[HN Gopher] The physics of hand clapping
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The physics of hand clapping
Author : RafelMri
Score : 71 points
Date : 2023-08-31 20:44 UTC (2 days ago)
(HTM) web link (physicsworld.com)
(TXT) w3m dump (physicsworld.com)
| nwoli wrote:
| One of the few articles you'd write and AI stock photos wouldn't
| be helpful
| [deleted]
| sublinear wrote:
| What's with all the fake science content lately trying to claim
| all sound is caused by sonic booms?
| misnome wrote:
| Interesting! Presumably you have a source backing up the claim
| that the article and paper it's based on are fake?
| havnagiggle wrote:
| Try this: do a small clap. Then do a big clap. Now slap the
| table, chair, or wall you are near. All of them are obviously
| not sonic booms. QED.
|
| You can make sonic booms with bull whips. They are quite a
| different sound than just slapping and clapping. Check them
| out on YouTube.
| misnome wrote:
| And a supersonic plane flying overhead doesn't sound like a
| bull whip. Therefore supersonic planes are a lie, QED.
| whatshisface wrote:
| Just because the thing you hit continues to vibrate and
| emit sound after it is struck, doesn't mean there wasn't a
| small sonic boom caused by the air escaping the contact
| surface.
| saberience wrote:
| You think a gentle clap is pushing air around at 343 meters
| per second?
| anon____ wrote:
| Well, not _around_. The sound of a clap is travelling
| _exactly_ with the speed of... sound. But not one bit
| faster, of course.
| misnome wrote:
| I dunno, unlike - apparently - you, I'm not an expert on
| the last few microseconds of the microfluidics of what
| happens to small volumes of air suddenly evacuated from a
| hand-sized area under constant compression.
|
| I take it that this means your source for refutation is
| "Lack of imagination"?
| [deleted]
| willis936 wrote:
| For one, I can't move any part of my body at supersonic
| speeds.
| misnome wrote:
| It's a good thing that's completely not what is being
| claimed then.
|
| I can't move any part of my body at the speed of sound, and
| yet - somehow - I still manage to produce vibrations that
| move at the speed of sound.
| willis936 wrote:
| It's a good thing that pushing air at the speed of sound
| is not how you make sonic booms. You need to physically
| move an object at a supersonic speed to make a sonic
| boom.
|
| So when you cast doubt on the claim that claps do not
| involve sonic booms you then have the burden of proof to
| demonstrate that a hand has supersonic motion. Please
| provide your argument and stop wasting time with
| pointless rhetoric.
| [deleted]
| cloudmike wrote:
| Finger snapping is fascinating too. I always assumed the sound
| happens when your finger rubs quickly against your thumb. But
| it's actually after that, when your finger strikes the fleshy
| part of your thumb. You can verify this by blocking your finger
| from striking your hand.
|
| So it's actually more like finger clapping. The "snap" part just
| lets you build energy for the "clap" part. Maybe obvious to some
| but I amazingly only learned this later in life.
| michelb wrote:
| I'm curious how finger snapping started. Someone must have been
| the first and thought it was useful. I can't remember when I
| learned it myself, i must have been very young when i was
| taught how to do it.
|
| Edit: and then there is Beshkan, which TIL.
| pluijzer wrote:
| Still doesn't explain the sound of one hand clapping.
| jojobas wrote:
| Half-sonic boom.
| [deleted]
| hobs wrote:
| I didn't get this was a koan until I realized that most people
| cant clap one handed.
| jhncls wrote:
| Well, in some countries, instead of clapping two hands,
| people clap on tables or armchairs.
| tim-fan wrote:
| > _As two flat hands collide, the air between them is forced out
| increasingly quickly, ultimately exceeding the speed of sound.
| This creates an abrupt pressure change, resulting in shock waves
| that make up a large part of the noise we hear_
|
| So the clap is a mini sonic boom between your hands?
| tgv wrote:
| That sounds surprising to me, too, because I can vary the
| loudness by moving one hand faster or slower towards the other.
| My intuition says that a sonic boom is a "catastrophic" event,
| so there should be a threshold. I'm wondering how they measured
| that.
| treyfitty wrote:
| The most interesting part of this statement is that you
| physically move both hands to clap... I let my dominant hand
| "hit" my other hand... is that not how everyone does it lol
| Sakos wrote:
| Look around sometime. I never see everybody clapping the
| same way. There are tons of variations, including what you
| do, and plenty of people use them.
| magicalhippo wrote:
| I mostly move both, but vary a bit depending on intensity
| and frequency. It's faster to clap against, but I get more
| sound moving both. It also spreads the effort, so I prefer
| it for low intensity clapping.
| adhesive_wombat wrote:
| I think you'll be ok, considering at least one person does
| this: https://twitter.com/MetroUK/status/748854767938473984
| dmbche wrote:
| The sonic boom comes from the object going faster than its own
| soundwave and crossing it, this just seems to be the product of
| a big pressure differential between the clap and ambiant air
| saberience wrote:
| I do not believe there is a literal "sonic boom" when clapping.
| It's possible to cap very slowly and still make a small noise
| and I don't believe my slow-clapping is pushing air around at
| 343 meters per second.
| whatshisface wrote:
| Why not? The size of the channel it has to move through goes
| to zero as your hands meet, but the volume reduction per
| second is roughly constant. That means the velocity goes to
| "infinity."
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