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. Read this first

   Use this

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

2. 1.

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

   15 N
3. 2.

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

   12 N
4. 3.

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

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

5. 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.

6. 4.

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

   • It speeds up to the right
   • It keeps rolling at the same speed
   • It stops, since the forces are balanced
   • It slows, since the pull is used up
7. 5.

   Luz pushes a chair with wheels that is sitting still. Are the forces balanced, and what happens?

   • Balanced; it stays still
   • Unbalanced; it starts moving right
   • Unbalanced; it moves left
   • Balanced; it moves at a steady speed
8. 6.

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

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

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

   • The empty one, since it is easier to swing
   • The full one, since it has more mass
   • 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 is hard to start or stop
    • It rolls very fast
    • A force inside it keeps pushing it
    • It feels no friction
11. 9.

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

    • It keeps going 5 m/s
    • It stops soon, since forces balance
    • It slows down, since it needs more push
    • It speeds up a little
12. 10.

    A dictionary sits on Zee's desk. Gravity and the desk's support balance. What happens to the book?

    • It needs a push to stay put
    • It stays at rest
    • It sinks into the desk
    • It starts to slide