00:00You know that really horrible screech your shoes make when walking on a hard surface?
00:03Like, you're minding your own business, walking down the hall, and then suddenly
00:08turns out that scientists didn't actually know what causes this.
00:11They thought that sneakers squeaked because of stick-slip friction where an entire hard
00:15surface uniformly and repeatedly catches on another hard surface and then breaks free.
00:20Kind of like a squeaky door handle.
00:21But rubber is soft, so that doesn't fully explain this.
00:24So to figure it out, researchers used high-speed cameras to watch rubber move
00:27quickly across glass, and instead of uniformly slipping and sticking across the whole surface,
00:32the rubber would bunch up and tiny patches would slip and then move with a screech,
00:36while the rest of the rubber stayed in contact with the glass.
00:39They also found that the screech's pitch changed depending on the size and shape of
00:43the grooves in the rubber, since those ridges were channeling the pulses into repeating cycles.
00:47Sometimes the rubber's movement on the glass built up electrical energy,
00:50which caused teeny tiny lightning sparks.
00:52Figuring this out doesn't make the squeaking any less annoying,
00:55but at least we now actually know what's going on.
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