Nate Holt's Blog

July 5, 2009

Why does Thunder thunder longer than lightning lights?

Filed under: Musings — nateholt @ 9:28 am

(note: this originally appeared in July 2006 on the old blog)

I think a recent lightning strike took out my home air conditioning system. The repairman will be here tomorrow. I pretty much have to replace the whole system due to the need to flip over to the new ozone-friendly refrigerant. Talking $$$.

Of course this triggers some thinking about lightning. For example, a lightning stroke lasts just a split second, the whole thing stretching a couple miles up into the sky. The superheated air around the lightning stroke “explodes” and causes a sound spike, i.e. thunder.

So, if this thing lasts a split second, why doesn’t thunder just last a split second. I know, I know, in school they said it was just echoing off of hills, trees, buildings and stuff. But I don’t buy it. Here’s what I think (see crude AutoCAD drawing below… hey, I’m electrical, I can draw the lightning okay but that’s about it):


This sketch shows me standing a mile away from a 2.5 mile long lightning stroke. Flash! … wait 5 seconds, and I hear thunder (speed of sound is about 5 seconds per mile). But I don’t here “all” of the thunder right away. I just hear the part of it that was the closest to me, segments A and B. Both segments are about the same distance from my ear so this part generates a big, sudden “boom”. Then, over the next 2.5 seconds, the sound made by the lightning along segment C reaches my ear. Then, a second “boom” as the thunder created along the whole length of segment D reaches my ear at about the same time. And to finish it off, the thunder created by segments E and F reach my ear over the final 5 seconds of the thunder’s life.

Does this make sense? It seems more logical than the “echo off of buildings and trees and stuff” theory.


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