### Science on screen

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” and watch a video interview with a scientist that did the research. Then, direct students to answer the first set of questions with a partner. Students should answer the second set of questions alone before discussing their answers with a partner. If time and resources allow, encourage students to try the demo they choose in the final question. A version of the Science News article, “Camera captures physics in a snap,” appears in the December 18, 2021 & January 1, 2022 issue.

Want to make it a virtual lesson? Post the online Science News article and video link to your virtual classroom. Discuss the article and questions with your class on your virtual platform.

Sounding off on a snap

1. Explain the physics behind snapping your fingers to create a sound.

When preparing to snap, fingers bend and finger pads compress, creating surface area between the pads that increases friction. The friction between bare fingers stores energy that is released all at once to accelerate the middle finger. The middle finger hits the palm at a high velocity, sending out shock waves that make the “snap” sound.

2. How does friction impact a finger snap?

If there is too little friction between the thumb and middle finger, not enough energy is stored between them. That means the middle finger can’t accelerate to the velocity needed to impact the palm with enough force to create a sound. If there is too much friction between the fingers, too much energy builds up, delaying the middle finger’s release and slowing acceleration.

3. List conditions that make finger snaps fall flat. Explain why snaps don’t make much sound under such conditions.

If the fingers are too rigid (like they could be in a tight glove) or too slippery (like they could be when covered in soap or some other lubricant), they may not be able to compress enough to create the amount of friction needed for an audible snap.

4. What popular film inspired the study described in the article? What procedure did the researchers follow to assess the scientific accuracy of a scene in the film? Is the scene scientifically accurate? Explain.

Scientists were inspired by a scene in the film Avengers: Infinity War in which the villain Thanos wipes out half of all life in the universe by snapping his fingers while wearing a supernatural metal glove. To test whether snapping fingers that are covered in metal is possible, the scientists first determined the conditions required to generate a normal finger snap using high-speed cameras and force sensors. Then scientists tried to mimic Thanos’ snap in the film by observing snapping fingers covered by rigid thimbles. Coupled with the newfound understanding of the necessity of finger compressibility and friction to generate a snap, the scientists determined that the scene is not scientifically accurate — Thanos’ gloved hand would not have produced an audible snap.

5. How would the scene have to be adjusted to be scientifically accurate?

The glove’s metal would likely have to be compressible and not too slick to create the friction needed to create a snapping sound.

Fact or fiction?

1. Think of a scene in a movie or TV show that features a scientific concept you learned this semester. Using your scientific knowledge, discuss whether or not the scene is scientifically accurate.

Student answers will vary. Students might analyze another scene in Avengers: Infinity War, a scene from a disaster movie or the scene from the movie Up in which helium-filled balloons lift and carry a house.

2. If the scene is not scientifically accurate or not as accurate as it could be, what conditions or adjustments could make it so? Explain.

Student answers will vary. Students should explore whether or not conditions other than those depicted on-screen could produce the observed phenomenon.

3. There are many online videos of science demonstrations, and some may show outcomes that cannot be reproduced. Find a video of a science demonstration that you would be interested in re-creating. Name scientific principles and concepts you would need to know to verify whether or not the outcome of the demonstration is scientifically possible. What conditions would have to exist for the outcome shown in the video to occur?