A new study published in the Journal of the Royal Society Interface has found that finger snapping produces the highest rotational accelerations observed in humans, even faster than the arm of a professional baseball pitcher. These findings could be potentially used in the future to devise prosthetics imitating the wide-ranging capabilities of the human hand.
“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.”
By using high-speed imaging, automated image processing, and dynamic force sensors, researchers analyzed a variety of finger snaps, and explored the role friction plays in finger snapping by covering fingers with different materials, including metallic thimbles.
The scientists measured maximal rotational velocities of 7,800 degrees per second and rotational accelerations of 1.6 million degrees per second squared for an ordinary snap with bare fingers. While the rotational velocity is slower than that of a baseball player during pitching, the snap acceleration is three times faster than that of a pitcher.
“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.”
When covering the fingers with metal thimbles, the rotational velocities decreased dramatically due to the diminished contact area between thimble-covered fingers. “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, increasing the friction of the fingertips with rubber coverings also reduced velocity and acceleration. Thus, either too little or too much friction can decrease snap speed and acceleration.
This study is an important step forward in understanding the motion principles operating in other living organism and in designing more life-like robots.
“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.”