| Lightning - did I hear it twice?
Posted: 9/5/2009 10:53:38 AM | It's been a while, but at some time in the past, I remember watching lightning and thinking that I heard a low crackling as I watched it strike, even at a distance. The loud bang happened some time afterwards and I pretty much dismissed the idea that I heard 2 sounds, yet never understood what I (imagined?) I heard.
The other day, I was watching workmen driving piles on a construction site about a quarter of a mile away. Once again, I heard (and felt) a crack at the instant I saw the hammer hit the piling then a louder bang about one second later. It was then that I realized the velocity of sound in water is about 5 times the velocity in air and in rock more than 20 times higher, so I must be first hearing the sound conducted through the ground, followed by the sound conducted throught the air.
I wonder if this explains my perception that I heard lightning as it struck in addition to the bang some time later. Has anyone else noticed this? | |
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| Lightning - did I hear it twice?
Posted: 9/5/2009 11:22:58 AM | Quietjohn
I"m only conjecturing, but there's also the possibility that you were hearing a "continuation" of the whole process -- in the case of lightning, the "slicing" of the atmosphere first, and the "implosion" of the atmosphere as it went back to stasis. In the case of the hammer, you might have heard the first contact of metal to rock, followed by the actual harder impacting of both surfaces.
Reckon I'll have to go out to Dollar General and buy me a jack hammer, and have my 12 year old daughter go out a distance and "git er done" while I sit back drinking my coffee listening for the sound effects. I'll let you know.
Alternatively, maybe we have some acoustical engineers here on POF that can let us know.
BTW, nice to see ya in the forums agin. | |
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| Lightning - did I hear it twice?
Posted: 9/5/2009 11:39:39 AM | The lightning, yes. A prolonged bolt in which I could hear a crackling/buzzing noise followed at the conclusion by a loud bang. It's conjecture on my part but I believe that the crackling is the sound of the discharge and the bang is the concussive "clap" of the air when the bolt concludes.
If you've ever seen those lightning generators in real life or on television, you hear a buzzing or crackling from the discharge and a clap at the end. Same thing.
Very cool, though. I love thunderstorms. Even big nasty ones like that which hit us in Ontario a few weeks back. | |
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| Lightning - did I hear it twice?
Posted: 9/5/2009 12:18:17 PM | Thanks Krebby - and both of you for the responses.
Presumably any sound which originated from the lightning would take the same time to reach our ears, so the crackling shouldn't arrive first - and certainly not almost simultaneously with the visual flash. The only thing that makes sense to me is that the impact of lightning with the ground creates a sound which travels through the earth at around 6,000 meters per second and therefore reaches me much earlier than the sound traveling through air at about 300 meters per second.
I don't recall hearing the crackling with high altitude (cloud-to-cloud) lightning.
Yes, stargazer, I think thunderstorma are really cool, too. Another of those magical things that nature does to astound us. I'm living in the tropics now, bracing for the stormiest part of the year. Some of the storms light up the sky constantly for as much as a couple of hours and sometimes you can even smell the ozone in the air. If only we could harness all that energy? But it's a spectacular show anyway - and compared to my native England, the rain is mercifully warm! | |
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| Lightning - did I hear it twice?
Posted: 9/5/2009 1:47:45 PM | The crackling would occur first if it was a preceding event. The crackling of the earth would be the lightning bolt streaking through the atmosphere, charging particles as it proceeded (sorta like the sound you hear on the old frankenstein movies ,I love Frankenstein movies but my favorite is "The Wolfman" with Cheney as the wolfman, but I digress) as the electricity "does its thing." The second sound is a follow-up event, the atmosphere making a "clapping" sound because the space disturbed by the lightning bolt is quickly moving back to its original state -- an implosion of air.
Throw a huge boulder into a lake sometime -- first sound, the clap of the boulder hitting the surface of the water, followed by a gurgling"whump" as the water, separated by the boulder as it sunk below the surface, is now coming back to fill the void created by the boulder as it passed through the body of water.
The foregoing is based on scientific evidence. I took my 12 year old daughter out by the lake and proceeded to drop her from shoulder level. We did this 3 times, she gleefully wanted to proceed with the "experiment" but my body grew weak from the exertion. Therefore the sample is at present inadequate. We will proceed with this experiment 27 more times, to reach the level of statistical significance made mandatory by the "central tendencies theorem. She is getting ready for the experiment by eating hot dogs, which will no doubt create a bigger mass, and create better sound quality appropo of the following formula:
E = MC(squared).
The above is still based on conjecture, and not on sound theoretical principles of physics, albeit some experimentation was done, however inadequate, but fun.
Your results may vary.
Postscript: You may not have heard the crackling from cloud to cloud lightning due to directional sound travel.
Advisory: The experiment was done by professional stuntpeople; do not attempt this at home. | |
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| Lightning - did I hear it twice?
Posted: 9/5/2009 2:50:36 PM | 'quietjohn2'..//sometimes you can even smell the ozone in the air//
Hmm.... Yep.... Wow... What a great sentance :D
I'm jelous of your tropical adventures. | |
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| Lightning - did I hear it twice?
Posted: 9/5/2009 6:10:20 PM | | The suggestions so far fit, but I'd add that if by "some time afterwards" you meant a week or more, then it could well be the second sound was unrelated to the first, and only seemed that way because it jogged your memory. I'm sure you would have considered this already, unless you won't until next week. | |
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| Lightning - did I hear it twice?
Posted: 9/6/2009 9:31:53 AM | I would suspect in both cases of lightning and pile driver sounds what you could be hearing is an echo from a temperature inversion above. In effect, it is an echo from the temperature boundary above.
In space launch missions, one reason for delays they don't often discuss with the public is concerning weather when there is a significant temperature inversion. The magnitude of blast damage from an explosion on the ground is greatly increased thus endangering nearby communities. The temperature inversion contains or reflects the shock wave making it stay at ground level instead of dissipating upward. The same thing can happen with any shock wave including sounds of lightning or pile drivers. The reason its not mentioned is basic PR. NASA doesn't like to remind the tax paying public that their toys could blow up. | |
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| Lightning - did I hear it twice?
Posted: 9/6/2009 9:53:40 AM | | Perhaps the two sounds were the sound of lightning being generated and the sound of lightning actually striking. I don't think I've ever been close enough to lightning to actually hear it hit the ground but if I was, I wouldn't be surprised if I heard two sounds. | |
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