Chopsticks are not third-class levers #VeritasiumContest
Channel: Marcosticks
Date: 2021-07-07

This is a short episode that explains the counterintuitive finger dynamics involved in using chopsticks. No one has bothered to study the biomechanics of chopsticking in these thousands of years. People and even researchers simply assume that chopsticks are 3rd-class Archimedean levers. The famous "How to Use Chopsticks Like Mr. Miyagi" illustration asserts the same misconception. But... visual similarities between a hand holding a pair of chopsticks, and a 3rd-class lever is just... a superficial resemblance. A lever is not a static picture. A lever is pushed to do work. When one actually observes a hand moving chopsticks in slow motion, a different story unfolds.

It turns out that the motion of a planetary gear train more accurately describes how fingers grip and roll the top chopstick. The top chopstick is wedged between the thumb, the index finger and the middle finger, as an extension of these three fingers. The top chopstick becomes a cantilever sun gear, snugly surrounded and rolled by these three fingers. 

It's just that no one bothered to look into this matter before, in thousands of years.

If this video piques your interest in this topic, head over to https://marcosticks.org/planetary-gears where we explain in details the physics of chopsticks.

0:00 - Intro
0:06 - Standard Chopstick Grip
0:14 - WRONG: chopsticks == 3rd-class lever with a fixed fulcrum
0:23 - WRONG: thumb pad serves as a fixed fulcrum
0:30 - Top chopstick becomes a cantilever extension of three fingers
0:39 - Your fingers make an air quote, pulled by tendons and muscles via 3rd-class leverage
0:51 - The top chopstick is a cantilever sun gear, surrounded and rolled by three fingers

For more information on chopsticks, go to https://marcosticks.org/. Or continue watching here, the first episode of "Ten thousand ways to use chopsticks", on the Standard Grip: https://youtu.be/VQ8HGQxHQ-I.

At 0:06, chopsticks are shown compressing a sponge. There is nothing extraordinary about this everyday use of chopsticks. But a lesser-known use of chopsticks is shown at 0:51 - chopsticks are used to stretch a rubber band. These two operations, the compression and the extension, comprise what we call the litmus test for chopstick grips. Slow motion footages of compression and extension can be seen here: https://youtu.be/FFWZNHTxTcE.

This short 1-minute video is our first entry into the Veritasium Science Communication contest (#VeritasiumContest). We have a second entry as well: "What chopstick team is your TWICE idol on, again?" https://youtu.be/EhyfUKqsZCU. Details of the contest can be found here: https://www.veritasium.com/contest.

Music used with permission. All illustrations are from marcosticks.org, except for a few: textbok lever from Simple Machines prezi.com, thumb as fulcrum from Chen S.W. et al – Kinematics Analysis of Chopsticks Manipulation (fulcrum and effort labels are added for illustration per description from the paper), arm as 3rd-class lever from Kinetic Anatomy w/web resources us.humankinetics.com, and finger tendons as 3rd-class levers and pulleys from Neumann, D. A. (2002). Kinesiology of the Musculoskeletal System.

#HowToUseChopsticks #StandardGrip #Marcosticks #VeritasiumContest #biomechanics #ergonomics