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The principle of newtons cradle balance balls
Newtons cradle balance balls is a tabletop demonstration device invented in the 1860s in which five equal-mass spheres are held in place by slings, in close proximity to each other.
It is assumed that each metal sphere is a particle with the same mass. When a particle hits a second particle, the momentum and energy of the first particle are immediately transferred to the second, and so on, until the last particle gains momentum and energy and then pops out. The situation remains the same even if two or more particles hit the set of balls. However, instantaneous motion requires infinite acceleration and zero mass.
collision of two balls
When a moving ball hits a stationary ball, compression waves will be transmitted between the two balls.
There is a problem with newtons cradle balance balls in practice: a moving ball behaves as if its mass is concentrated in its geometric center. In an ideal newtons cradle balance balls, the metal spheres are exactly the same mass and will collide perfectly.