Researchers have finally revealed the complex process that generates sound under the hand claps, a discovery that shows how even simple actions can be rich in physics.
The research that was published in the journal Physical review researchshows that the distinctive “pop” sound of a flap is not only from two hands smashing into each other, but a much more complex phenomenon.
The key to generating sound from clap is a cavity in air that is compressed and pushed out of a small room.
Researchers followed a multidisciplinary approach to understanding claps using live experiments, theoretical modeling and silicon replicates of human hands.
They modified the volume and duration of flaps by changing the speed, the shape of the hands and even skin softness.
“We clap all the time, but we haven’t thought deeply about it. That’s the point of the study,” said co -author Yicong Fu of Cornell University, “to explain the world with deeper knowledge and understanding.”
“The point was not to look just at the acoustics or flow excitation or the collision dynamics, but to look at them all at the same time,” said Likun Zhang, another study author from the University of Mississippi. “It is an interdisciplinary effort that allows us to really understand how sound relates to towel.”
The study shows that when the hands gather under a flap, they create an air pocket between the palms. This pocket is quickly expelled from the narrow opening between the index finger and the thumb, causing the air molecules to vibrate.
Researchers compare this vibration with the Helmholtz resonance principle, which is behind the tone that was heard when blowing over the mouth of an empty bottle.
“Traditional Helmholtz resonators have stiff walls like the glass walls of a bottle. This produces a long-lasting sound that dampens very slowly because most of the energy contributes to the acoustic signal,” explained Dr. Zhang. “But when we have elastic walls – let’s say our hands – there will be more vibration of the solid material and all this movement absorbs energy away from the sound.”
This is why clapping generates a single card “pop” as opposed to a longer noise, researchers say.
Researchers hope their research can help inform music education, where hand flaps are often used for rhythm timing.
The study also shows that every person’s clap has a different sound and a different frequency, indicating that clapping can be used in the future as an identification method, such as how we use fingerprints.
“One of the most promising uses of this research is human identification. Just through the sound we could tell who has done it,” said Guoqin Liu, another author of the study.