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The Physics of Newton's Cradle



We've all seen it - that contraption with 5 metal balls hanging side by side on strings? You lift one to the side as if it were a pendulum, let it go, and it swings into the others - causing the ball on the very opposite side to go up. This is called Newton's Cradle, named after the big guy himself.

There are a number of physics laws at work here. First, the law of conservation of energy: as potential energy is maximized and kinetic energy is zero when the end balls swing to their highest point, thus kinetic energy is maximized and potential energy is zero at the bottom of its path. However, while kinetic energy is maximized, the ball is suddenly stopped short by the next ball at rest at the bottom of this path.

The end sphere stops moving and it's kinetic energy becomes zero, but since the law of conservation of energy states that energy cannot be created or destroyed, that energy has to go somewhere. So it goes into the second sphere, on into the third, fourth, and finally transferred into the fifth where this ball uses the transferred kinetic energy to move away from the pack in a pendulum-like arc upward, mirroring the first sphere's movements.

Voila! Conservation of energy at its finest, explaining cool doo-hickies like Newtons Cradle. There's more physics to this contraption, but I think I'll expand on it more in my next blog post.

Thanks for reading!

Until next time,



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