Action
If one ball is pulled away and is let to fall, it strikes the first ball in the series and comes to nearly a dead stop. The ball on the opposite side acquires most of the velocity and almost instantly swings in an arc almost as high as the release height of the Last ball. This shows that the final ball receives most of the energy and momentum that was in the first ball.
The impact produces a shock wave that propagates through the intermediate balls. Any efficiently elastic material such as steel will do this as long as the kinetic energy is temporarily stored as potential energy in the compression of the material rather than being lost as heat.
Intrigue is provided by starting more than one ball in motion. With two balls, exactly two balls on the opposite side swing out and back.
More than half the balls can be set in motion. For example, three out of five balls will result in the central ball swinging without any apparent interruption.
While the symmetry is satisfying, why does the initial ball (or balls) not bounce back instead of imparting nearly all the momentum and energy to the last ball (or balls)? The simple equations used for the conservation of kinetic energy and conservation of momentum can show this is a possible solution, but they cannot be used to predict the final velocities when there are three or more balls in a cradle, because they provide only two equations to find the three or more unknowns (velocities of the balls). They give an infinite number of possible solutions if the system of balls is not examined in more detail.
Read more about this topic: Newton's Cradle
Famous quotes containing the word action:
“Insurrection:... insurrection as soon as circumstances allow: insurrection, strenuous, ubiquitous: the insurrection of the masses: the holy war of the oppressed: the republic to make republicans: the people in action to initiate progress. Let the insurrection announce with its awful voice the decrees of God: let it clear and level the ground on which its own immortal structure shall be raised. Let it, like the Nile, flood all the country that it is destined to make fertile.”
—Giuseppe Mazzini (1805–1872)
“In the life of the human spirit, words are action, much more so than many of us may realize who live in countries where freedom of expression is taken for granted. The leaders of totalitarian nations understand this very well. The proof is that words are precisely the action for which dissidents in those countries are being persecuted.”
—Jimmy Carter (James Earl Carter, Jr.)
“For the child whose impulsiveness is indulged, who retains his primitive-discharge mechanisms, is not only an ill-behaved child but a child whose intellectual development is slowed down. No matter how well he is endowed intellectually, if direct action and immediate gratification are the guiding principles of his behavior, there will be less incentive to develop the higher mental processes, to reason, to employ the imagination creatively. . . .”
—Selma H. Fraiberg (20th century)