Question 1

How does a Newton's cradle work?

Accepted Answer

When you lift and release an end ball, it swings down and strikes the row. The impact sends a compression wave through the stationary middle balls, which barely move, and pushes the ball on the far end outward at almost the same speed. It works because momentum and kinetic energy are both conserved in the nearly elastic collisions between the identical steel balls.

Question 2

Why don't the middle balls move?

Accepted Answer

They actually do move, just imperceptibly. High-speed footage shows each middle ball shifts a tiny fraction of a millimeter as the compression wave passes through. Because the wave travels so fast and the balls are nearly perfectly elastic, the energy passes straight through to the end ball instead of staying in the middle.

Question 3

Why don't two balls launch at half speed when you drop one?

Accepted Answer

Because that would break conservation of energy. One ball out at full speed satisfies both momentum and kinetic energy at the same time, while two balls at half speed would conserve momentum but lose half the kinetic energy. The only outcome that satisfies both laws is the same number of balls leaving at the same speed.

Question 4

What happens if I lift two or three balls?

Accepted Answer

The same number swings out the other side. Lift two, two swing out. Lift three, three swing out. The system always finds the unique solution that satisfies conservation of both momentum and kinetic energy. In this simulator you drag the balls yourself — pull an inner ball outward and it carries its neighbors, so you can lift one, two, or three by hand.

Question 5

Why does a Newton's cradle eventually stop?

Accepted Answer

It is not a perpetual motion machine. Energy slowly leaves the system as sound (the audible clack), as heat from the microscopic compression of the steel, and as air resistance dragging on the swinging balls. Over time the balls all start swaying gently together and finally come to rest. You can adjust how quickly this happens with the energy loss slider, or set it to perpetual for a hypnotic, never-stopping toy.

Question 6

Who invented the Newton's cradle?

Accepted Answer

Despite the name, Isaac Newton did not build it. The collision experiments behind it date to the 1660s and the French physicist Edme Mariotte, with related work by Christiaan Huygens. The desk toy was given the name Newton's cradle by the actor Simon Prebble in 1967. It is also called Newton's pendulum, Newton's rocker, or the executive ball clicker.

Question 7

Why are the balls hung by two strings each?

Accepted Answer

The two angled strings form a V, called a bifilar suspension. This locks each ball into a single swing plane so it can only move back and forth in line with its neighbors, never twisting or swinging sideways. If a ball could move off that plane it would strike its neighbor off-center and lose energy in the wrong direction.

Question 8

Can I make a Newton's cradle GIF or wallpaper?

Accepted Answer

Yes. Open Capture in the settings panel to record the animation as an MP4 video or an animated GIF, or save a still 4K photo, in landscape, portrait, or square. The clips loop cleanly, so they work well as wallpapers, screensavers, or social posts. Everything renders on your device and nothing is uploaded.

Question 9

Is this Newton's cradle simulator free?

Accepted Answer

Yes. It is a free, browser-based Newton's cradle that runs entirely on your device with no signup and no install. You can drag the balls, orbit the 3D chrome frame, change the number of balls, toggle the sound, and record your own MP4, GIF, or 4K photo to share.

Newton's Cradle: Realistic 3D Physics Desk Toy Simulator