Newton's cradle Newton's cradle Newton’s cradle is a device that demonstrates conservation of momentum and energy using a series of swinging spheres. When one sphere at the end is lifted and released, it strikes the stationary spheres, transmitting a force through the stationary spheres that pushes the last sphere upward. The last sphere swings back and strikes the still nearly stationary spheres, repeating the effect in the opposite direction. The device is named after 17th-century English scientist Sir Isaac Newton. It is also known as Newton's balls or Executive Ball Clicker. A typical Newton's cradle consists of a series of identically sized
Energy–momentum relation Energy–momentum relation In physics, the energy–momentum relation, or relativistic dispersion relation, is the relativistic equation relating any object's rest (intrinsic) mass, total energy, and momentum: holds for a system, such as a particle or macroscopic body, having intrinsic rest mass , total energy , and a momentum of magnitude , where the constant is the speed of light, assuming the special relativity case of flat spacetime. The Dirac sea model, which was used to predict the existence of antimatter, is closely related to the energy-momentum equation. The energy–momentum relation is consistent with the familiar mass–energy relation in both its interpretations: