Thunder

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Thunderbirds :: Thunderpants :: Thunder_Road :: Thunderbugs :: Thundercats :: Thunders,_Johnny :: Thunderball :: Thunderbird :: Thundersley :: Thunderstrike_-_Operation_Phoenix

For other uses, see (disambiguation).

Thunder is the sound of the shockwave caused during a thunderstorm when lightning rapidly heats and expands the air in and directly around the lightning channel (bolt) into plasma, producing acoustic shock waves in the atmosphere indentified as thunder. It is said that the air is heated up to 30 000 °C (54 000 °F). This phenomenon happens at the same time (lightning strike/air expansion thunderclap), but we hear thunder after we see lightning due to the simple fact that light travels at a faster speed than sound. However, at a close enough distance to the actual lighting strike point, both sound and light can be heard/seen simultaneously. The exact mechanism is poorly understood.

Theories of the cause of thunder

The cause of thunder has been the subject of centuries of speculation and scientific enquiry. The first recorded theory is attributed to 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 shockwave in the air due to the sudden thermal expansion of the plasma in the lightning channel.

Experimental support for this theory came from spectroscopic temperature measuring up to 36000 Kelvin. Arc photography then proved that the plasma did not expand thermally in all directions, but preferentially at right angles to the electric current. According to Graneau, the mechanism for this is not yet completely understood in terms of magnetohydrodynamics.

Etymology

The d in thunder is epenthetic, and is not found in Modern Dutch donder, from earlier d-less Old English þunor, Middle Dutch donre, together with Old Norse þorr, Old Frisian þuner, Old High German donar descended from Proto-Germanic *þunraz, built on a PIE stem *' also found in Sanskrit ' "thundering", Latin tonare "to thunder" (see also tornado).

Calculating distance

Since sound and light travel at different speeds through the atmosphere, one can estimate how far away the bolt of lightning is by timing the interval between seeing the flash and hearing the thunder. The speed of sound in air is approximately 332 m/s (742.6 mph). The speed of light is so fast that it can be ignored in this calculation. Therefore, the lightning is approximately one kilometer distant for every 3 seconds (or one mile for every 5 seconds).