Because science.
This pendulum wave contraption - made up of 16 bowling balls hanging from a giant wooden frame - sits in the grounds of a house in the mountains of North Carolina.
As Maria Ikenberry, who uploaded the video to YouTube, explains: "The length of time it takes a ball to swing back and forth one time to return to its starting position is dependent on the length of the pendulum, not the mass of the ball. A longer pendulum will take longer to complete one cycle than a shorter pendulum. The lengths of the pendula in this demonstration are all different and were calculated so that in about 2:40, the balls all return to the same position at the same time."
And as you can see, it's pretty amazing when they do so.
"There are some small scale versions of this demonstration that can be purchased commercially," she adds, "but if you want a 20’ version like this, you’ll have to make your own!"
(Via Colossal)