Dear Zbigniew Motyka

May i know its nature whether it is of longitudinal or transverse?

with regrds

vasanth

There is no difference between lightning and a lightning bolt. They are two phrases that mean the same.

Distant lightning has its thunder travel farther. Because the higher frequencies travel faster than the lower frequencies, when the thunder sound reaches us, it sounds like furniture falling down stairs, and not like a sudden bang.

Ian, I’m not so sure the velocity of propagation of sound in air varies (particularly) with frequency. Certainly the attenuation of sound in air varies, considerably, higher freqs attenuated more than low freqs. This accounts for the low pitch rumbling of distant thunder...

Dear Ian kennedy sir

May I know how a single shock wave created during lightning produces many sounds likewise you said furniture falling down the stairs.Does it hits something on its path of propagation?

regards

vasanth

The sound of the single, quick "BOOM!" of the exploding air travels through the intervening air and is subject to effects such those produced by its multi-path transmission through layers (channels) of air at different densities and humidities, and reflections off any nearby solid objects like the ground, buildings and mountains. This causes distortions of every type in its propagation. The sound is subject to frequency-dependent retardation, phase changes, and frequency-dependent amplitude attenuation. In general, high frequency sound travels faster (and is attenuated the least). The components of the original quick "BOOM" sound reach the distant listener at different times (and/or amplitudes) because of the differing propagation times (and/or attenuation) with frequency. So as it reaches the distant listener, it arrives as a long, spread out (tailing off) "BEM Bim Bom bum". "I have fallen downstairs!"

The original sound can be regarded as a Dirac Delta Function, and the actual intervening air path can be regarded as revealing its overall characteristics directly in the nature of the output, as the distortions are only caused by the intervening medium. (Clap your hands to test the acoustics of your lecture hall.)

Ian, can you provide literature citations to support your assertions that the velocity of sound in air varies with frequency and that the attenuation of high frequency sounds in air is less than for low frequency sounds please? Regards Jonathan

@ Jonathan David Binnington -- The Wikipedia page states " In dry air, the speed of sound increases by about 0.1 m/s as the frequency rises from 10 Hz to 100 Hz. " It is the bass notes which are mainly affected. https://en.wikipedia.org/wiki/Speed_of_sound#Practical_application_to_air

@ Jonathan David Binnington -- Thanks! I have edited last night's late post. The literature shows at 1 kHz that higher frequencies are attenuated more.

"The attenuation of sound in air due to viscous, thermal and rotational loss mechanisms is simply proportional to f2."

http://www.kayelaby.npl.co.uk/general_physics/2_4/2_4_1.html

This explains why very, very distant thunder is mainly bass.

So,

• if you hear thunder as a single sharp event, then run inside immediately. WoW! That was close! (The next flash, you may not be so lucky.)
• If you hear thunder as a multiple event, spread over seconds, walk purposefully inside.
• If you hear thunder as a low continuous, dull sound, you are safe for now. Bring the washing in.