Newton’s cradle: conservation of momentum
One ball strikes a row and exactly one ball swings out from the other end. An interactive Newton’s cradle — a lesson on momentum and energy.
Press “Run”. Bodies move by the laws of physics: gravity, friction, elasticity.
What the experiment shows
Five balls hang touching each other. The left one is pulled aside and released: the impact travels through the row and the right ball flies out while the middle ones barely move.
How to run it
- Press “Run” and see how many balls move.
- In the editor lift two balls at once — how many swing out the other side?
- Make one ball heavier and see how the picture changes.
Questions to discuss
- How does the impact pass through the middle balls?
- Why do the swings slowly die out?
The science
In an elastic collision of identical bodies both momentum and kinetic energy are conserved, so the balls “swap” velocities: the moving ball stops and the resting one takes its speed. Damping comes from imperfect elasticity and friction losses.
Try it at home
Slide a coin along a table into a row of four touching coins — exactly one flies off the far end. It shows how an impact is “passed on”.
What to change in the editor
- Lift two balls instead of one.
- Lower elasticity to 0.6 — the balls will stop passing the impact cleanly.