5.2 What a Force Can Do

We apply forces all day without noticing — opening a drawer, stretching a rubber band, kicking a football, braking a bicycle, rolling a chapati, turning a steering handle. What do all these forces actually do?

The Four Effects of a Force A force applied on an object may:

  1. start it moving from rest (open a drawer),
  2. change its speed if it is already moving (speed up, or slow down/stop),
  3. change its direction of motion (a bat hitting a ball), or
  4. change its shape (pressing a balloon, rolling dough).

A single force can cause one or several of these effects at once. And the reverse is just as important: whenever you see a change in speed, direction or shape, a force must be acting.

Activity 5.2 — Analyse everyday forces Make a table of everyday actions and the effect of each force. For example: a friend grabbing your moving bicycle from behind is a pull that slows/stops it; hitting a moving ball with a bat is a push that changes its direction; pressing an inflated balloon is a push that changes its shape. Add your own — kicking a ball at rest, stretching a rubber band, applying brakes.

Try the sorter: for each action, pick the main effect of the force.

What does the force do?
Click each card to cycle the effect. Then press Check.

A Step Further: Objects at Rest If a book lies still on a table, does that mean no force acts on it? Not quite — it means the forces on it are balancing one another (the table pushes up exactly as hard as gravity pulls down). A still object can have several forces on it that simply cancel out. You’ll study these balanced forces in higher grades.