Thursday, 12 July 2012

Why does thunder sometimes sound like a sharp crack, and sometimes like a low rumble?


It depends on how far you are from the lightning. The closer you are, the higher the pitch of the sound you hear; the farther away you are, the lower the rumble.
First, we have to remind ourselves of what thunder is.
A stroke of lightning is extremely fast; it occurs with what might be called lightning speed. Its sudden heat makes the surrounding air white hot—heated to tens of thousands of degrees. The air expands at tremendous speed, after which it rapidly cools and contracts back to its normal temperature and pressure. Air moving so suddenly makes huge vibrations, and that's what sound waves are: shudders, or pressure waves, moving through the air. Hence, the noise of thunder.
It will not surprise you to learn that thunder travels at the speed of sound. But light travels almost a million times as fast as sound. Obviously,then, you're going to see the lightning flash almost instantaneously, but you won't hear the thunder until it travels from the lightning strike to your ears.

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