Newton’s Cradle Simulator | Free Physics Tool – Eduqia
Newton's Cradle, made to play with.
Drag a ball, let go, and watch momentum travel through the row. One ball in, one ball out. Two in, two out. Physics you can feel.
The golden rule of the cradle, in one line.
1 ball in, 1 ball out. The middle balls stay almost still.
What is a Newton's cradle?
A Newton's cradle is a row of identical steel balls hung on strings. When you swing one ball into the row, one ball swings out on the far side. It shows that momentum and energy stay the same in nearly elastic collisions.
Try these 3 experiments
Each one takes 5 seconds. Tap a card and watch what changes.
1 ball in
Pull 1 ball and release it. Only the last ball swings out, almost to the same height.
2 balls in
Pull 2 balls and release them together. Now 2 balls swing out on the other side.
Heavy ball
Make the first ball 4 times heavier and release it. Several light balls fly out at once.
How to use the simulator
Press Release, or drag
Tap Pull 1, 2, or 3, or drag any ball with your mouse or finger and let go.
Predict first
Before you release, guess how many balls will swing out. Then check.
Change one setting
Lower elasticity, raise air drag, or change gravity, and watch the motion fade or speed up.
How a Newton's cradle works
Think of a line of shopping carts parked nose to nose. Shove the first cart and the last cart rolls away, while the middle ones barely move. Each cart passes the push to the next one almost instantly. The steel balls do the same with each collision.
Two rules decide the result. Momentum is mass times velocity. Kinetic energy is half the mass times velocity squared. In a perfectly elastic collision, both stay the same before and after.
Test the idea with one ball in. It carries momentum mv and energy 1/2 mv2. If two balls left at half speed, momentum would match, but the energy would drop to half. Only one ball leaving at full speed keeps both numbers equal. That is why the cradle always sends out the same number of balls that hit it.
What you will learn
Four big physics ideas, hidden inside a desk toy. Tap a card, the lesson below changes.
Conservation of momentum
Momentum is mass times velocity. The moving ball passes its momentum through the row to the last ball.
p = m x vConservation of energy
In a perfect cradle, the swinging ball loses almost no energy, so the last ball rises almost as high as the first ball started.
KE = 1/2 x m x v2Elastic collision
The balls bounce off each other with almost no energy lost as heat or sound. That is why the motion keeps going.
e = 99% in steelWhy do the middle balls stay still?
They do move, but only a tiny amount. Each one passes the push to the next ball almost at once, so you barely see them move.
1 in = 1 outConservation of momentum
Try it above: pull 1 ball. It has momentum p = m x v. That push does not disappear in the middle, it travels ball to ball, and the last ball leaves with the same momentum. That is why 1 ball in means 1 ball out.
Experiments to try
- Lift 2 balls and count how many swing out.
- Set elasticity to 80% and watch several balls start to move together.
- Use 3 balls, then 7 balls, and compare the click rhythm.
- Drag a middle ball sideways and see how its neighbours react.
- Raise the first ball's mass to 4x and release it. Several light balls fly out at once.
- Cut gravity to 0.4x for a floaty moon swing, or raise it to 2.5x for a fast rattle.
Newton's cradle questions
Why does only one ball swing out?
Only one outcome keeps both momentum and kinetic energy the same. One ball in means one ball out at the same speed.
Why does a Newton's cradle stop?
Air drag, sound and tiny energy losses in each collision turn motion into heat. Steel balls are very elastic but not perfectly elastic.
What happens if you lift two balls?
Two balls swing out on the other side at the same speed as the two that hit.
Is a Newton's cradle a perpetual motion machine?
No. Friction and air drag remove energy, so the cradle always slows down and stops.
How can teachers use this in class?
Show it on a projector, ask students to predict the result, then press Pull. Change one setting at a time and ask students to explain each change.
Learn physics by playing.
Start with 1 ball, then try 2 and 3. The pattern is the lesson.