Finger snaps rely on huge angular accelerations, fake fossils on Mars

Physics

Have you ever thought about what happens when you snap your fingers? Raghav Acharya, Elio Challita, Mark Ilton and Saad Bhamla have looked deeply into the physics of the finger snap and published a paper about their surprising findings in the Journal of the Royal Society Interface.

Based at the Georgia Institute of Technology and Harvey Mudd College in the US, the quartet has discovered that the motion of your finger during a snap undergoes the highest angular acceleration that the human body is known to be capable of. They came to this conclusion by studying snapping fingers using high-speed imaging, automated image processing, and dynamic force sensors.

They found that a finger snap happens in about 7 ms, which is about one twentieth of the time its takes to blink an eye. The measured angular acceleration was 1.6 million degrees per second squared – which is about three times greater than the acceleration of the arm of a professional baseball pitcher. A pitcher, however, does develop a higher angular velocity than a finger snapper.

Latch and spring

When they are not snapping their fingers, the team studies mechanisms used by a range of living organisms to store energy and then quickly release it. They say that finger snapping is an example of a latch-mediated spring-actuated system, which is used by some termites and ants to make snapping noises with their mandibles. The team also looked at the role friction places in snapping by covering their fingers in various materials. When low-friction metal was used, the velocity of the finger dropped dramatically – illustrating the importance of friction in the snapping process. However, when high friction rubber was used, the velocity also dropped – suggesting that there is a “Goldilocks zone” of friction for snapping.

You can read more in “‘Oh, snap!’ A record-breaking motion at our fingertips

False fossils

We know about organisms that lived on Earth a very long time ago because occasionally one of those plants or animals was fossilized and preserved for posterity. Scientists believe that Mars may have supported life several billion years ago, so looking for fossils on Mars seems like a reasonable thing to do. But what would Martian fossils look like and how could we tell them apart from structures in rock that were formed by non-living processes?

In the UK, Julie Cosmidis at the University of Oxford and Sean McMahon at the University of Edinburgh have done a review of non-biological geochemical processes that can create structures that look a lot like fossilized microbes. Writing in the Journal of the Geological Society, they identify dozens of processes and say that there could be many more.

These processes can create deposits that look like bacterial cells as well as carbon-based molecules that closely resemble the building blocks of life (see figure).

“We have been fooled by life-mimicking processes in the past,” says Cosmidis. “On many occasions, objects that looked like fossil microbes were described in ancient rocks on Earth and even in meteorites from Mars, but after deeper examination they turned out to have non-biological origins.”

McMahon adds, “For every type of fossil out there, there is at least one non-biological process that creates very similar things, so there is a real need to improve our understanding of how these form”.

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