I suppose it says something about me (and, frankly, nothing good) that I really like the trippy sensations produced by staring for way too long at these animations. Maybe I picked the wrong week to stop sniffing glue.
Try it. You are getting sleepy. Very, very sleepy. Your eyelids are getting heavy. You are falling into a deep, deep sleep. When you wake up, you will leave a comment on this post saying something nice about Niobe.
And (kind of based on the animation below) does anyone remember that toy from the 1970s that consisted of four silver balls, tied to strings and attached to a frame, which you would pull back (the balls, not the frame) then release so they would hit one another like tiny pendulums (pendula?), while you watched them swing back and forth and back and forth? Like, what the heck was it called?
eta: Newton's Cradle is apparently the (curiously apt) name I was looking for. Thank you, so, so much Jill, Betty M and Angie. And, because I know that you all want to rock your very own Newton's Cradle, while learning all about the conservation of momentum, here's a link to the interactive online version.
My only suggestion is not to create one with too many balls because, just like the real Newton's Cradle, you'll spend more time untangling than playing.
(both animations are public domain images from wikipedia commons)