Finger Snap Physics
the science behind the fastest movement the human body can produce!
Raghav Acharya, Elio Challita and Saad Bhamla. Finger snap physics 2021 Georgia Tech.
The snap of a finger is insanely fast – faster than the blink of an eye or the pitch of a professional baseball!
The snap of a finger can reach accelerations upwards of 1.6x10^6 deg/s^2. That is faster than a professional baseball pitcher’s fastball! So, how can our fingers be so quick? And what can we learn about physics from our own bodies?
Using high-speed video and mathematical modeling, our lab began to unveil the mystery at our very fingertips. It turns out that when we snap, our fingers act like a spring-latch system. The compressibility of our fingers and the friction of our skin allows our fingers to stores and then rapidly release elastic energy, just like a mousetrap.
These observations can provide insights into the dynamics of soft robotic actuators and even for designing prosthetics!
This work has been featured ON The Late show, NPR, scientific american and more.
Major questions
1) How fast is a finger snap?
2) How do fingers snap?
3) How does skin friction and compressibility affect snap performance?
What we’ve Learnt so far
There’s a “Goldilocks zone” of friction where you can get the highest velocity snap possible.
Too much friction or too little friction, both yield poor snaps. Some friction is necessary to load energy to power the snap, but too much friction dissipates all that energy during unlatching.
Finger pad compression plays an important role in snapping
When we tried to snap using copper thimbles, we couldn’t! The natural compressibility in our fingers is necessary to engage the latch between our two fingers when we snap.
But why can humans snap?
Snapping has been a part of human culture since the ancient Greeks. However, though humans have been snapping for ages, it remains unclear if other primates like apes or chimpanzees can snap their fingers. So, it is still unclear why humans can snap!
Read the papers
The ultrafast snap of a finger is mediated by skin friction. Journal of the Royal Society Interface (2021).
A tunable, simplified model for biological latch mediated spring actuated systems. Integrative Organismal Biology (2022).
The principles of cascading power limits in small, fast biological and engineered systems. Science (2018).
What others are saying
“[the finger snap] is a great example of what we can learn with clever experiments and insightful computational modeling. By showing that varying degrees of friction between the fingers alters the elastic performance of a snap, these scientists have opened the door to discovering the principles operating in other organisms, and to putting this mechanism to work in engineered systems such as bioinspired robots.” ”
