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By Quantum Tunneling.
..... or the tip of a whip as it is cracked the sound that is heard is an expanding faster than a sound wave.
Yes, the bang that is heard is the whip at its very end exceeding the speed of sound and collapsing the waves around it. It is not the same as the sound that is heard by clapping our hands.
Quote from: Just thinking on 18/06/2021 23:48:49Yes, the bang that is heard is the whip at its very end exceeding the speed of sound and collapsing the waves around it. It is not the same as the sound that is heard by clapping our hands.Iím not sure what you mean by ďIt is not the same as the sound that is heard by clapping our hands.Ē the sound envelope and spectrum are different, but the cause is the same - something pushing air faster than the speed of sound.The pressure waves ahead of the whip tip (and the aircraft) are compressed not collapsed. If they collapsed there would be no sound. This compression causes a sharp increase in air pressure which is the sound we hear.Research (Neville Fletcher) shows that the sound of a handclap has the same cause. Air travelling at greater than the speed of sound as it tries to leave through the reducing gap between the hands creates a pressure (compression) wave, the only difference between this and the whipcrack being that this wave has a superimposed oscillation.The whipcrack again has a similar cause to the aircraft, that of the tip exceeding the speed of sound and compressing the air. The difference is that the whip produces a single pressure wave, whereas the aircraft produces 2, one at the nose (positive pressure) and one at the tail (negative pressure) which are far enough separated to allow them to be heard as distinct sounds. This doesnít happen with whip or handclap as the distance between leading and trailing edges are too small.
I thought that the sound of hand-clapping was just the sound that is made by objects colliding together
Quote from: Just thinking on 19/06/2021 15:43:49I thought that the sound of hand-clapping was just the sound that is made by objects colliding togetherIt's more complicated than that, but hand clapping is not a sonic boom, but it still makes far more noise than the same motion at the same speed with the back of your hand, which is more just the sound of the collision. The loud report is more akin to the noise made by popping bubble wrap.As for the whip, the crack only occurs when the tip moves at twice the speed of sound. It isn't the motion of the tip that causes the crack, but rather the motion of the loop that travels the length of the whip.
I thought that the sound of hand-clapping was just the sound that is made by objects colliding together is the bang of a car crash a supersonic bang I do not think so.
I would be interested to hear your version of why a thunder boom sometimes can last for a number of seconds and not just have one loud bang.
Quote from: Just thinking on 19/06/2021 15:43:49I thought that the sound of hand-clapping was just the sound that is made by objects colliding together is the bang of a car crash a supersonic bang I do not think so.As @Halc says, it is more complicated than that. Itís not the hands that break the sound barrier, as I said itís the escaping air.Fletcher* determined that for flat hands coming together over a 10ms period the transition of the escaping air from sub to supersonic occurred at 9.96ms, ie before the hands contacted each other. The majority of the sound comes from the shockwave, the soft tissue of the hands absorbs most of the physical contact sound.A car crash is a complex cacophony of sound. Although there will be some surfaces which trap air, it is mainly the fracture sounds we hear eg breaking glass, crumpling metal. So, I agree with you that a car crash is not a supersonic bang.You might be interested in this paper** on whip crack. It explains why the tip speed is 2x speed of sound, as @Halc mentioned, and shows some photos of the shockwave produced by the tip. He also describes the role played by the taper. You donít have to follow the maths if you donít want to as there are some good descriptions in the paper. https://www.researchgate.net/profile/Alain-Goriely/publication/243243782_Whip_waves/links/5e4c139492851c7f7f455cde/Whip-waves.pdf?origin=publication_detailQuote from: Just thinking on 19/06/2021 15:43:49 I would be interested to hear your version of why a thunder boom sometimes can last for a number of seconds and not just have one loud bang.Most people think of the thunder bang as coming from the lightning strike, but as you say, it comes from the heated air as the lightning passes through the air. Not only are there multiples strikes in what we see as one bolt, but the length of the bolt can be typically 2-3 miles with sound being generated from points all along the length which will reach us at different times. A lot of lightning is cloud to cloud rather than ground strike, so the degree of rumble you hear will depend on the orientation of the bolt relative to your position. The time of sound travel will also depend on temperature with higher, colder air giving slower times.* Neville Fletcher is an expert on the physics of sound production, famous for his work with Tom Rossing (Emeritus Professor of Acoustics) on the physics of musical instruments.** I wouldnít normally recommend ResearchGate as a fully reliable source (but it is better than Quora), however, Alain Goriely is a Professor of maths at Oxford so I have some confidence in his analysis which at first sight seems reasonable.By the way, I donít think anyone here is being picky, but it is important to be accurate.
I still believe
the harder we hit the louder the sound but no sonic boom only impact noise.
Quote from: Just thinking on 20/06/2021 11:48:31I still believe If this were a religion forum then your belief would count for something, but here we look for evidence.I know the research of Neville Fletcher, have read his papers and books, have discussed his work with him and used some of it in my own projects. It would help if you could provide us with details of research you have conducted in this area, papers you have presented to symposia etc, to give your assertions some credibility and allow us to see your methods and workings. If you truly think that science is a way of life then you need to start living it.Quote from: Just thinking on 20/06/2021 11:48:31the harder we hit the louder the sound but no sonic boom only impact noise. Your argument is fallacious.The intensity of a sound wave is related to the pressure variation; so, in the shockwave case, the faster the hands come together the greater the pressure of the expelled air hence the louder the sound. So your suggestion does not falsify the shockwave case.You talk of belief, perhaps you are a doubting Thomas who needs to feel (or hear) the hands.Letís think up a simple experiment. A loud handclap is typically produced by using, say, the closed fingers of the R hand and slapping them into the palm of the L hand, this produces the characteristic loud crack of the clap.So practice this as a regular, say 1/s, clap using the same speed and force until you consistently produce a series of loud claps. Now without changing the speed or force slightly spread the fingers of the R hand. You will notice that the loud crack disappears to be replaced by a soft flap. The speed is the same, the force is the same, the contact area is the same, all that has changed is that the air is no longer compressed and forced out through the edges of the hand forming a shockwave. You are left listening to the impact of the fingers only.Of course this does not prove that the air reaches supersonic, to do that you need the lab and equipment used by Neville. However, it does show that it is not just the impact of the fingers - itís more complicated.