Why things keep moving or stay still (balanced and unbalanced forces)

Answer Key - Grade 8 Science Worksheet - Building Confidence

Circle the best answer, or write your answer on the line.

1. 1.

   Ari pushes a box of books across the floor. The forces point opposite ways, so subtract them. What is the net force?

   10 N

2. Read this first

   Use this

   Force arrow diagram, one dimension, arrows drawn to scale by size.

3. 2.

   Bo pushes a moving box across the floor. The forces point opposite ways, so subtract them. What is the net force?

   15 N
4. 3.

   Esme pushes a laundry basket across the floor. The forces point opposite ways, so subtract them. What is the net force?

   12 N
5. 4.

   Jun slides a box across the classroom floor. Are the forces balanced, and what happens to the box?

   • Unbalanced; it speeds up
   • Balanced; it must stop
   • Unbalanced; it slows down
   • Balanced; it keeps the same speed

6. Use this

   Force arrow diagram, one dimension, arrows drawn to scale by size. Box A: pull 12 N pointing right; friction 12 N pointing left. Beside it: rolling right at a steady speed.

7. 5.

   Kira pulls a wagon along the sidewalk. Read the arrows. What happens to the wagon's motion?

   • It slows, since the pull is used up
   • It keeps rolling at the same speed
   • It speeds up to the right
   • It stops, since the forces are balanced
8. 6.

   Milo matches science words for a quiz. Which meaning goes with inertia?

   • How fast an object is moving
   • A force that pushes moving things forward
   • How much an object resists a change in motion
   • The force that slows a sliding object
9. 7.

   Noah swings an empty backpack and a full one. Which has more inertia?

   • The full one, since it has more mass
   • The empty one, since it is easier to swing
   • The one swung faster
   • Neither, since inertia is a push
10. 8.

    Pia reads that a bowling ball has a lot of inertia. What does that mean?

    • It rolls very fast
    • It is hard to start or stop
    • It feels no friction
    • A force inside it keeps pushing it
11. 9.

    Ren bikes at a steady 5 m/s. The forces on the bike balance. What happens next?

    • It stops soon, since forces balance
    • It speeds up a little
    • It slows down, since it needs more push
    • It keeps going 5 m/s

12. Use this

    Force arrow diagram, one dimension, arrows drawn to scale by size. Box A: push from the wind 3 N pointing right; water drag 3 N pointing left. Beside it: moving right at a steady 2 m/s.

13. 10.

    Tala's toy sailboat crosses a pond at a steady 2 m/s with balanced forces. What happens to its motion?

    • It stays the same, 2 m/s
    • It stops, since balanced means still
    • It speeds up to the right
    • It slows, since it is not pushed harder