What Makes The Pop Sound When You Clap Your Hands? New Study Reveals

Clapping is an inherent human action performed to cheer, protest or pray, but a new study has shown that the gesture is as much a scientific event as it is a social one. Researchers from Cornell University and the University of Mississippi delved into the science behind clapping. The study, published in the journal Physical Review Research, shows that the sound of a clap is not just due to two hands smashing into each other but rather a much more complex phenomenon.

"This is the first time we have had a systematic study where we integrate physical experiments and theoretical modeling, and it's only possible because of the collaboration between our universities," said Likun Zhang, associate professor of physics and senior scientist at the National Center for Physical Acoustics.

"The point was not to look just at the acoustics, or the flow excitation or the collision dynamics, but to look at them all simultaneously. That's an interdisciplinary effort that allows us to really understand how sound relates to hand clapping."

While most people think that the sound of a clap comes from the hands hitting each other, scientists found that the noise comes from a cavity of air that is compressed and pushed out of a small space. The compressed air behaves like a Helmholtz resonator. This is the same principle behind blowing across a bottle's mouth. The palms create a cavity, and the gap near the thumb acts like a neck.

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Using powder tests and airflow analysis, the scientists confirmed that air escapes through the opening between the thumb and index finger. This air jet vibrates and creates sound waves.

The study findings showed a clear relationship between clap speed and volume. Faster claps compress the air more, creating stronger air jets and louder pops.

"We clap all the time, but we haven't thought deeply about it. That's the point of the study - to explain the world with deeper knowledge and understanding," said Yicong Fu, doctoral student at Cornell and lead author of the study.

The study also showed that each person's handclap is unique owing to the cavity shape, skin elasticity and rhythm. This may make it useful in identity recognition.