Snap! High-speed video captures the physics of snapping fingers
A speedy snap takes friction plus compression of the finger pads
A snapping finger is one of the fastest rotational motions known in the human body. It’s almost as fast as some professional baseball pitchers’ arms.
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It all happens in a snap. New high-speed video exposes the blink-and-you’ll-miss-it physics behind snapped fingers.
The footage reveals the movement’s extreme speed. And it points to the key factors needed for a proper snap: friction plus compressible finger pads. The two work together, researchers report November 17 in Journal of the Royal Society Interface.
A finger snap lasts only about seven milliseconds. That’s roughly 20 times as fast as the blink of an eye, says Saad Bhamla. He’s a biophysicist at Georgia Tech in Atlanta.
Bhamla led a team that used high-speed video to study the motion. After slipping off the thumb, the middle finger rotates at a rate up to 7.8 degrees per millisecond. That’s nearly what a professional baseball pitcher’s arm can achieve. And a snapping finger accelerates almost three times as fast as pitchers’ arms.
The scientists explored friction’s role in the snap. They covered study participants’ fingers with high-friction rubber or a low-friction lubricant. But both treatments made snaps fall flat, the team found. Instead, bare fingers provide the ideal friction for a speedy snap. Just-right friction between thumb and middle finger allows energy to be stored — then suddenly unleashed. Too little friction means less pent-up energy and a slower snap. Too much friction will hinder the finger’s release, also slowing the snap.
Bhamla and his colleagues were inspired by a scene in the 2018 movie Avengers: Infinity War. The supervillain Thanos snaps his fingers while wearing a supernatural metal glove. The move obliterates half of all life in the universe. Would it be possible to snap, the team wondered, while wearing a rigid glove? Typically, fingers compress as they press together to ready for a snap. That increases the contact area and friction between the pads. But a metal cover would block compression. So the researchers tested snapping with fingers covered by hard thimbles. Sure enough, the snaps were sluggish.
So Thanos’ snap would have been a dud. No superheroes needed: Physics saves the day.
