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.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_detail
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.