Clapping Hands

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Black and white video showing human hands clapping in a "cupped palms" configuration. Baby powder jets out from the space between the lower hand's forefinger and thumb.

Black and white video showing human hands clapping in a "palm-to-palm" configuration. Baby powder jets out from the space between the forefingers and thumbs.

Black and white video showing human hands clapping in a "fingers-to-palm" configuration. Baby powder jets out from the space between the lower hand's forefinger and thumb.

Although often associated with applause, hand clapping is more universal than that. The distinctive sound can mark rhythms, draw attention, and even test the surrounding acoustics. But how exactly does hand clapping work? A recent study shows that the acoustics of hand clapping come from more than just the collision of hands. Especially in a cupped configuration, clapping hands act like a Helmholtz resonator (think blowing across a bottle top), producing a resonant jet that squeezes out between the forefinger and thumb of the impacted hand. Check out the images above to see how that jet appears in various clapping configurations. (Image and research credit: Y. Fu et al.; via Physics Today)