Why is lightning so loud?
In: 31
Lightning superheats the air around its entire length. This sudden, extreme increase in temperature causes it to expand rapidly, just like when explosives are detonated. That rapid expansion creates a pressure wave that our ears interpret as sound.
Because it’s really hot, and it makes the air incredibly hot in a very short amount of time.
Sound is a moving pressure wave. When a lightning strike occurs, it heats the air it’s passing through to tens of thousands of degrees in an instant. ~~Pressure is equal to volume times temperature~~ Pressure is equal to force divided by area (corrected per /u/Astronautmatt below); Force is mass (of the displaced air) times acceleration. Lightning doesn’t displace a whole lot of air, but the rapid heating of the air does result in a very high acceleration, so the lightning has a lot of force. This forces the air molecules around the lightning strike to travel away from the strike location, propagating the sound wave away from the strike. The area bounding the lightning strike is decently large, but the acceleration component of the force is so huge that it overwhelms the rest of the equation, resulting in a large pressure spike. Because of the spike in pressure, the sound waves have a large amplitude, which our brains interpret as a large volume.
To add to the other answers, what you get at the location of the lightning strike is an actual shockwave. A shockwave is a bit different from just a pressure wave in that it moves above the speed of sound. It loses energy rapidly and will eventually become a pressure wave, but it starts basically like a shockwave an explosive would set off.
It’s also why a plane flying at supersonic speeds is so loud, going faster than the speed of sound creates a shockwave as well.
If you’ve used or use firearms, you might know the difference in noise between rounds that are subsonic and supersonic.
If you’re ever near a lightning strike, you can actually feel the vibration from the resulting shockwave. I’ve had it strike near enough to shake the entire house before. Since light travel faster, you can sometimes tell by the flash that you’ll feel the vibrations soon.
Lightning is created by a build up of static electricity at the base of a cloud, when this charge is released it transforms the air into superheated plasma which glows brilliantly. The heat created in the lightning causes the air to expand creating a shockwave which we hear and feel as thunder. https://youtu.be/NQiqXdEHL_Q
Latest Answers