If I see a lightning I must wait many seconds to hear the thunder because of the different velocity of light and sound in the air. This is true, I think. But why thunders lasts 1-2 second and the lightning only milliseconds? I've thought that this thing is given by the length of it: Maybe the noise of the thunder arrive from all the point of the lightning and so the noise that arrive from the top arrive later then the bottom one. But really I don't know. Thank you for your answers
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When you hear thunder that booms and rolls or crackles for periods of up to 10 seconds seconds, what you’re hearing is actually the shockwave from the entire length of the lighting bolt from the ground to the original sound source up in the clouds, which is expanding at high speed. You hear the blast of air closest to the surface, and the roll of the thunder then fades as shockwaves from higher and higher up the bolt reach your ears.
With lighting there is a single flash from the spark of lighting, and then it's over.
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Consider the horizontal distance travelled by a lightning bolt. If it hits a tree in your neighborhood you might hear thunder very soon. And if it started from a cloud 3 miles or so away, then you might hear thunder all the while you count to ten. Further, if that bolt zig-zagged with segments with all points almost equidistant from you, sharp cracking sounds might be sprinkled in with the main boom.
