How high is the force of snapping fingers?
Researchers from the Georgia Institute of Technology studied the physics of a finger snap and determined how friction plays a critical role. Using an intermediate amount of friction, not too high and not too low, a snap of the finger produces the highest rotational accelerations observed in humans, even faster than the arm of a professional baseball pitcher (Journal of the Royal Society Interface).
Using high-speed imaging, automated image processing, and dynamic force sensors, the researchers analysed a variety of finger snaps. According to a press release, the researchers explored the role of friction by covering fingers with different materials.
For an ordinary snap with bare fingers, the researchers measured maximal rotational velocities of 7,800 degrees per second and rotational accelerations of 1.6 million degrees per second squared. The rotational velocity is less than that measured for the fastest rotational motions observed in humans, which come from the arms of professional baseball players during the act of pitching. However, the snap acceleration is the fastest human angular acceleration yet measured, almost three times faster than the rotational acceleration of a professional baseball pitcher's arm.
Optimum friction
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 speed and acceleration, says the release. The researchers concluded that a Goldilocks zone of friction was necessary — too little friction and not enough energy was stored to power the snap, and too much friction led to energy dissipation as the fingers took longer to slide past each other, wasting the stored energy into heat.
