Why Sneakers Squeak

Have you ever wondered why sneakers make a loud squeaking(嘎吱作响) sound on the court?

Recently, scientists studied this common noise and discovered some surprising facts.

Adel Djellouli is a Harvard scientist who studies materials. As he watched a Boston Celtics basketball game, he kept noticing the squeaking sound made by the players' sneakers.

Dr Djellouli and a team of scientists decided to look into the squeaking. They slid a basketball shoe across a smooth glass plate. As the shoe slid, they took pictures with a super-fast camera and recorded the sounds that were made.

Sneaker squeaking has a lot to do with friction. Friction is the force that happens when two surfaces rub against each other. Rubber shoe soles (鞋底) on a gym floor create“stick-slip”friction. That's when two surfaces slide across each other, stick together briefly, then slip. Then stick. Then slip. And so on.

The researchers found that small areas of the shoe sole would slip and then grab again thousands of times a second. Though tiny, these vibrations were faster than the speed of sound. That repeating pattern of tiny slips causes the squeaks.

Next, the scientists tested rubbing rubber blocks against the glass. Some blocks were smooth. Others had ridges(隆起) like the bottom of a sneaker. Only the blocks with ridges squeaked.

Sneaker squeaking may not seem like serious science. However, it could actually help scientists better understand earthquakes, which also have something to do with stick-slip friction.