Thanos, the supervillain in Marvel’s “Avengers: Infinity War,” uses a simple gesture—the snap of a finger—to wipe out half of all life in the universe. It then prompted one group of scientists to ask, “What is the physics of a finger snap?”
As Live Science reported, researchers at the Georgia Institute of Technology used high-speed cameras and state-of-the-art force sensors to record the speed and acceleration of finger-snapping and investigate the little-known physics that makes it possible. They discovered that a finger snap is the fastest human body acceleration ever measured. They also uncovered the best physical explanation for how snaps occur and its most essential component: friction.
“For the past few years, I’ve been fascinated with how we can snap our fingers,” said co-author Saad Bhamla, a professor in the School of Chemical and Biomolecular Engineering at the Georgia Institute of Technology. “It’s really an extraordinary physics puzzle right at our fingertips that hasn’t been investigated closely.”
Their findings, which were published in the Journal of the Royal Society Interface on Nov. 17, show that the finger snap’s maximum rotational velocities are 7,800 degrees per second and the maximum rotational acceleration is 1.6 million degrees per second squared, which is three times the acceleration produced by a professional baseball player’s arm.
This research is a significant step toward a better understanding of the motion principles at work in other living organisms and the development of more lifelike robots.
“When I first saw the data, I jumped out of my chair,” said Bhamla. “The finger snap occurs in only seven milliseconds, more than twenty times faster than the blink of an eye, which takes more than 150 milliseconds.”
After watching the 2018 Marvel Studios movie “Avengers: Infinity War,” in which Thanos, an 8-foot (2.4 meter) purple warlord from Saturn’s moon Titan, seeks out six powerful “Infinity Stones” that will grant him the ability to bend and reshape the fabric of the universe according to his will, Bhamla was inspired to conduct research. Thanos planned to wipe out half of all living species in the cosmos with a single snap of his fingers by placing the stones in a metal “Infinity Gauntlet.”
“We got into this heated debate, trying to understand if he could actually snap or not,” Bhamla said. “This is how this whole thing got started, because we want to figure out the key ingredients required to snap our fingers.”
However, performing a finger snap while wearing a metal gauntlet was a step too far for some of the scientists.
“The compression of the skin makes the system a little bit more fault tolerant,” explained co-author Elio Challita, a doctoral student at Georgia Tech. “Reducing both the compressibility and friction of the skin make it a lot harder to build up enough force in your fingers to actually snap.”
Surprisingly, using rubber coverings to increase friction on the fingertips actually lowered velocity and acceleration. As a result, too much or too little friction can reduce snap speed and acceleration, Earth.com reported.
“Based on ancient Greek art from 300 B.C., humans may very well have been snapping their fingers for hundreds of thousands of years before that, yet we are only now beginning to scientifically study it,” Bhamla said. “This is the only scientific project in my lab in which we could snap our fingers and get data.”
According to the study, finger snaps work by using arm muscles as a motor to load elastic potential energy into spring-like tendons in the fingers and arms, which is then quickly released to cause the amazing acceleration of the snap. By wedging the middle finger to the thumb and preventing it from moving, friction between the thumb and middle finger serves as a critical latch. The friction is overcome once enough energy has been built up, and the thumb and middle finger slip past each other, releasing the snap.
“We need this Goldilocks zone, because too little friction, you can’t load up enough energy,” says Bhamla. “But if you have too high friction, you still have to have this dynamic motion of sliding past each other.”
“Fingers snapping is a really high, fast motion and extreme case, which allows us to peer into the limits of these finger pads,” says Bhamla.