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 speeds up
   • Balanced; it must stop
   • Unbalanced; it slows down
5. 4.

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

   • Balanced; it moves at a steady speed
   • Unbalanced; it moves left
   • Balanced; it stays still
   • Unbalanced; it starts moving right
6. 5.

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

   • The force that slows a sliding object
   • How much an object resists a change in motion
   • How fast an object is moving
   • A force that pushes moving things forward
7. 6.

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

   • The empty one, since it is easier to swing
   • The one swung faster
   • The full one, since it has more mass
   • Neither, since inertia is a push
8. 7.

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

   • It is hard to start or stop
   • A force inside it keeps pushing it
   • It rolls very fast
   • It feels no friction
9. 8.

   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 speeds up a little
   • It slows down, since it needs more push

10. 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.

11. 9.

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

    • It stops, since balanced means still
    • It speeds up to the right
    • It stays the same, 2 m/s
    • It slows, since it is not pushed harder
12. 10.

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

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