"Newton's laws of motion explained for kids" is typed by parents helping with a science project and by children who have been told the three laws and cannot see why they are true. This page explains each law in plain words with one everyday example, gives three experiments you can do with things in the kitchen, names the four mistakes almost every child makes (one of them is the whole reason physics is hard), and ends with a free worksheet with answers. It is written for ages 8 to 13 and for the parent sitting next to them.
The three laws in plain words
First law: things keep doing what they are doing. A ball on the floor stays still until something moves it. A ball that is rolling keeps rolling, in a straight line, at the same speed, until something changes that. The something is a force: a push, a pull, friction, gravity. The name for this stubbornness is inertia.
The everyday example is a seatbelt. When a car stops suddenly, the car stops but your body does not, because nothing has stopped it yet; it keeps moving forward at the speed the car had. The seatbelt is the force that stops you. Without it, the windscreen would be.
Second law: harder push, faster speed-up; heavier thing, slower speed-up. Push a shopping trolley gently and it speeds up slowly; push it hard and it speeds up fast. Now fill it with shopping: the same push speeds it up less. In symbols, force = mass ร acceleration, or F = ma. "Acceleration" is how quickly the speed changes, not the speed itself; a car going steadily at 100 km/h has no acceleration.
Third law: every push has a push back. When you push a wall, the wall pushes your hands with exactly the same force; that is why your hands feel it. When a rocket pushes hot gas downward, the gas pushes the rocket upward. When you jump, you push the ground down and the ground pushes you up. The two pushes are always equal, always opposite, and always on two different things.
Newton's first law, stated properly
The first law is the one searched for most (about 64,000 times a month in the US alone) and the one most often misquoted, so here it is in full. An object stays at rest, or keeps moving in a straight line at a constant speed, unless a net (resultant) force acts on it. Three things in that sentence matter:
- Constant speed in a straight line counts as "no change". A car cruising at a steady 100 km/h on a straight motorway has balanced forces on it: the engine's push equals friction plus air resistance, the net force is zero, and the first law says it carries on. Children expect a moving car to need a net force; it needs one only to speed up, slow down or turn.
- It is the net force that matters, not any single force. A book on a table has two forces on it, its weight down and the table's push up; they cancel, the net force is zero, and the book stays put. Our net force page shows how to add the forces.
- Inertia is the tendency to keep doing what you are doing, and mass measures it. A full shopping trolley is harder to start and harder to stop than an empty one; a bowling ball resists a push more than a football. Inertia is not a force; it is the property that makes a force necessary.
| Example | What the first law says is happening |
|---|---|
| Passengers lurch forward when a bus brakes | the bus stops; the passengers keep moving until the seat or the strap stops them |
| Ketchup comes out when you jerk the bottle and stop it | the bottle stops; the ketchup keeps moving |
| A tablecloth pulled fast leaves the plates in place | the cloth moves; the plates' inertia keeps them where they were, friction being too brief to move them |
| A puck slides a long way on ice | almost no friction, so almost no net force, so almost no change in motion |
| A satellite orbits for years with its engine off | no air resistance; the only force, gravity, bends the path but no force is needed to keep it moving |
| Dust flies off a carpet when you beat it | the carpet moves; the dust stays and the carpet leaves it behind |
The law is sometimes called the law of inertia, and in exam language the three forms are: an object at rest stays at rest; an object in motion stays in motion at constant velocity; both unless acted on by a resultant force.
Three experiments with kitchen objects
| Experiment | What to do | What happens, and which law |
|---|---|---|
| Coin and card | Balance a playing card on a glass and a coin on the card. Flick the card away sideways, fast | The coin drops straight into the glass: nothing pushed the coin sideways, so it stayed where it was, then gravity pulled it down. First law |
| Balloon rocket | Thread a drinking straw on a long string tied between two chairs. Blow up a balloon, hold it closed, tape it to the straw, let go | The balloon shoots along the string. Air pushed out backwards, the air pushed the balloon forwards. Third law |
| Marble and golf ball | Put a marble and a golf ball side by side on a smooth floor. Flick each with the same finger flick | The marble speeds up far more from the same push, because it has less mass. Second law |
Do the coin trick three times with a heavier coin each time. It works better with the heavier coin, which is the first law again: more mass, more inertia.
The four mistakes every child makes
- "A moving thing needs a force to keep moving." Everyday life teaches this, because friction is everywhere: the ball on the floor stops, so surely something has to keep pushing it. The first law says the opposite: the ball stopped because friction pushed against it. Take friction away (ice, space) and it never stops. This single idea is the one most children, and many adults, get wrong, and physics from Class 9 onward assumes you have switched.
- "Heavier things fall faster." They do not, if air is not in the way; a hammer and a feather dropped on the Moon land together. The heavier thing has more force on it (gravity) and more mass to move, and the two cancel exactly. Second law.
- "The rocket pushes against the air." It does not; rockets work in space where there is no air. The rocket pushes the gas, the gas pushes the rocket. Third law, and the two forces are on different things.
- "If the forces are equal and opposite, nothing can move." The third-law pair acts on two different objects: you push the ground, the ground pushes you. The forces on you (the ground's push up, gravity down) are the ones that decide whether you move, and those are not a third-law pair.
What each law becomes later
| Law | Ages 8 to 11 | Ages 11 to 14 (KS3, Class 9, US middle school) | Ages 14 to 18 (GCSE, Class 11, AP) |
|---|---|---|---|
| First | Inertia, seatbelts | Balanced and unbalanced forces, friction as a force | Equilibrium, free-body diagrams |
| Second | Harder push, faster speed-up | F = ma with numbers, mass in kg, force in newtons | Momentum, impulse, resultant forces in two dimensions |
| Third | Push back | Action-reaction pairs named correctly | Conservation of momentum, collisions |
The Class 9 CBSE chapter "Force and Laws of Motion", the UK KS3 forces unit and the US middle-school physical science unit all teach the three laws by name for the first time; a child who arrives knowing the everyday examples and the four mistakes has already done the hard part.
The free worksheet
Fifteen questions: eight "which law is this?" situations and seven with numbers (F = ma in three forms), with answers on the second page: Newton's laws of motion for kids worksheet (PDF) (A4, two pages, free). Do the "which law" questions out loud together; the child who can name the law in a situation has understood it, which reciting the laws never proves.
Where to get help
A 1-on-1 online science class with a tutor who holds a master's in physics, from middle-school physical science to Class 9, GCSE, AP and A-level physics: the picture first, the everyday example, then the equation. The recording and notes after every class, US$10 to $13 an hour. The physics page has the courses; the free 30-minute first class is usually on forces, because that is where physics is won or lost.
Questions parents ask
1What are Newton's three laws of motion in simple words?
2What is an example of Newton's first law for kids?
3What is an example of Newton's third law for kids?
4At what age do children learn Newton's laws?
See how we teach this, 1-on-1 online โ
Shobha
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