Lightning
Properties

Lightning causes thunder, a sound from the shock wave which develops as gases in the vicinity of the discharge heat suddenly to very high temperatures. It is often heard a few seconds after the lightning itself. Thunder is heard as a rolling, gradually dissipating rumble because the sound from different portions of a long stroke arrives at slightly different times.

When the local electric field exceeds the dielectric strength of damp air (about 3 MV/m), electrical discharge results in a strike, often followed by commensurate discharges branching from the same path. Mechanisms that cause the charges to build up to lightning are still a matter of scientific investigation. A 2016 study confirmed dielectric breakdown is involved. Lightning may be caused by the circulation of warm moisture-filled air through electric fields. Ice or water particles then accumulate charge as in a Van de Graaff generator.

Researchers at the University of Florida found that the final one-dimensional speeds of 10 flashes observed were between 1.0 × 10 and 1.4 × 10 m/s, with an average of 4.4 × 10 m/s.
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