Action and reaction force pairs

Grade 8 Science Worksheet

Circle the best answer.

1. 1.

   A book rests on Ari's desk. Earth pulls the book down. Which force is the reaction to that pull?

   • The desk pushes the book up
   • No reaction; the forces cancel
   • The desk pushes the floor down
   • The book pulls Earth up
2. 2.

   A book presses down on Bo's desk. Which force is the reaction to the book's push on the desk?

   • The desk pushes the floor down
   • The desk pushes the book up
   • Earth pulls the book down
   • No reaction, since the book is still

3. Read this first

   Use this

   Force arrow diagram, one dimension, arrows drawn to scale by size. Box A labeled 2 kg: force from B ? pointing left. Beside it: heavy lab cart, rolling right. Box B labeled 1 kg: force from A ? pointing right. Beside it: light lab cart, at rest.

4. 3.

   In the lab, a 2 kg cart rolls into a 1 kg cart at rest. During the bump, how do the forces compare, Jun?

   • The 1 kg cart pushes harder
   • They are equal
   • The moving cart pushes; the still one can't
   • The 2 kg cart pushes harder
5. 4.

   arrows drawn to scale by size. Kira watches a fast cart catch up to a slow cart and bump it. During the bump, which cart pushes harder?

   • The slow cart, since it was hit
   • The fast cart pushes first, the slow one after
   • The fast cart, since it moves faster
   • Neither: the pushes are equal
6. 5.

   During a bump, the small cart pushes the big cart with 6 N. What force does the big cart put on the small cart, Luz?

   • 18 N, since it has three times the mass
   • 2 N, since the small cart is lighter
   • 6 N
   • 0 N, since it was pushed first
7. 6.

   Force arrow diagram, one dimension, arrows drawn to scale by size. Two skaters at rest push apart with 50 N each. Milo asks why both move. What is the best answer?

   • The ice pushes them apart
   • One skater pushes a little harder
   • Each push acts on a different skater
   • The pushes cancel, so they shouldn't move
8. 7.

   Noah's class watches a teacher launch a water rocket. It pushes water down; the water pushes it up. Why does it rise?

   • The water pushes harder than the rocket
   • It can't rise, since the pushes cancel
   • The ground pushes it up the whole time
   • The push on the rocket is not canceled
9. 8.

   A spring on a lab cart launches a ball forward; the ball pushes the cart backward. Pia asks why both move.

   • Each force acts on a different object
   • The ball pushes harder
   • Both forces are on the cart
   • The pushes cancel, so neither should
10. 9.

    Tala starts walking. The shoe pushes the ground backward. What pushes Tala forward?

    • The ground, pushing on the shoe
    • The air behind
    • Nothing; the ground doesn't move
    • The legs, pushing on the body
11. 10.

    Zee lets go of a blown-up balloon, and air rushes out the back. What pushes the balloon forward?

    • Nothing, until the air hits the wall
    • The air outside in front
    • The balloon pushes itself
    • The escaping air, pushing back