Name: Wildman Jackson
Status: Other
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Question:
I have heard that when you hear thunder, you can count seconds,
and every seven seconds represents a mile in distance of the storm from
yourself. Is this an accurate measurement? Has anyone actually calculated how
to tell how far a lightning bolt has struck from himself by counting seconds?
Replies:
If you assume that the lightning and thunder occur at the same
instant, then you can calculate distance by measuring the time that it takes
to hear the thunder. Just multiply time that it takes by the velocity of sound
in air and you will get the distance that the sound has traveled. (the
velocity of sound in dry air at 25 C is equal to 346.29 m/sec. However the
velocity will vary with humidity and temperature). Bon computite.
Woodford
This is true because of the laws of physics. The speed of light is
so fast that you see the lightning flash instantly (it only takes sunlight 8
minutes to travel all the way to Earth). But sound moves much slower. We know
the speed of sound (see last reply) so speed x time = distance. Sound travels
1 mile in about five seconds and one kilometer in three seconds. "Heat
lightning" is lightning from a thunderstorm that is so far away that the sound
never reaches your ears.
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