Thunder is the sound caused by lightning. Depending on the distance from and nature of the lightning, 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 within and surrounding the path of a lightning strike. In turn, this expansion of air creates a sonic shock wave referred to as a "thunderclap" or "peal of thunder"; the d in Modern English thunder is epenthetic, is now found as well in Modern Dutch donder. In Latin the term was tonare "to thunder"; the name of the Nordic god Thor comes from the Old Norse word for thunder. The shared Proto-Indo-European root is *tón-r̥ or *tar- found Gaulish Taranis and Hittite Tarhunt; the cause of thunder has been the subject of centuries of speculation and scientific inquiry. Early thinking was that it was made by deities but the ancient Greek philosophers attributed it to natural causes, such as wind striking clouds and movement of air within clouds.

The Roman philosopher, Lucretius held. By the mid-19th century, the accepted theory was. 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 from an initial temperature of about 20,000 K to about 30,000 K dropping away to about 10,000 K. The average is about 20,400 K; this heating causes a rapid outward expansion, impacting the surrounding cooler air at a speed faster than sound would otherwise travel. The resultant outward-moving pulse is a shock wave, similar in principle to the shock wave formed by an explosion, or at the front of a supersonic aircraft. Experimental studies of simulated lightning have produced results consistent with this model, though there is continued debate about the precise physical mechanisms of the process. Other causes have been proposed, relying on electrodynamic effects of the massive current acting on the plasma in the bolt of lightning.

The shock wave in thunder is sufficient to cause property damage and injury, such as internal contusion, to individuals nearby. Thunder can rupture the eardrums of people nearby. If not, it can lead to temporary deafness. Vavrek et al. reported that the sounds of thunder fall into categories based on loudness and pitch. Claps are loud sounds containing higher pitches. Peals are sounds changing in loudness and pitch. Rolls are irregular mixtures of pitches. Rumbles are less loud, last for longer, of low pitch. Inversion thunder results when lightning strikes between cloud and ground occur during a temperature inversion. In an inversion, the air near the ground is cooler than the higher air. Within a temperature inversion, the sound energy is prevented from dispersing vertically as it would in a non-inversion and is thus concentrated in the near-ground layer. Cloud-ground lightning consist of two or more return strokes, from ground to cloud. Return strokes have greater acoustic energy than the first.

The most noticeable aspect of lightning and thunder is that the lightning is seen before the thunder is heard. This is a consequence of the much greater speed of light than of speed of sound. Sound in dry air is 343 m/s or 1,127 ft/s or 768 mph at 20 °C; this translates to 3 seconds per kilometre. A bright flash of lightning and an simultaneous sharp "crack" of thunder, a thundercrack, therefore indicates that the lightning strike was near. Close-in lightning has been described first as a clicking or cloth-tearing sound a cannon shot sound or loud crack/snap, followed by continuous rumbling; the early sounds are from the leader parts of lightning the near parts of the return stroke the distant parts of the return stroke. Thunderbolt Thunderstorm Brontophobia Castle Thunder sound effect Lightning List of thunder gods Mistpouffers Media related to Thunder at Wikimedia CommonsThe science of thunder Thunder: A Child of Lightning Wikibooks: Engineering Acoustics/Thunder acoustics

Christian Volckman

Christian Volckman is a French film director and painter. He is a graduate of Ecole Supérieure d'Arts Graphiques in Paris, he is known for his motion capture animation feature film Renaissance, with the English voices of Daniel Craig, Romola Garai, Jonathan Pryce, Ian Holm, which won the Feature Film Award at the Annecy International Animated Film Festival. In 2006 and Best Feature Film at the 5th Festival of European Animated Feature Films and TV Specials in 2007; the film, distributed by Miramax, received mixed reviews. His other film work includes music videos and two shorts, Le cobaye, which received a Prix du Jury at Annecy in 1995, Maaz, shown at nearly 100 festivals and won 30 prizes, including two for sound. Volckman has directed several music videos, including "Miss Chang" and " Once upon a Time" for the group Chinese Man. "Paris sera toujours Paris", "Sous le ciel de Paris" and "Champs Elysées" for the singer ZAZ. "Requiem" is the song for Alma that represents France at the Eurovision 2017.

In 2008, he and visual artist Raphael Thierry started the website ©®, an artistic collaboration developing thematic films and exhibitions named THEFLOW. He is scheduled to direct The Room, with Justin Chatwin, he is developing two other films: Rapaces, produced by Oriflammes Films, The Kid, produced by Bidibul productions and Superprod. Motion capture List of animated feature films WEBSITE THEFLOW ©® Christian Volckman on IMDb Interview with Christian Volckman