What is Newton's Cradle?
Newton's Cradle is a classic desk toy and physics demonstrator consisting of identical metal spheres suspended in a straight line from a rigid frame. When one or more balls on one end are lifted and released, they collide with the stationary balls and transfer their motion so that the same number of balls swing out on the opposite end.
History
Although named after Sir Isaac Newton, the device was not invented by him. The underlying principles of elastic collisions were studied in the 17th century by Christiaan Huygens, John Wallis, Christopher Wren, and especially the French physicist Edme Mariotte (around 1670), who performed experiments with suspended spheres.
The modern name “Newton’s Cradle” was coined in 1967 by English actor Simon Prebble for a commercial wooden version sold through Harrods. It quickly became a popular executive desk toy.
Physics Principles
Conservation of Momentum
Total momentum before a collision equals total momentum after.
For equal masses: if one ball hits with velocity v, one ball leaves with ≈ v.
Conservation of Energy
In an ideal elastic collision, kinetic energy is also conserved. Energy continually converts between potential (height) and kinetic (motion).
Newton’s Third Law
Action–reaction pairs: when ball A pushes ball B, ball B pushes back on A with equal force.
Real cradles slowly lose energy to air resistance, sound, heat, and imperfect elasticity, so the motion eventually dies out. The damping slider lets you control that loss.