass of the object (NOTE: Inversely means "1 over" the mass).


Newton's 3rd law

  1. For every action, there is an equal and opposite reaction.

  2. When an interaction occurs a force cannot exist on its own – there is always a second force acting against it.

  3. If object A exerts a force on object B, then object B exerts an equal but opposite force on object A (these pairs of forces are sometimes called action-reaction pairs).
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