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You know how to add the forces on one object into a resultant. Newton's Third Law is about two objects trading forces. You push on a wall with 50 N.
What does the wall do?
Newton's Third Law
State and apply Newton's Third Law: every force has an equal and opposite reaction force acting on a different object, distinguishing action-reaction pairs from balanced forces
What a learner can do afterwards
- States Newton's Third Law correctly, identifying both the action and reaction force and the objects they act on
- Gives at least two real-world examples (e.g. rocket propulsion, swimmer pushing off a wall)
- Distinguishes a Newton's Third Law pair from balanced forces on the same object
- Explains why a gun recoils when fired using Newton's Third Law
1 · Read
Newton's Third Law says that forces come in pairs. When one object pushes or pulls on a second object, the second object pushes or pulls back on the first object with the same amount of force, but in the opposite direction. These are called action and reaction forces, and they always act on two different objects.
Try it together
A swimmer at the starting wall pushes backward against it with her feet. By Newton's Third Law, the wall pushes forward on the swimmer with the same amount of force. That forward push is what sends her gliding through the water.
Try it together
A rocket engine burns fuel and pushes hot gas downward out the back. The gas pushes back on the rocket with equal force, straight upward. That upward push is called thrust, and it's what lifts the rocket off the ground.
Good to know
Don't mix up a Third Law pair with balanced forces. A pair always involves two different objects and matching forces, like your feet and the wall. Balanced forces, like gravity pulling a book down and a table pushing it up, act on the same object and can be different types of force.
Every push or pull has an equal and opposite partner force acting on a different object. That's Newton's Third Law.
2 · Watch
3 · Play
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Where it sits
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Where this leads
Jobs that lean on this skill. Follow one to see everything it is built on.
Then practise
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