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 slows down
   • Balanced; it must stop
   • Unbalanced; it speeds up
   • Balanced; it keeps the same speed
6. 5.

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

   • Unbalanced; it starts moving right
   • Balanced; it moves at a steady speed
   • Balanced; it stays still
   • Unbalanced; it moves left
7. 6.

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

   • A force that pushes moving things forward
   • How much an object resists a change in motion
   • How fast an object is moving
   • The force that slows a sliding object
8. 7.

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

   • Neither, since inertia is a push
   • The empty one, since it is easier to swing
   • The full one, since it has more mass
   • The one swung faster
9. 8.

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

   • It feels no friction
   • It is hard to start or stop
   • It rolls very fast
   • A force inside it keeps pushing it
10. 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 speeds up a little
    • It stops soon, since forces balance
    • It slows down, since it needs more push
11. 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 needs a push to stay put
    • It sinks into the desk