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Home > Physics > Revision videos > Newton's Third Law

Physics

Newton's Third Law

Newton's Third Law

Newton’s Third Law concerns equal and opposite forces. This video shows how this works in two real life situations involving skateboarders, and rockets.

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Key learning points:

  • Newton's Third Law is that "If A exerts a force on B, B exerts an equal but opposite force on A".
  • Forces always occur in "Newton pairs" - an action force and an equal reaction force in the opposite direction.
  • In a rocket, the propellant (e.g. burning gas) is forced backwards (action), so there is forward force on the rocket (reaction).
  • Newton's Second Law is that the acceleration of an object is directly proportional to the unbalanced force and inversely proportional to its mass.
  • Newton's Second Law can be written as F=ma.
  • If the force on an object remains constant but its mass increases, its acceleration will decrease.

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