Forces: what a push or a pull actually does
A force is just a push or a pull. What matters is whether the forces on an object are balanced — that single idea decides whether anything speeds up, slows down, or stays still.
A force is simply a push or a pull. We measure it in newtons (N), and it can do three things to an object: start it moving, stop it, or change its direction or shape. But the question that matters most is whether the forces are balanced.
Balanced vs unbalanced — the whole topic in one idea
Every object usually has more than one force on it at once. What counts is the overall push once you've combined them:
- Balanced forces (they cancel out) → no change. A still object stays still; a moving one keeps moving the same way.
- Unbalanced forces (one side wins) → the object speeds up, slows down, or changes direction, in the direction of the bigger force.
A book resting on a table has gravity pulling it down and the table pushing it up, equally. Balanced — so it stays put. It isn't that there are no forces; it's that they cancel.
Forces you'll meet
| Force | What it is |
|---|---|
| Weight (gravity) | The pull of the Earth, always downward |
| Friction | Resists sliding, acts against motion |
| Air resistance | Friction from air, on moving objects |
| Tension | The pull in a stretched rope or string |
| Upthrust | The upward push of a liquid on something floating |
Friction: the helpful villain
Students think friction only slows things down. But friction is also why you can walk — your shoe grips the floor instead of sliding. Without it you couldn't start, steer, or stop. It opposes sliding, which is often exactly what you want.
Draw the arrows before you decide what happens. Sketch the object, draw one arrow for each force, and make the bigger ones longer. If the arrows balance, nothing changes. If they don't, the object accelerates the way the leftover arrow points.
Last revised 5 December 2024.