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8th grade Why things keep moving or stay still (balanced and unbalanced forces) worksheet

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

Grade 8 Science Worksheet - Challenge Me

NameDate

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. Box A: push 1 25 N pointing right; push 2 15 N pointing right; friction ? pointing left. Beside it: moving right at a steady speed.

  2. Ari and a friend push a box of books to the right at a steady speed. How strong is the friction?

  3. Use this

    Force arrow diagram, one dimension, arrows drawn to scale by size. Box A: push 1 30 N pointing right; push 2 18 N pointing right; friction ? pointing left. Beside it: moving right at a steady speed.

  4. Bo and a cousin push a big box of toys to the right at a steady speed. How strong is the friction?

  5. Use this

    Force arrow diagram, one dimension, arrows drawn to scale by size. Box A: push 1 22 N pointing right; push 2 14 N pointing right; friction ? pointing left. Beside it: moving right at a steady speed.

  6. Esme and a friend push a sled to the right across flat snow at a steady speed. How strong is the friction?

  7. A hockey puck glides across smooth ice at a steady 4 m/s. Jun says a forward force must keep pushing it. Agree or disagree?

    • Disagree: no net force is needed to keep moving
    • Agree: the force of inertia pushes it
    • Disagree: the ice pushes it forward
    • Agree: without a push it would stop

  8. An ice skater glides at 3 m/s with friction and air draw a line almost zero. Luz says the skater keeps gliding. Agree or disagree?

    • Agree: a force of inertia carries the skater
    • Agree: nothing changes the motion
    • Disagree: gliding needs a push
    • Disagree: the skater must speed up

  9. Milo pulls a wagon of books; the wagon bumps a curb and stops. The books slide forward. Why?

    • The wagon's pull is still inside them
    • A force called inertia pushes them forward
    • They keep moving; nothing stopped them yet
    • They have inertia because they move fast

  10. Pia carries an empty cup and a full cup of water and stops suddenly. Which is harder to stop?

    • The full cup, since it has more mass
    • The empty cup, since it moves faster
    • Neither, since stopping takes no force
    • Both, since inertia pushes them equally

  11. Ren stops pushing a rolling cart. Now only friction acts. What happens to the cart?

    • It keeps 2 m/s, since forces balance
    • It slows down bit by bit
    • It stops at once, with no push
    • It rolls back to the left

  12. Force arrow diagram, one dimension, arrows drawn to scale by size. Tala shoves a box to get it moving, then pushes with exactly 10 N to match friction. What happens next?

    • It speeds up to the right
    • It stops, since balanced means still
    • It keeps moving at 1 m/s
    • It slows, since 10 N is not extra push

  13. A sled glides at a steady 2 m/s while Zee pulls with 30 N against 30 N of friction. What happens next, and why?

    • It moves left: friction wins
    • It slows to a stop: balanced means still
    • It keeps gliding: no net force changes it
    • It slows: the pull adds nothing extra
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8th grade Why things keep moving or stay still (balanced and unbalanced forces) worksheet – printable
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About this worksheet

Why things keep moving or stay still (balanced and unbalanced forces). Every version has 10 questions, and the answer key prints on the second page.

What your child will learn

  • I can find the net force when forces push the same way or opposite ways.
  • I can predict motion: balanced forces mean no change (still, or steady speed); unbalanced forces change the speed.
  • I can explain inertia: more mass means more resistance to a change in motion, and inertia is not a force.

Standard: MS-PS2-2

Words to know

force: A push or a pull, measured in newtons (N)

net force: What is left when all the forces on one object are combined

balanced forces: Forces that cancel, so the net force is zero

unbalanced forces: Forces that leave a net force, so the motion changes

friction: A force that acts against sliding or rolling

inertia: How much an object resists a change in its motion

steady speed: The same speed in the same direction, moment after moment

Common mistakes

Your child added forces that point opposite ways (or subtracted ones that point the same way). Push a box together from both sides and talk about which way it goes.

Your child thought a moving thing needs a force to keep it moving. Slide a book on a smooth floor and talk about what slows it down: friction, not a lost push.

Your child thought balanced forces always mean the object is still. Point out a bike at steady speed: the forces are balanced, yet it keeps moving.

Questions parents ask

What is the most common mistake with why things keep moving or stay still (balanced and unbalanced forces)?

Your child added forces that point opposite ways (or subtracted ones that point the same way). Push a box together from both sides and talk about which way it goes.

Are these 8th grade science worksheets free to print?

Yes. All 6 printable versions at each level are free to print, with the answer key, and no account is needed.

More grade 8 science

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