Why does it feel like your finger is vibrating when gliding it across some phone edges or some surfaces?

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Why does it feel like your finger is vibrating when gliding it across some phone edges or some surfaces?

In: Physics

It’s the repeated transition between kinetic and static friction forces, which aren’t equal. You’re applying more pressure into the glass than along its surface. So what happens is the lateral pressure to slide your finger builds up until it overcomes the static friction and your finger starts to slip, but very quickly your finger tip tissue is “reset” and the pressure angle relaxes because the finger tip is sliding smoothly away from the previous spot. Because you’re exerting heavy downward pressure at some point friction overcomes the slide and your finger stops. It stays there until your hand catches up to the finger tip location and the lateral pressure again builds as the pressure angle adjusts and overcomes the static friction and it starts to slide again.

This occurs generally on surfaces where your skin generates fairly decent static friction to grip something, but the kinetic friction is quite a bit lower once it starts sliding. Because those two frictional forces are so different, it creates that chattering or buzzing sensation when the swap between stationary static friction and sliding kinetic friction occurs rapidly.