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The Thunder Mystery
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Which comes first, thunder or lightning? Like the chicken
first or egg first puzzle, this is a question that still sends
many into rumination. All we need to remember is that light
travels faster than sound and therefore there is no doubting
the fact that thunder comes after lightning.
Thunder is the explosive sound produced by an ordinary
lightning discharge. When there is a bolt of lightning, it
heats the air around it so quickly (within a few millionths of
a second) and to such a high temperature (about 10,000° C, or
about 18,000° F) that the air molecules are pushed apart with
great force, much like in an explosion. A wave of compressed
air (a sound wave) moves out from the lightning bolt. |
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Interestingly, although a lightning strike seems to be over very
quickly, thunder can last much longer, changing in pitch and
loudness. This happens due to several reasons. Firstly, the
lightning bolt has an irregular shape and the lightning bolts
overlap. The air expands in all directions at once and objects on
the ground interfere with the sound. Because the lightning bolt is
not straight and is at an angle to the vertical, not all parts of
the bolt are the same distance from the listener. Therefore, sound
from different places on the bolt reaches the listener at slightly
different times. Also, sound from the far side of the lightning
reaches the listener after sound from the near side has reached him.
Since lightning often occurs in groups of several bolts very close
to each other, sound waves from different bolts mix to form a
continuous sound. The trailing rumbling effect are echoes from hills
or other reflecting objects. |
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How to calculate the distance between the
thunder and a listener
As we already know, sound travels slower than light and therefore
thunder is heard after the lightning is seen. The distance between
an observer and the lightning bolt can be estimated by counting the
number of seconds between the lightning and the thunder. The light
reaches the observer almost instantaneously, but the sound travels
at about 1.6 kilometers or one mile every five seconds. Thunder can
seldom be heard from more than a distance of twenty four kilometers
or fifteen miles.
At
any given time, there are about one thousand eight hundred
thunder storms raging at different parts of the world, generating
nearly six thousand flashes of lightning between them.
An interesting
incident occurred in Germany in the year 1930. Five glider pilots
baled out into a thunder cloud over the Rohn Mountains. They were
apparently trapped in thermal currents in large clouds, with speeds
of hundreds kilometers an hour. Thermal currents with such high
speeds could be devastatingly dangerous. Of the five pilots, only
one survived the drop. The other four were held aloft by the
thermals and they became entombed in ice. They must have looked like
giant hailstones. It was a while before the clouds finally released
them. |
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