"Terrifying juggling machine can toss around five billiard balls at once"

 Terrifying is right. The sound! Meaninglessly juggling into infinity, or until the grid fails.

Within the story there are videos that make the article clearer.  Also comments, one or two noting that the machine drops a ball at the minute mark, which is sort of comforting.

Long ago at the Museum of Science and Industry in Chicago there was a beautiful display illustrating something or other in physics. It was a small box say 3ft square with a window. from a hole on one side a steel ball dropped down to a steel plate, which was tilted at an angle such that the ball bounced high enough to put it into a hoe on the other side, where it apparently went down an inclined track to come out again from the first hole, and repeat. There were actually several balls continuing this process. I think there was more than one steel plate and more than one bounce, but I can't remember. And I thought That will go on forever and never stop. My first moment of ontological-existential terror (or delight, hard to say).

This comes to me via Paul diFilippo who likes to send me scary machines.  I mean images of them.  he has yet to send me an actual one.

io9.com/5806648/terrifying-juggling-machine-can-toss-around-five-billiard-balls-at-once