On 2/8/13 12:31 PM, Mark X2 wrote:
Hi Paul, Actually, it isn't the air expanding because of the heat that makes the thunder. The shockwave is caused by the rapidly imploding vacuum that is left behind when the spark disappears. It's comparable to cracking your knuckels or cavitation in a radiator.
Not really.. that "collapsing vacuum" explanation (which has also been used for thunder from lightning) is incorrect (and probably dates from the nature abohrs a vacuum days)
it *is* the rapid expansion that propagates the sound wave out. the heating is *much* faster than the cooling. Cooling has to proceed by conduction or radiation and is quite slow. Heating can occur very quickly,and the expansion can easily exceed the speed of sound in the surrounding medium.
"bumping" in a boiling liquid (as well as sonoluminescence) is from collapsing bubbles.
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