Forces and Motion: Balance, Patterns and Gravity

A tug-of-war rope that does not move, a swing that goes back and forth, an apple that falls from a tree: forces are everywhere. Let’s find out when forces balance each other, how a repeating motion helps us predict what comes next, and which force pulls everything down.

This lesson takes about 10 minutes. You can take a break after each part.

Before you start

Forces and Motion: Balance, Patterns and Gravity

Learning objectives

  • I can tell balanced forces from unbalanced forces and say how the motion changes.
  • I can use a repeating motion, like a swing, to predict what comes next.
  • I can explain that gravity pulls objects down, toward the center of the Earth.

Balanced or unbalanced?

Forces that cancel, forces that win

A force is a push or a pull, with a strength and a direction.

Balanced forces cancel each other: the motion does not change. With unbalanced forces, the stronger one wins: the object starts, stops, speeds up or changes direction.

Two teams of three children pull a rope in opposite directions. The arrows of both teams have the same length, and the flag in the middle of the rope stays above the center line.
Both teams pull just as hard: the forces are balanced and the rope does not move.
The same two teams pull the rope. The arrow of the right team is longer, and the flag on the rope has moved past the center line toward the right team.
One team pulls harder: the forces are unbalanced and the rope moves toward the stronger team.

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Motions that repeat

When a motion repeats

Some motions repeat the same way again and again: a swing goes forward and back, a marble rolls from one side of a bowl to the other, a seesaw goes up and down.

This repeating motion is a pattern. When we observe a pattern, we can predict what the object will do next.

Children play at a park. Two of them ride a swing that goes forward and back, while another boy pulls a red wagon full of toys on the grass.
A swing goes forward and back, again and again: its motion repeats in a pattern.

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Gravity pulls down

The force that pulls everything down

When you let go of a ball, it falls. A force pulls it: gravity, the pull of the Earth. Gravity pulls every object, even when nothing touches it.

Gravity always pulls toward the center of the Earth. So everywhere on our round planet, “down” means toward the ground under your feet.

Three small pictures. 1: an apple falls from a tree branch, an arrow points down. 2: a horseshoe magnet pulls nails toward it. 3: a balloon makes a child's hair stand up.
Gravity pulls the apple down without touching it. Magnets and a rubbed balloon also act from a distance.

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Review game

Final assessment

To master the lesson, you need at least 60% correct answers.

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Summary

  • A force is a push or a pull, with a strength and a direction.
  • Balanced forces do not change the motion; unbalanced forces make an object start, stop, speed up or change direction.
  • A motion that repeats, like a swing, is a pattern: it helps us predict what comes next.
  • Gravity pulls every object down, toward the center of the Earth.

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