The device is named after Sir Isaac Newton and is also known as Newton’s pendulum, Newton’s rocker, and more casually, Newton’s balls. Newton’s cradle, apart from being an elegant decorative piece, also demonstrates two very important and fundamental laws of physics, namely the law of conservation of momentum and the law of conservation of energy.

History of Newton’s Cradle 

Contrary to popular belief and its naming, the swinging ball setup was not actually invented by Newton, nor was he the first to ink the laws that the toy demonstrates.

The principles demonstrated by such a cradle were first mentioned in a paper presented by John Wallis, Christopher Wren, and Christiaan Huygens to the Royal Society in the year 1662. Christiaan Huygens, in particular, contributed the most to the cradle’s invention. Huygens’ work, De Motu Corporum ex Percussione, discusses the collision of suspended bodies and the transfer of motion from a moving body to the one at rest. He was also the first to report that explaining the mechanics behind a cradle-like system required the use of conservation of momentum and a quantity proportional to mass times velocity squared. The quantity mass times velocity squared is, of course, the kinetic energy of a moving body; even so, the term was coined nearly a century after Huygens’ discovery.

On the other hand, the law of conservation of momentum was first suggested by Rene Descartes. Although, the mathematical representation he put forth incorporated speed instead of velocity. Rene’s formula, momentum = mass x speed, did work in certain scenarios, but couldn’t explain the collision of objects and the ensuing momentums. Huygens replaced speed with velocity, a vector quantity, and was therefore more successful in explaining the collision of objects.

Nevertheless, Abbé Mariotte, a French physicist & priest, was the first to properly conduct and record experiments on pendulum balls. Newton mentioned Mariotte’s work in his book, the Principia, and that’s the entirety of contribution to the setup that now goes by his name.

1687年7月5日, 英国物理学家伊萨克·牛顿创作的物理学哲学著作《自然哲学的数学原理》正式发表。拉丁文：Philosophiae Naturalis Principia Mathematica

https://www.scienceabc.com/pure-sciences/what-is-newtons-cradle-and-how-does-it-work.html