Newton's Third Law · seed 1 · A4, ink-friendly. The answer key prints on its own page for grown-ups.
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Newton's Third Law

Science · Forces & Motion · ages 12-13
Name ______________________   Date ____________

  1. When you walk, your foot pushes backward on the floor. What pushes you forward?

    • Your other foot pulls you forward without pushing on the floor
    • Your leg muscles pull the whole body forward without any floor force
    • The floor pushes forward on your foot with equal force

  2. Which pair below is a real Newton's Third Law example?

    • The swimmer pushes the wall, and the wall pushes the swimmer
    • The swimmer pushes the wall, and the water pushes the swimmer
    • The swimmer pushes the wall, and Earth pulls the swimmer down

  3. Your hands push a trolley forward. The floor also pushes up on its wheels. Must the floor's upward force equal your hand force?

    • Yes. All forces acting on a trolley must have equal sizes
    • Yes. The Third Law makes every upward force equal to every forward force
    • No. Those are different interactions

  4. You release a trolley and lift both hands away. What happens to the contact force pair between your hands and the trolley?

    • Both contact forces end when contact ends
    • Both forces last until it stops
    • Only your hands keep pushing after they have lost contact
    • Only the trolley keeps pushing your hands after contact ends

  5. A balloon is moving right while air escapes through an opening pointing right. Which direction does the escaping air push the balloon?

    • Right, alongside the escaping air
    • Left, opposite to the escaping air
    • Neither way, since it is moving

  6. A book sits still on a table. Gravity pulls the book down, and the table pushes the book up. Why is this NOT a Newton's Third Law pair?

    • Both forces act on the book, so they are not a Third Law pair
    • Their directions are opposite
    • They act on different objects, so the table must push harder than Earth pulls

  7. A swimmer pushes the pool wall backward with 60 newtons and glides forward. Which statement about the wall's push on the swimmer must be true?

    • It is less than 60 N because a wall that stays still cannot push as hard
    • It is 60 N in the forward direction
    • It is more than 60 N because moving objects need a stronger reaction

  8. Any two forces that are equal, opposite and act on different objects must be a Newton's Third Law pair.

    Circle one:   True   False

  9. Two ice skaters push off each other. Skater A pushes Skater B with 150 newtons of force. How many newtons does Skater B push back on Skater A?

    Answer: ______________

  10. Sam pushes a fixed wall right with 30 N. He says: "My push must be absent from the wall's force list because the wall stays still." Which correction explains the wall staying still?

    • A fixed wall cannot receive a push
    • Sam's push and the supports' forces can balance on the wall
    • The wall's force on Sam balances Sam's push because both forces act on the wall
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Answer key

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Newton's Third Law W1-mt_fbYbe3YSVj-s1

  1. The floor pushes forward on your foot with equal force · Your foot pushes the floor backward, so the floor pushes your foot forward just as hard. That forward push is what moves you.
  2. The swimmer pushes the wall, and the wall pushes the swimmer · The swimmer pushes the wall, and the wall pushes back on the swimmer just as hard. That's an action-reaction pair.
  3. No. Those are different interactions · The hand-trolley and floor-trolley forces belong to different interactions. Each has its own partner, but the Third Law does not require these two forces to match.
  4. Both contact forces end when contact ends · The hand-trolley contact interaction ends when the hands no longer touch the trolley. Other forces can still act on each object.
  5. Left, opposite to the escaping air · The balloon pushes escaping air right, so that air pushes the balloon left. The thrust direction need not match the balloon's current motion.
  6. Both forces act on the book, so they are not a Third Law pair · A Third Law pair needs two different objects. Here, both forces act on the book, so they're balanced forces, not a pair.
  7. It is 60 N in the forward direction · The reaction matches the action exactly: 60 newtons, in the opposite direction. The wall being still and the swimmer speeding up change nothing about that.
  8. False · The forces must also come from the same interaction, with the same two objects exerting them on each other. Unrelated forces can have equal sizes and opposite directions.
  9. 150 · Newton's Third Law: the reaction force always matches the action force in size, just in the opposite direction.
  10. Sam's push and the supports' forces can balance on the wall · Sam's push still acts on the wall. Forces from the supports can balance it. The wall's partner force on Sam acts on Sam, so it cannot balance forces on the wall.
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