GCSE Physics (AQA)

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Newton's Third Law

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Forces Forces and motion

Newton's Third Law

5:09 Newton's Three Laws
Spec 4.5.6.2.3
Previous Calculating Acceleration Next Inertial Mass
  • Newton's third law: forces exerted by two interacting objects are equal and opposite.
  • It's the last and trickiest of Newton's three laws.
  • Example: pushing a box with a hand results in equal and opposite forces (100 Newtons each).
  • Demonstration with roller skates: two people push each other, moving apart due to equal and opposite forces.
  • Properties of forces obeying Newton's third law:
  • Act on separate bodies.
  • Same type of force.
  • Act along the same line.
  • Opposite directions.
  • Same magnitude.
  • Gravitational force example: Earth and feather experience equal forces, but Earth's movement is negligible due to its mass.
  • Importance for exams: identify when forces obey Newton's third law, even if not obvious.

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