We all know that thunder is caused when lightning superheats air causing it to expand violently (or something to that effect). But lightning is such a short-lived event, shouldn’t thunder be equally short? I would expect to hear a quick, sharp clap, but instead it’s usually a long roll. What’s the reason for this?
The only thing I can thing of is that the sound wave is being broken up by buildings, trees, etc. and thus reaching the listener in fragments.
I can think of two reasons.
The obvious one is that the original ‘CRACK!’ sound is echoing across the landscape.
The second is that the bolt of lightning is significantly long. Let’s say a bolt of lightning travels down 3000 feet from the clouds to a point a few yards away from you. You will hear the sound from the superheated air where the lightning bolt strikes almost immediately. The sound created at the top of the bolt will take longer to get to you, and by then it will be distorted by all the air it had to travel through to get to you.
Adding to the question, the initial crack consists largely of high-frequency tones, where the later rolling is mostly bass frequencies.
Badtz Maru, if it were just a question of distance travelled, one would expect that closer components would contain both bass and treble, while father, distorted ones might contain only bass frequencies. But this is not the case. I’m not saying your wrong, maybe my supposition is. But if so, could you explain why? Anyone?
This is kind of hard to describe without diagrams - let’s see if this works:
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OK. The diagonal line is the lightning. Lightning can go either from the ground to sky or from the sky to the ground. Let’s say the above strike is from the sky to the ground. Then the thunder from the top will reach you before the thunder from the bottom, and you hear a drawn-out rumble. OTOH, if it goes from the ground to the sky, the sound from the bottom has more distance to cover but is created first, so the sound all hits you more or less at once, and you hear a sharp, loud, clap.
I have no idea you true this is, but that’s what I heard and it seems to make sense to me.
I like the sound (no pun intended) of the length of the bolt having something to do with it. As for distance, I do notice that bolts that are really close (say within 1/2 mile of you) seem to have loud thunder that is shorter in duration, which would support the theory that it takes different amounts of time for the different frequencies to reach you. I forgot that these sounds we’re talking about are usually created quite some distance away from the observer, so it’s plausible that different frequencies could arrive at different times. Does anyone know how much of a difference in speed there is between high and low frequencies when travelling through air?
…however, I’m wondering if there are any more opinions/facts on this phenomenon.
Today, as I stood outside my office, I saw lightning that seemed to be some miles east of my position, yet the thunder sounded like it was rolling around directly above me. I waited for the next strike and paid closer attention. The thunder started soft and quickly grew to a loud clap followed by the rolling effect and ending with lower frequency rumbling. Again, the sound seemed to move around in the sky above me instead of coming directly from the east. Is there some kind of Dopler Effect taking place as the sound waves move through the sky? Why did the sound build, instead of beginning with a loud clap? The whole thing reminds me of an F-14 flying by at an airshow.
Here is a simplified explanation…
http://www.eecs.umich.edu/mathscience/funexperiments/agesubject/lessons/beakman/thunder.html
hmmm…one more time…
http://www.eecs.umich.edu/mathscience/funexperiments/agesubject/lessons/beakman/thunder.html
Mods…is there a problem in the automatic linking?
Hmm…not sure why that wouldn’t work, Reeder. Let’s try this.
Not only does lightning have a significant length there can also be many lightning strikes down the same path within a short time. Next time you see lightning you may notice that it doesn’t always just flash once, sometimes there are 2 or 3 flashes of the same bolt. Each of these flashes creates its own thunder.
The further away it is, the more chance you get of hearing the thunder from various diferent locations as it echoes off mountains, buildings, or whatever. If it’s close you’re hearing more of the direct sound and less of the ambient reverbed sound. Also close thunder has a sharper “crack” compared to distant thunder where the higher frequencies are attenuated below audible levels long before the sound reaches you.
I used to live by a lake surrounded by mountains and when there was a thunder storm the thunder would roll continuously as the echoes would go on until the next lightning strike.
[list][list][list][list][list][list][list]LIGHTNING BALL?
[LIST]…:eek:…