Balanced & Unbalanced Forces · seed 1 · A4, ink-friendly. The answer key prints on its own page for grown-ups.

Balanced and unbalanced forces

Science · Forces & Motion · ages 8-9
Name ______________________   Date ____________

  1. The chart shows all horizontal forces on a sliding book. The other forces cancel. Which description fits?

    Push right6Frictionleft6
    • Balanced; speed stays the same
    • Unbalanced; speed increases
    • No forces; speed stays the same

  2. Push and friction are a toy car's only horizontal forces, and they balance. The push is 9 to the right. What is the friction force?

    • Size 9 to the right, with the push
    • Size 9 to the left, against the push
    • Size 0, with no opposing horizontal force

  3. Repeating the same force test and recording every result helps you see whether an observation happens again.

    Circle one:   True   False

  4. Two forces on a box are equal in size and point in opposite directions. What are these forces called?

    • Balanced forces
    • Unbalanced forces
    • Friction forces

  5. You want to test how push size changes a toy car's motion. Start each trial the same way and push for the same time. Which plan is fair?

    • Use one car on one floor; vary only the push size
    • Use different cars on different floors; vary the push size
    • Use one car on different floors; keep the push size fixed

  6. Ana and Bo each push the same box to the right with force 6. Are these two pushes balanced with each other?

    • Yes; two equal pushes in any direction always cancel
    • Yes; two people pushing always balance each other
    • No; equal pushes in the same direction add

  7. The greatest friction that can hold a still box is 6 units. Push and friction are its only horizontal forces. What is the smallest whole-number push, in units, that starts sliding?

    Answer: ______________

  8. A still book stays still while you push it gently. Your push and friction are its only horizontal forces. What does this tell you?

    • Friction matches your gentle push
    • Friction is greater than your push
    • Friction has disappeared completely

  9. In repeated fair tests, a still box stays still at pushes of 3, 5 and 6 units, but starts sliding at 7. Push and friction are the only horizontal forces. What range fits its greatest friction while still?

    • At least 6 but less than 7 units
    • At least 1 but less than 2 units
    • At least 9 but less than 10 units

  10. Mia tests push size. She pushes a light box on wood with force 6, then a heavy box on carpet with force 9. The heavy box travels less far. Can she conclude that bigger pushes cause less travel?

    • Yes; the larger push proves that push size caused the shorter travel
    • Yes; comparing different boxes and floors removes all other possible causes
    • No; changing the box and floor too hides the cause
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Answer key

For grown-ups. Fold this page away before handing over the rest.

Balanced and unbalanced forces W1-mt_3WMADSy0mA-s1

  1. Balanced; speed stays the same · The two horizontal forces are equal and opposite. They cancel, so the sliding book keeps the same speed and direction.
  2. Size 9 to the left, against the push · To balance the rightward push of 9, friction must have size 9 and point left.
  3. True · Repeated trials let you compare observations under the same conditions. Keep every result, including any that differ.
  4. Balanced forces · These two forces are balanced with each other: their equal sizes and opposite directions make the pair cancel. This does not tell us whether other forces act on the box.
  5. Use one car on one floor; vary only the push size · To test push size, change that alone. Keep the car, floor, starting conditions and push time the same.
  6. No; equal pushes in the same direction add · Both pushes point right, so they add to 12 right. They do not cancel each other.
  7. 7 · A push of 6 can still be balanced. The push must exceed 6, and the smallest whole number above 6 is 7.
  8. Friction matches your gentle push · The book's horizontal motion does not change. Friction matches the gentle push in size and acts in the opposite direction.
  9. At least 6 but less than 7 units · Friction could match a push of 6, but could not hold the box against 7. Its greatest value while still is at least 6 and less than 7 units.
  10. No; changing the box and floor too hides the cause · The box, floor and push size all changed. The shorter travel cannot be attributed to push size alone.
Worksheet · LightMySky