Everyone knows bowling balls are for knocking things down. But it turns out they're also pretty good at shoring up our knowledge of basic physics. Just have a look at this strangely hypnotic YouTube video showing a line of bowling balls on strings swinging back and forth like pendulums.
At the start of the "Pendulum Wave Demonstration" video, which was posted on Sept. 7 by YouTube user Maria Ikenberry, the balls swing side by side. But slowly they drift out of phase to form a wavelike pattern--because the strings that hold them are of different lengths and thus cause the balls to swing at different speeds. Then, amazingly, the balls fall back into phase at about 2:40.
What's going on here?
"It's something like if you had a whole bunch of clocks but each one was a little slower than the next," Dr. Jordan Ellenberg, a professor of mathematics at the University of Wisconsin and the author of How Not To Be Wrong told The Huffington Post in an email. "They would start in phase, then slowly drift out of phase--but if you chose the differences in speeds carefully, there would be a moment at some point later in the cycle where they all came into phase again."
You have to see it to believe it.