Dr Michelle Dickinson: nanotechnologist explains where the science of clapping comes from

Most of us think clapping is just about two hands hitting each other, but new research out this week in the journal Physical Review Research found that the clap that we hear actually comes from the air being squeezed out between our palms.    

When your hands come together, whether flat or cupped, they trap a tiny bubble of air. That bubble escapes through small gaps, like the one between your thumb and index finger, creating a mini jet of air that blasts out and disturbs the surrounding atmosphere. 

This results in a burst of sound created by a phenomenon called Helmholtz resonance, the same thing that happens when you blow across the top of a bottle. Your hands, in that moment, are transformed into a musical instrument. 

To test their theory, the research team built silicone hands of different shapes and stiffness levels, and gave them microphones, pressure sensors, and high-speed cameras. They clapped the hands together again and again, studying every tiny movement and sound wave. 

They found that the shape of your hands plays a big role in how your clap sounds. Cupped hands trap more air and make a lower, deeper sound. Flat hands create a higher-pitched pop. Even the grooves between your fingers contribute, acting like tiny open-ended pipes that add extra tones. 

The study showed how a handclap might actually be used to identify someone. Because everyone has differently sized hands, skin textures, and clapping styles, no two claps are exactly alike, each person’s clap is unique, like a musical fingerprint. 

One researcher is already exploring whether clapping could be used to take attendance in classrooms - where students walk into a room, clap once and the system recognises you and checks you in. 

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Episode Transcript

Speaker 1 (00:06):
You're listening to the Sunday Session podcast with Francesca Rudgin
from News Talks EDB.

Speaker 2 (00:12):
Doctor Michelle Dickinson joins me now with her science study
of the weekenders. I was just saying before the break, Michelle,
at the Radio Awards, we were all waking our hands
together trying to make the biggest sound we possibly could
to support our colleagues and things. And it turns out
we could have been creeping quite differently and having just
as good an impact giving the message across. This is
so interesting.

Speaker 3 (00:33):
Did you know It's not often that I, because I
read all these research papers forew so I have something
on Saturday. It's not often that I'm like, I did
not know that.

Speaker 2 (00:40):
No, I had no idea.

Speaker 3 (00:42):
But here we go. Okay, So this is from the
journal Physical Review Research. It's open source. You can go
read it. It's full of maths. Sorry, so you might
just want to look at some of the pictures if
that's not your deal on a Sunday morning. But basically
it says that the sound of clapping is not from
our hands hitting each other, which we would assume, of course,
it's actually the sound of air being forced out between

(01:04):
our palms and I'm like, and then it got into
it and it's so exciting. Okay, I get excited about this.
I'm in it. So when our hands come together in
a clap, they trap a tiny bubble of air, and
that tiny bubble of air has to escape somewhere through
the small gaps in wherever our hands have it between
our fingertips. Usually it's between our thumb and our index finger,

(01:25):
and that creates a jet of air that blasts out
and disturbs the surrounding atmosphere, which results in a burst
of sound created by a phenomenon. And you'll know this phenomenon,
maybe not by name, a phenomenon known as the Helmholtz resonance.
If you have ever and it's usually with a beer bottle. Sorry,
if you have ever blown into a beer bottle over

(01:46):
the top of it and it makes that sound, it's
the same thing. So that forcing of the air through
a narrow channel either means that you can play Twinkle
Twinkle a little Star on your beer bottle in the bar,
which many of us have done, or it's also creating
a sound that is the sound of clapping. So this
is what I love about the study. First of all,

(02:06):
how do they do this? They got ten people aged
between eighteen and seventy to clap three different types of clap.
Apparently there's the cupped clap this well, yeah, there's the
palm to palm clap piece, and then there's the palm
to finger clap.

Speaker 2 (02:20):
The golf clippers. I call that nice.

Speaker 1 (02:22):
Yeah.

Speaker 3 (02:22):
And then they did high speed cameras microphones measured sort
of what that looked like. And then they three D
printed these fake hens out of the silicon. And then
they got these fake hens that are made out of
different shapes and different stiffnesses of the silicon to basically
clap thousands of thousands of times. And they set up

(02:43):
pressure sensors in them, high speed cameras and microphones to
measure literally every clap possible with these fake hands and
how they sounded and what they thought the sound was
coming from. And then they took baby powder. This is
why I love the study. It's so random. They took
baby powder and they sprinkled it into these fake hands
so they could watch where the Jetta air was coming
out of. Very sensible and so if you this paper,

(03:06):
ignore the mess. It's a lot, but look at the
pictures of these jets of air with this baby powder,
and it's really interesting. Well I found it interesting anyway.
So after all of this, they figured out that it's
not the sound is not from the slapping of the
hens together, it's from these tiny jets of air, and
they're able to measure the jets and look at how
the air was disturbed, and sound is just vibration, which

(03:28):
is air being disturbed, and that's what they found. And
they found that cup hands trap more air, which makes sense,
which gives you a lower and a deeper sound, and
that flat hands give you a high pitched pop. And
there you go. What they found too from doing this
is that so even even the flat hen where you
feel like there's only a little bit of air that

(03:48):
can get trapped in there, there is still the air
coming out, still the air coming out. And then they
found that everybody's clap is personal to them, so we
have our own clap fingerprint. Nobody claps like you, Francesca,
and they could identify you in a room, maybe at
the radio wards from your clapping because only you clapped
like you. Because it's based on the grooves of your
finger and your fingerprints and everything to do with just you,

(04:10):
and then they went down this rabbit hole of well,
maybe we could have like a school attendance system where
kids just clapped when they came in and we could
work out the school anyway. It got a little bit bizarre,
but it's an offer paper Joeneral, Physical review research, lots
of mass ignore that. Look at the pictures. It's kind
of fun. Yeah, how do we clip?

Speaker 2 (04:27):
I love it very loudly and without a huge amount
of technique to it, and it's like it would be
my answer, Michelle, Thank you so much.

Speaker 1 (04:36):
For more from the Sunday session with Francesca Rudken, listen
live to News Talks it'd be from nine am Sunday,
or follow the podcast on iHeartRadio.