### Science in a snap

This exercise is a part of Educator Guide: Camera Captures Physics in a Snap / View Guide

Directions for teachers: Ask students to read the online Science News article “New high-speed video reveals the physics of a finger snap,” which details scientists’ exploration of the friction required for finger snapping, and answer the following questions. A version of the article, “Camera captures physics in a snap,” appears in the December 18, 2021 & January 1, 2022 issue of Science News. If students read the version of the article that appears in print, have them skip question No. 2.

1. What is needed for a successful finger snap? Explain the physics of a finger snap.

Friction plus the compressibility of the finger pads are necessary for a successful finger snap. When the middle finger and thumb come together in a normal snap, the finger pads compress, increasing surface area and friction between them. That friction allows energy to be stored before it’s suddenly released.

2. What is the duration, rotational rate and acceleration of a finger snap? Why might the article’s author compare those measurements with a blinking eye and a baseball pitcher’s arm?

Finger snaps last about seven milliseconds. As the middle finger moves from the thumb to the palm, it rotates up to 7.8 degrees per millisecond and accelerates nearly three times as fast as a baseball pitcher’s arm. Comparing the measurements with those of a blinking eye and a pitcher’s arm gives readers a frame of reference to help them better comprehend the results.

3. What equipment did scientists use to study finger snapping, and what variables did they test?

Scientists used high-speed cameras and force sensors to study finger snaps under various conditions. The scientists studied bare snapping fingers, snapping fingers covered in lubricant and snapping fingers covered in rigid thimbles.

4. What did scientists learn from studying snapping fingers covered in lubricant?

Lubricated snaps were duds. That’s because the slick thumb and middle finger can’t produce enough friction, which means less stored energy and a slower snap.

5. What did scientists learn from studying snapping fingers covered in high-friction rubber?

High-friction snaps also were duds. That’s because the friction delays the fingers’ release, leading to a slower snap.

6. Based on the researchers’ findings, would Thanos — the villain in the movie Avengers: Infinity War — have been able to snap his fingers while wearing a metal glove? Explain.

No. A metal glove’s fingers would probably be too rigid to properly compress and create enough friction.