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'Thunder' is the sound made by lightning. Depending on the nature of the lightning and distance of the hearer, it can range from a sharp, loud crack to a long, low rumble. It is produced by a sonic shock wave caused by the rapid expansion of the air surrounding and within a bolt of lightning.

Contents

The cause of thunder

Etymology

Calculating distance

Fear of thunder

See also

References

External links

The cause of thunder

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 along its path, and that thunder was caused by the subsequent motion of air rushing to fill the vacuum. Later in the 19th century it was believed that thunder was caused by an explosion of steam when water along the lightning channel was heated. Another theory was that gaseous materials were created by lightning and then exploded. 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, 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 bolt of lightning.
^[2]

Etymology

The ''d'' in ''thunder'' is epenthetic, and is now found in Modern Dutch ''donder'', from earlier Old English ''þunor'', Middle Dutch ''donre'', together with Old Norse ''þorr'', Old Frisian ''þuner'', Old High German ''donar'' descended from Proto-Germanic
★ ''þunraz''. In Latin it's ''tonare'' "to thunder" (see also tornado). The name of the Germanic god Thor comes from the Old Norse word for thunder.
See also:

★ Thursday (German: ''Donnerstag'': "Thunders Day")

★ Donner und Blitz (German for "''Thunder and Lightning''")

★ tornado

Calculating distance

A flash of lightning, followed after some seconds by a rumble of thunder, is for many people the first illustration of the the fact that sound (like light) does not travel instantaneously, and that sound is by far the slower. 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 air is approximately 344 m/s or 769 mph. The speed of light can be assumed to be infinite in this calculation because one must know that there has been a lightning strike before starting counting. Therefore, the lightning is approximately one kilometer distant for every three seconds (or one mile for every five seconds). Thunder is seldom heard at distances over 15 miles.

Fear of thunder

Fear of thunder is known as astraphobia.

See also

★ Thunderstorm

★ Thunderbolt

★ Lightning

★ The Castle Thunder sound effect

★ List of thunder gods

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References

1. http://weathersavvy.com/Q-lightning1.html
2. P Graneau, The cause of thunder, 1989 J. Phys. D: Appl. Phys. 22 1083-1094 doi:10.1088/0022-3727/22/8/012

External links

★ The science of thunder