Newton's Pendulum

About this page

Above is a GPU-accelerated, real-time visualization of Newton’s Pendulum (also called Newton’s Cradle), a classic physics demonstration of conservation of momentum and conservation of energy. When one or more balls on one side are lifted and released, an equal number of balls on the opposite side swing out with almost the same speed.

What you’re seeing

Newton’s Pendulum consists of identical steel balls suspended so that they barely touch at rest. When a ball is lifted and let go, it collides with the next ball, transferring its momentum and kinetic energy through the stationary balls in the center. The ball on the opposite end receives nearly all of that energy, swinging outward in response.

In a perfectly elastic collision with no losses, this transfer would continue indefinitely. In reality, some energy is lost to sound, heat, and slight deformations of the balls, so the motion gradually slows. This simulation exaggerates elasticity for clarity, but still includes a subtle damping effect to show realistic decay over time.

Physics behind it

The behavior of Newton’s Pendulum can be explained using two main laws:

• Conservation of Momentum: The total momentum of the system remains constant in an isolated set of collisions.
• Conservation of Energy: In elastic collisions, the total kinetic energy is conserved.

Because the balls are identical and collisions are nearly head-on, the momentum and energy transfer efficiently from the first ball to the last with minimal motion of the intermediate balls.

Observing the simulation

Try lifting different numbers of balls on one side — one ball will make one swing out, two will make two swing out, and so on. Watch for how the speed and height match on both sides, and how the motion gradually fades as energy is dissipated. This makes Newton’s Pendulum both a beautiful desk ornament and a perfect introductory physics experiment.

Tech notes

The simulation runs in WebGL2 by default, using a simple rigid-body physics solver to handle collisions and momentum transfer. Ball motion is calculated in real-time with constraints to maintain their suspension geometry. Soft shadows and reflections are used to make the balls appear metallic and physically present. On supported systems, enabling WebGPU may improve performance and allow for more accurate collision resolution.