New research work published in Physical Review Research,  elucidates the complex physical mechanisms and fluid dynamics involved in a handclap, with potential applications in bioacoustics and personal identification, whereby a handclap could be used to identify someone.

The researchers used high-speed cameras to track the hand motion, air flow and sound of 10 volunteers clapping, measuring the different frequencies when the size and shape of the cavity between hands changes: when clapping with cupped hands, flat hands or fingers to palm. They found the larger the cavity between palms, the lower the frequency of the clap, with the hands acting as a resonator—whereby the sound comes from the force of air through the hand's cavity and the opening between the thumb and index finger.

It's the air column pushed by this jet flow of air coming out of the hand cavity that causes the disturbance in the air, and that's the sound we hear.

The researchers compared the human data to that produced with simplified replicas, as well as theoretical projections of how air would move through a traditional resonator, called a Helmholtz resonator.

They confirmed both experimentally and computationally that the Helmholtz resonator can predict the frequency of the human handclap.

It's a confirmation of this unifying principle that may be helpful in other fields, especially bioacoustics, because that principle may help explain all kinds of bioacoustics phenomena, especially those involving soft material collision and jet flow.

Additionally, the researchers studied why claps are so short, compared to sound made through a traditional resonator, finding that the softness of the hands plays a role: the soft tissues of the hands vibrate after impact, absorbing energy and dampening the sound.

When there's more vibration in the material, the sound attenuates much more quickly. So, if you want to get the attention of another person very far from you, and you want the sound to last longer, you might want to choose a certain type of handclapping shape that makes your hand more rigid.

The research further opens the door to the idea of using a handclap as a personal identifier or signature.

The handclap is actually a very characteristic thing, because we have different sizes of hand, techniques, different skin textures and softness—that all results in different sound performances. Now that we understand the physics of it, we can use the sound to identify the person.

Yicong Fu et al, Revealing the sound, flow excitation, and collision dynamics of human handclaps, Physical Review Research (2025). DOI: 10.1103/PhysRevResearch.7.013259