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

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 pulling you along the ground
    • Your leg muscles pulling your whole body forward
    • The floor pushing forward on your foot with equal force

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

    • A swimmer's feet push the wall, and the wall pushes the swimmer forward
    • A book rests on a table without moving
    • A car slows down because of friction

  3. You push a shopping trolley forward with your hands. What is the reaction force?

    • The floor pushing up on the trolley's wheels
    • The trolley rolling forward on its own
    • The trolley pushing back on your hands with equal force

  4. A rocket moves forward in space by pushing exhaust gas backward. The force on the rocket is:

    • Equal to the force on the gas but in the opposite direction
    • Greater than the force on the gas
    • Less than the force on the gas
    • Zero because there is no air in space

  5. You blow up a balloon and let it go. Air rushes out the back, and the balloon shoots forward. What pushes the balloon forward?

    • The outside air pushing the balloon from behind
    • The escaping air pushing back on the balloon with equal force
    • The balloon's rubber pulling it forward

  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 same object, the book, not on two different objects
    • The forces are not equal in size
    • Gravity does not count as a real force

  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 newtons, because the wall does not move
    • It is 60 newtons, pointing forward
    • It is more than 60 newtons, because the swimmer speeds up

  8. A swimmer pushes off the pool wall and moves forward. The wall moves backward too.

    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 wall with 30 newtons and says: "The wall pushes back weaker than 30 newtons, because it does not move." Is Sam right?

    • Yes, objects that stay still push back weaker
    • No, the wall pushes back with the full 30 newtons, even though it stays still
    • No, the wall pushes back with more than 30 newtons
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Answer key

For grown-ups. Fold this page away before handing over the rest.

Newton's Third Law W1-mt_fbYbe3YSVj-s1

  1. The floor pushing 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. A swimmer's feet push the wall, and the wall pushes the swimmer forward · The swimmer pushes the wall, and the wall pushes back on the swimmer just as hard. That's an action-reaction pair.
  3. The trolley pushing back on your hands with equal force · Your hands push the trolley forward, so the trolley pushes back on your hands just as hard. You can feel that push on your palms.
  4. Equal to the force on the gas but in the opposite direction · Newton's third law: the force on the gas and the force on the rocket are equal in magnitude and opposite in direction.
  5. The escaping air pushing back on the balloon with equal force · The balloon pushes the air out backward, so the air pushes the balloon forward with the same amount of force, like a tiny rocket.
  6. Both forces act on the same object, the book, not on two different objects · 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 newtons, pointing forward · 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 wall is attached to the Earth, so its mass is huge. It does experience an equal force, but its acceleration is too tiny to notice.
  9. 150 · Newton's Third Law: the reaction force always matches the action force in size, just in the opposite direction.
  10. No, the wall pushes back with the full 30 newtons, even though it stays still · The reaction always matches the action in size, whether anything moves or not. The wall pushes back with the full 30 newtons.
Worksheet · LightMySky