NEWTON'S THIRD LAW: ACTION AND REACTION
4 marks · NormalIn a game of tug-of-war, two teams pull on opposite ends of a rope. Both teams seem to pull with all their strength, but neither team is moving.
Explain, using Newton’s third law, why neither team moves even though both are pulling hard.
Describe the action and reaction forces between one team and the rope.
Work this out on paper, then compare with the answer and worked solution below. With a free account you can submit written answers for marking.
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(a) —
(b) —
Common mistakes: Confusing action-reaction with balanced forces on same object
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Marking points
B1 (a) · 1 mark · Explains both teams pull with equal force in opposite directions.
B2 (a) · 1 mark · States Newton’s third law: forces are equal and opposite so teams do not move.
B3 (b) · 1 mark · Identifies one action (team pulls on rope in one direction).
B4 (b) · 1 mark · Identifies reaction (rope pulls the team in the opposite direction with equal force).
Worked solution
(a) Both teams pull with equal force but in opposite directions. According to Newton’s third law, the rope exerts an equal and opposite force on each team, so neither moves if the forces are balanced.
(b) The action is the team pulling the rope. The reaction is the rope pulling back on the team with an equal force in the opposite direction.