Almost all of us can make a sharp, loud snap with our fingers. But… how exactly does that work?

There is always a moment when it comes in handy: snapping your fingers. You can grab someone’s attention in this way, or indicate the beat of music. And sometimes it has far-reaching consequences. For example, the famous snap of the finger of the villain Thanos meant the death of half of all life in the Marvel movie universe. Even though it’s become a pretty universal movement that people have been doing for centuries, we still don’t understand exactly how we do it. And so scientists decided on ‘the mystery of the snap’ a new study to demystify.

That’s how you snap your fingers!
Anyone can snap their fingers. How do you do that? Step 1: Press your thumb against your middle finger. Step 2: Fold your ring finger and pinky inward. Step 3: Build up some pressure between your thumb and middle finger. Step 4: Move the thumb from the middle finger to the index finger and hear your fingers snap.

A pressing question is why it is so difficult to explain something so ‘normal’ as a snap of the finger. “Like so much, something seems simple until we try to figure out some deep mathematical and physical logic,” said study researcher Saad Bhamla in conversation with Scientias.nl. “But we decided to study it anyway because we were curious about this strange phenomenon that many of us can. However, it took a long time to produce, test and validate a faithful mathematical model. It really is an extraordinary physics puzzle at your fingertips that has not yet been closely examined.”

slow motion

To better understand exactly how it works, the researchers filmed several people in slow motion as they snapped their fingers. And that provided a unique insight into this still enigmatic phenomenon. The researchers think that the skin on our fingers is shaped in such a way that friction creates a kind of ‘spring’. As a result, energy is built up and released quickly.

Skin

The skin plays a crucial role in this. Because when test subjects had to snap their fingers while wearing (metal) gloves – similar to those of Thanos in the Marvel film – and wearing thimbles, it turned out to be much more difficult to achieve a loud snap. With the frictional properties of a metal glove, it’s almost impossible (sorry Marvel fans). Basically, the skin is an important part of the finger snap. “By combining experiments and simulations, we found that human finger pads have optimally tuned friction and compressibility,” the researchers write. This makes the snap of a finger even one of the fastest accelerations of the human body.

Fastest acceleration

Indeed, because at a moderate amount of friction—not too high and not too low—a snap of the finger produces the highest acceleration ever seen in humans. “So that skin friction – the compressibility and friction properties – are fine-tuned, allowing us to make very fast movements,” explains Bhamla. “So fast, in fact, that it’s one of the fastest accelerations in our body, something that really surprised me. In fact, the snap of the fingers has an acceleration three times faster than the arm movement of a professional baseball player. And that while my team and I are by no means professional athletes.”

Moreover, the snap of the finger takes place within seven milliseconds. That is at least twenty times faster than blinking your eyes, which takes about 150 milliseconds.

Although, thanks to the study, we know a little better how snapping a finger works, some pressing questions also remain unanswered. One of these is, for example, why we can snap our fingers. Does it also have an evolutionary use, for example? Bhamla owes us the answer. It is also unclear whether humans are the only primates to have developed this physical ability. “A good and difficult question,” he says. “We do not know. But perhaps some readers—if they are evolutionary biologists—can provide the answer.”

Curiosity-Driven Science

According to Bhamla, the study is a good example of what he calls curiosity-driven science: studying everyday phenomena that can lead to new discoveries. And the findings may also come in handy. “We hope the study can be useful in designing prosthetics and other synthetic grippers or bio-inspired robots,” says Bhamla. “That’s because it reveals the key role of friction in powering ultra-fast motion.”

With the study, the researchers showed that varying degrees of friction between the fingers changes the elastic performance of the clip. And as a result, they have gained important insights that can be used to apply this advanced mechanism in all kinds of robotics.