Home / Topics / Momentum & Collisions
Newton's cradle
Beginner
A row of steel balls transfers momentum from one end to the other.
Steel balls transfer momentum through the chain, so one ball swings out at the far end with the same speed. Both energy and momentum conservation are needed to explain why exactly one ball leaves.
Two balls in swing out two.
Real cradles gradually lose energy.
In more detail
Newton's cradle shows momentum and energy conservation with identical steel balls. Lifting one ball and releasing it transfers momentum through the chain, sending one ball out the other end.
Real-world uses
- Demonstrating conservation of momentum in classrooms.
- Engineers use similar chain-of-impact ideas for shock absorbers.
- A row of identical steel balls in a cradle shows momentum and energy being passed along the row with little loss.
Open the interactive lesson, with simulation and quiz →
Frequently asked questions
Why does only one ball swing out?
Because equal masses in an elastic collision exchange velocities, so the momentum passes through to the last ball.
Does it run forever?
No. Small losses to heat and sound eventually stop it.
Why does only one ball swing out at the end?
Each collision transfers the same momentum through the row, so the same momentum and energy come out at the other end.
Related topics in Momentum & Collisions
Kepler's second law from L · Collision of particles in physics labs · Compton scattering · Momentum of light · Radiation pressure · Momentum in fluids