NEWTON'S THIRD LAW: ACTION AND REACTION
2 marks · EasyWhen a rubber ball bounces against a hard wall, explain, using Newton’s third law, why the ball bounces back.
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The ball presses against the wall (action). According to Newton’s third law, the wall pushes back on the ball with an equal and opposite force (reaction), causing the ball to bounce off.
Must show: Explanation that the wall exerts an equal and opposite force on the ball, Relating the reaction force to the change in direction (bouncing back)
Also accept: Wall pushes the ball away with an equal force (Newton’s third law)
Common mistakes: Saying the ball bounces because it is soft (ignores Newton’s third law); Not identifying both the action and the reaction
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Marking points
B1 · 1 mark · States that the wall pushes back on the ball (reaction force)
B2 · 1 mark · States the reaction force is equal in size and opposite in direction, resulting in the ball bouncing back
Worked solution
When the ball hits the wall, it exerts a force on the wall (action). By Newton’s third law, the wall pushes back on the ball with an equal and opposite force (reaction). This force makes the ball move away from the wall, causing it to bounce back.