Thunder: Wikis

  
  

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Thunder is the sound made by lightning. Depending on the nature of the lightning and distance of the listener, thunder 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, often referred to as a clap, crack, or peal of thunder.

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Contents

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. The temperature inside the lightning channel, measured by spectral analysis, varies during its 50 μs existence, rising sharply from an initial temperature of about 20,000 K to about 30,000 K, then dropping away gradually to about 10,000 K. The average is about 20,400 K (20,100 °C; 36,300 °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, the consensus around the cause of the shock wave 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-r̥ 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 768 mph (1,236 km/h) at 20°C (68 °F). [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 that elapse between the visible flash and the first sound of thunder (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 20 kilometers (12 miles)[5]. A flash of lightning and a simultaneous sharp "crack!" of thunder, a thundercrack, therefore indicates that the lightning strike was very near.

See also

References

  1. ^ Cooray, Vernon (2003). The lightning flash. London: Institution of Electrical Engineers. pp. 163–164. ISBN 0852967802. 
  2. ^ "Thunder". Encyclopædia Britannica. http://www.britannica.com/EBchecked/topic/594339/thunder. Retrieved 2008-09-12. 
  3. ^ P Graneau, The cause of thunder, 1989 J. Phys. D: Appl. Phys. 22 1083-1094 doi:10.1088/0022-3727/22/8/012
  4. ^ See, for example, page 14-36 of Handbook of Chemistry and Physics, 72nd edition, special student edition. Boca Raton: The Chemical Rubber Co.. 1991. ISBN 0-8493-05625-9. 
  5. ^ "Thunder". Encyclopædia Britannica. http://www.britannica.com/EBchecked/topic/594339/thunder. Retrieved 2008-09-12. 

External links


1911 encyclopedia

Up to date as of January 14, 2010

From LoveToKnow 1911

THUNDER, the noise which accompanies or follows a flash of lightning, due to the disturbance of air by a discharge of electricity (see LIGHTNING; ATMOSPHERIC ELECTRICITY and METEOROLOGY). The Old English word is bunor, also the name of the Scandinavian god Thor, which is cognate with Dutch donder, German Donner. The root is than,- Indo-European tan-, cf. Latin tonare, tonitru. This root is apparently another form of stan-, as in Skr. .stare, to sound, thunder, Gr. to groan, Eng. "stun."


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Bible wiki

Up to date as of January 23, 2010

From BibleWiki


often referred to in Scripture (Job 40:9; Ps 7718; 104:7). James and John were called by our Lord "sons of thunder" (Mk 3:17). In Job 39:19, instead of "thunder," as in the Authorized Version, the Revised Version translates (ra'amah) by "quivering main" (marg., "shaking"). Thunder accompanied the giving of the law at Sinai (Ex 19:16). It was regarded as the voice of God (Job 37:2; Ps 1813; 81:7; comp. Jn 12:29). In answer to Samuel's prayer (1Sam 12:17, 18), God sent thunder, and "all the people greatly feared," for at such a season (the wheat-harvest) thunder and rain were almost unknown in Palestine.

This entry includes text from Easton's Bible Dictionary, 1897.

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This article needs to be merged with THUNDER (Jewish Encyclopedia).

Simple English

For the aircraft, see P-47 Thunderbolt and A-10 Thunderbolt II.

Thunder is a very loud sound that is made sometimes during a very big rain storm. Thunder is so loud, it can be heard from a very far distance. It can sound like a boom, a crash, or a rumble.

Thunder is made when lightning strikes. The energy from the lightning heats up the air so much that it makes a kind of explosion.

When lightning is very near, thunder will be heard soon after the lightning flash, and the sound will be very loud. If the lightning is farther away, the thunder will be a few seconds or many seconds after the lightning. People can guess how far away the lightning is by counting the number of seconds between the time they see the lightning and hear the thunder.








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