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.

This high-speed video shows how a finger snap happens. The middle finger releases pent up energy as it slips off the thumb, hitting the palm at high speed roughly seven milliseconds later.

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.

Science News physics writer Emily Conover studied physics at the University of Chicago. She loves physics for its ability to reveal the secret rules about how stuff works, from tiny atoms to the vast cosmos.

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