Thunder
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2008-07-14T18:42:14Z
VolkovBot
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robot Adding: [[uk:Грім]]
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<!-- Unsourced image removed: [[Image:Milad_Tower_IRestorer.jpg|right||thumb|350px|A thunderstorm over the Milad Tower in Tehran/[[Iran]].]] -->
'''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. 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.
{| class="infobox"
|{{Listen|filename=Thunder.ogg|title=Thunder|description=A short sample of a ''clap of thunder''|format=[[Ogg]]}}
|}
==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, 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 (physics)|plasma]] in the lightning channel. In a fraction of a second the air is heated to a temperature approaching 28,000 [[Celsius|°C]] (50,000 [[Fahrenheit|°F]])<ref>[http://weathersavvy.com/Q-lightning1.html Lightning?<!-- Bot generated title -->]</ref>. 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, 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 [[overpressure]]s 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.
<ref>P Graneau, The cause of thunder, 1989 J. Phys. D: Appl. Phys. 22 1083-1094 doi:10.1088/0022-3727/22/8/012</ref>
==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 language|Old Norse]] word for thunder.
The shared [[Proto-Indo-European language|Proto-Indo-European]] [[Proto-Indo-European root|root]] is [[wiktionary:Appendix:List_of_Proto-Indo-European_roots#t|*''tón-r̥'']].
See also:
*Thursday (German: ''Donnerstag'': "[[Thor|Thunder]]s Day")
*[[Donner]] und [[Blitz]] (German for "''Thunder and Lightning''")
*[[Tornado]]
==Calculating distance==<!-- This section is linked from [[Five-second rule]] -->
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 1127 feet per second or 768 MPH at 20 °C.
<ref> See, for example, page 14-36 of {{cite book
| title = Handbook of Chemistry and Physics, 72nd edition, special student edition
| publisher = The Chemical Rubber Co. | date = 1991
| location = Boca Raton | pages = | isbn = 0-8493-05625-9}} </ref>
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 circled 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.
==Fear of thunder==
Fear of thunder is known as [[astraphobia]].
==See also==
*[[Thunderstorm]]
*[[Thunderbolt]]
*[[Lightning]]
*[[Castle thunder (sound effect)|The Castle Thunder sound effect]]
*[[List of thunder gods]]
*[[:Category:Thunder gods|Thunder gods category]]
==References==
{{reflist}}
==External links==
* [http://www.lightningsafety.com/nlsi_info/thunder2.html The science of thunder]
[[Category:Atmospheric electricity]]
[[Category:Noise]]
[[Category:Weather]]
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