# Fall Into A Trance Watching This Pendulum Wave Of Bowling Balls

Because a pendulum's oscillation frequency depends on its length, not its mass, you can use different colored bowling balls for a pretty effect.

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Happy Monday! How about some simple physics to get your day started? We very much enjoyed this video, posted yesterday, of a giant outdoor DIY pendulum toy made with bowling balls. The toy even makes music, via pipes mounted in the ground. Cute!

The structure works just like smaller pendulum wave toys. Each bowling ball’s string is a slightly different length, with the shortest string mounted at one end of the series, the next-shortest string mounted next to it, and so on until the longest string is found at the other end. For best results, the string lengths should follow a particular formula, as described in this short paper published in the American Journal of Physics in 1991:

The ground underneath the outdoor structure is actually slanted, to accommodate the different string lengths, while keeping the bowling balls all about the same height off the ground. Jeff Goodman, a lecturer in education at Appalachian State University, designed and built the structure with friends.*

Want to make your own mesmerizing physics demo in the forest? You could start with a desktop version, so you can figure things out on a more manageable scale. There are a number of instructions online for making indoor-sized wave pendulum structures. We didn’t immediately find any instructions for a structure large enough to hold bowling balls, however, which would require a little engineering to ensure the frame is strong enough. Let us know if we’ve missed any instructions that are already out there…or if you’ve made this on your own.

*Updated September 12, 2014: We previously guessed that the top of the bowling-ball pendulum structure was slanted to accomodate the different string lengths. Goodman wrote to us to correct us. Our thanks!