Thunder
is the sound made by lightning. Depending on the nature of the lightning and distance of the listener, it can range from a sharp, loud crack to a long, low rumble (brontide). The sudden increase in pressure and temperature from lightning produces rapid expansion of the air surrounding and within a bolt of lightning. In turn, this expansion of air creates a sonic shock wave which produces the sound of thunder.
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THUNDER TICKETS
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Cause
The cause of thunder has been the subject of centuries of speculation and scientific
inquiry. The first recorded theory is attributed to the Greek philosopher
Aristotle in the third century BC, and an early speculation was that it was caused by the collision of
clouds. Subsequently, numerous other theories have been proposed. By the mid-19th century, the accepted theory was that lightning produced a
vacuum. In the 20th century a consensus evolved that thunder must begin with a
shock wave in the air due to the sudden thermal expansion of the
plasma in the lightning channel. In a fraction of a second the air is heated to a temperature approaching 28,000
°C (50,000
°F)
[1]. This heating causes it to expand outward, plowing into the surrounding cooler air at a speed faster than sound would travel in that cooler air. The outward-moving pulse that results is a shock wave,
[2]
similar in principle to the shock wave formed by an
explosion, or at the front of a
supersonic aircraft.
More recently, this consensus has been eroded by the observation that measured
overpressures in simulated lightning are greater than what could be achieved by the amount of heating found. Alternative proposals rely on
electrodynamic effects of the massive current acting on the plasma in the bolt of lightning.
[3]
Etymology
The
d
in Modern English
thunder
(from earlier
Old English þunor
) is
epenthetic, and is now found as well in Modern Dutch
donder
, , (cp
Middle Dutch donre
, and
Old Norse þorr
,
Old Frisian þuner
,
Old High German donar
descended from
Proto-Germanic *
þunraz
). In
Latin the term was
tonare
"to thunder" (see also
tornado). The name of the Germanic god
Thor comes from the
Old Norse word for thunder.
The shared
Proto-Indo-European root is
*tón-r?
or
*tar-
, also found Gaulish
Taranis
and Hittite
Tarhunt
.
See also
Thursday (
Old English Þunresdæg Day of Thor).
Fear of thunder is known as
ceraunophobia.
Calculating distance
A flash of lightning, followed after some seconds by a rumble of thunder is, for many people, the first illustration of the fact that
sound travels more slowly than
light. Using this difference, one can estimate how far away the bolt of lightning is by timing the interval between seeing the flash and hearing thunder. The
speed of sound in dry air is approximately 343 m/s or 1,127 feet per second or at 68°F (20 °C).
[4]
The
speed of light is high enough that it can be taken as
infinite in this calculation. Therefore, the lightning is approximately one kilometer distant for every 2.9 seconds (or one mile for every 4.6 seconds). In the same five seconds the light could have travelled the same distance as circling the globe 37 times. Thunder is seldom heard at distances over 24 kilometers (15 miles). A flash of lightning and a simultaneous sharp "clap!" of thunder, a
thunderclap
, therefore indicates that the lightning strike was very near.
See also
- Thunderstorm
- Thunderbolt
- Lightning
- The Castle Thunder sound effect
- List of thunder gods
- Thunder gods category
References
- Lightning?
- Thunder
- P Graneau, The cause of thunder, 1989 J. Phys. D: Appl. Phys. 22 1083-1094 doi:10.1088/0022-3727/22/8/012
- Handbook of Chemistry and Physics, 72nd edition, special student edition