Why do basketball shoes squeak? Its related to the lobster violin earthquake.

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 Why do basketball shoes squeak? Its related to the lobster violin earthquake.


Sound of sneakers rubbing the floor (Source: Netease Sports)

Perhaps everyone who has a general knowledge of physics will answer that the sound of sneakers on the floor is due to friction. But why does friction make such a noise? This requires some scientific inquiry, and to most peoples surprise, it has something to do with lobsters, violins and earthquakes.

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Sound of Broken Groove Lobster (Source: Netease Sports)

According to Sila Patek, a biologist at Duke University in the United States, a species called Broken Lobster has a natural skill. When it tries to frighten off its natural enemies, it rubs its smooth and elastic protuberance at the base of its tentacles against its smooth and hard crustacean head, making a tremendous noise. This phenomenon can be called stick-slip phenomenon: when two relatively smooth or flat surfaces contact each other, the cyclic phenomenon of sliding-bonding-sliding occurs under the action of stress, and the whole process will produce vibration and often accompanied by sound.

The stick-slip phenomenon can be used to explain a variety of phenomena in life, such as why brakes produce abnormal sounds, and violinists can make wonderful music by gently pulling the bow on the strings. Basketball shoes rub on the floor because they squeak. The stick-slip motion of friction between shoes and floor, which is similar to the principle of earthquake, is caused by the relative motion of sliding-locking-sliding in the process of sliding.

Research shows that the stick-slip movement on the basketball court usually occurs at the moment when the foot of the player has just landed or started. For a basketball shoe, its grip must be properly designed - if the grip is too strong, the wearers technical movements will become uncoordinated; if the grip is insufficient, it will increase the risk of slipping. Therefore, excellent footwear designers always regard this kind of friction sound as the best signal of balance of footwear grip.

The results of vibration experiments tell us that compressed air is the fundamental way to make sound. And the soles of our common basketball shoes are always distributed with various lines, thus forming a large number of tiny voids in the soles, so the air can easily be compressed, resulting in sound waves.

The audio produced by friction between the shoes and the floor is close to the human auditory upper limit, and even enlarged by the hardwood floor used in the gymnasium. Therefore, without noise interference, the friction and squeaks can be heard in the stadium, which has become the most familiar melody for the fans watching the game.

Note: The data are from the New York Times article by John Branch.