Newton's Third Law

Newton's Third Lawvideo

Newton's Third Law

• Newton's third law of motion describes the effects of the forces involved when two different objects interact with one another

• This is different to Newton's first and second laws, which describe the effects of forces acting on a single object

• Newton's third law of motion states:

Whenever two bodies interact, the forces they exert on each other are equal and opposite 

• The pair of forces exerted by the interacting objects are known as force pairs

• Newton's third law explains the forces that enable someone to walk

  • The foot and the ground are the two objects interacting

  • The foot exerts a push force on the ground

  • The ground exerts a push force on the foot

  • The forces are equal in magnitude and opposite in direction

Example of Newton's Third Law

• Recognising Newton's third law

  • Use the following three rules to help you identify a third law pair:

  1. The two forces in a third law pair act on different objects

  2. The two forces in a third law pair always are equal in size but act in opposite directions

  3. The two forces are always the same type: weight, reaction force, etc.

     • If you are struggling to name the force, just describe it as a push or pull force