Topics · Primary Science · Interactions: Forces
Forces: pushes and pulls
A force is a push or a pull. It can start something moving, stop it, speed it up, slow it down, or change its shape or direction — and naming which of those happened is usually the question.
- 176 exam papers analysed
- appears in 97% of P6 Science papers
- ~3 min read
01 What a force can do
A force is measured in newtons (N) with a spring balance, and it always acts on something.
Five effects, and a question naming the wrong one loses the mark even when the science is understood.
- Start a stationary object moving.
- Stop a moving object.
- Speed it up or slow it down.
- Change its direction.
- Change its shape — squash, stretch or bend it.
02 The forces that get named
Papers use a small set, and each has a specific name that must be used.
| Force | Acts | Direction |
|---|---|---|
| Gravity | always, on everything | downwards |
| Friction | when surfaces rub | opposite to motion |
| Elastic spring force | when stretched or squashed | back to original shape |
| Magnetic force | on magnetic materials | towards or away |
- Gravity — pulls everything towards the Earth. It gives an object its weight, and it acts even when nothing is moving.
- Friction — acts when two surfaces rub, always opposing the motion. Rougher surfaces give more.
- Elastic spring force — a stretched or squashed elastic object pulling back towards its shape.
- Magnetic force — attraction or repulsion between magnets and magnetic materials, acting across a gap.
03 Friction, both useful and not
Friction is neither good nor bad, and questions ask for both sides.
Useful — shoe soles grip the floor, brakes stop a bicycle, a pencil marks paper. Without it you could not walk.
Unwanted — it wears moving parts out and produces heat, which is why machines are oiled and wheels are used.
More friction comes from rougher surfaces and heavier objects; less from smooth surfaces, oil, wheels and rollers.
04 Mass and weight
Mass is how much matter something contains, measured in grams and kilograms. It does not change wherever you take it.
Weight is the force of gravity on that mass, measured in newtons. It changes with the strength of gravity — the same object weighs less on the moon.
So an object taken to the moon has the same mass and less weight. Papers ask this exact question, and answering that both change, or that mass changes, is the error being looked for.
05 How to say them
These are words most children have never said out loud, and a word you cannot say is a word you avoid using. Capitals mark the syllable you lean on. Tap the speaker to hear it.
- forcemore than oneforces
A push or a pull, measured in newtons.
- newton, written NsayNYOO-tuhnmore than onenewtons
The unit force is measured in.
- gravitysayGRAV-i-tee
The force pulling everything towards the Earth. It gives an object its weight.
- frictionsayFRIK-shuhn
The force when two surfaces rub, always opposing the motion.
- mass
How much matter something contains, in grams and kilograms. It does not change with location.
- weight
The force of gravity on an object, in newtons. It changes with the strength of gravity.
- elastic spring force
The pull of a stretched or squashed elastic object back towards its shape.
06 What each level is tested on
The same topic, asked differently as it goes up. The percentage is the share of papers at that level in which it appears.
- P5
What a force is and what it can do.
Practise P5 Interactions: Forces — 10 questions →17% of P5 papers
- P6
Gravity, friction, elastic spring force and magnetic force; mass and weight; and fair tests about friction. Marked in nearly every P6 paper.
Practise P6 Interactions: Forces — 10 questions →97% of P6 papers
07 Mistakes worth knowing about
Each of these is wrong. Decide why before you open it.
“On the moon the object has less mass.”
Same mass, less weight. Mass is how much matter there is; weight is the force of gravity on it.
“Friction is always a nuisance.”
Without it you could not walk or brake. Questions usually want one useful and one unwanted example.
“The object is not moving, so no forces act on it.”
Gravity acts on everything all the time. A resting object has forces on it that balance.
“A force only makes things move.”
It can also stop them, slow them, turn them or change their shape.
“Weight is measured in kilograms.”
Weight is a force, measured in newtons. Kilograms measure mass.
Now try it
20 questions across 2 levels, marked as you go with the working shown.