I’ve always been fascinated by thunderstorms. Can someone explain why we see lightning before we hear thunder, and what exactly causes both of these phenomena?
In: Physics
When you rub your feet on a carpet you build up static electricity. When you get close enough to metal, you get the spark and the sound of a little pop.
Your body is the storm and the metal is the Earth, the spark is lightning and thunder is the pop of the spark.
The storm builds static electricity on a massive scale then releases it on something that’s close enough, whether it’s other parts of the cloud, it the Earth.
Inside the clouds of a thunderstorm, the force of atoms hitting each other at the speeds they do is able to knock electrons out of their orbit. These electrons then become unstable and seek their way towards the closest body (when we mention lightning it’s usually the ground). After so much buildup, large amounts of electrons will make way for that body through the path of least resistance, and at such massive numbers, result in the destructive phenomenon of lightning.
As the lightning traves through the air, the electric charge brings with it immense levels of heat, which cause the air around the strike it to rapidly expand before the temperature rapidly neutralizes and contracts back to its normal state. This expansion and contraction creates a massive soundwave that we then hear as thunder.
Light travels at around 300 000 000 m/s and sound at around 340m/s.
340m/s is close to 3 seconds per kilometer so the sound from lightning 2km away takes close to 6 seconds to reach you.
The time it takes light to travel the same distance is extremely low, we talk about 1/100 of a millionth of a second so we can call it zero.
So you see lightning before you hear thunder because light travels a lot faster than sound.
Thunder is the result of the lightning heating up the air it travels to. If you heat air its pressure increases and it will expand and create a pressure wave that travels outward, sound is a pressure wave. It is fundamentally the same as any explosion, they create high-pressure gases too that expand and create the sound.
Lightning is static electricity between the ground and clouds. It is just like if you rub against something and then get a small static electrical discharge, the voltage and amount of energy is just a lot higher
FYI (til) it takes the sound about 5 seconds to travel one mile (1km in about 3 seconds.)
Flash… boom is dang close.
I haven’t seen the actual lightning flash addressed – the electrical discharge ionizes the molecules in and around the arc path from the cloud to the ground. So you have a bunch of positively and negatively charged atoms that want to go back to neutral. The notice each other and snap back – switching electrons. This snapping creates the flash you see by vibrating in the visible light spectrum.
Interestingly enough, it is the SAME thing that happens with a meteor trail, except the air molecules are energized by frictional heat heat of the meteor passing through the atmosphere. The light of the trail is these ionized molecules snapping back to neutral. The meteor trail lasts longer and is less bright however, because it is happing in the upper atmosphere where everything is less dense, so it takes longer for the ions to find each other – they are fewer and farther apart. So the light isn’t as blinding as lightning and doesn’t happen as quickly.
the eli5 answer is that because of physics sometimes during storms clouds get electrically charged one way or the other. things don’t like to be electrically charged and so when they get too far from neutral they’ll release (or discharge) that electricity. that’s lightning, sometimes it’s to other clouds if for instance one has a strong negative charge and one has a strong positive charge but if it can’t discharge to another cloud it’ll discharge to the ground to go neutral, that’s when lightning strikes the ground (and actually it doesn’t just go one way, it forms a loop)
so that’s the lightning. now one of the things about lightning is it’s VERY hot. in fact because it’s so hot it makes the air it go through expand a lot. when it’s done the air now has a big gap in it from when all of the super hot air expanded and so new air rushes in to fill that gap. that process creates the very loud bang sound that we know as thunder
now the reason you see the lightning before you hear the thunder is actually really simple. light travels at 186282 miles per SECOND. sound travels at 767 miles per HOUR. so for every 5 miles you are away from the lightning strike there will be a second of time gap because the sound needs to catch up to the light. you can’t see it in the US but if you ever see a plane go faster than 800 miles per hour it’s really weird because you’ll see the plane fly overhead completely silently and then just a little bit later you’ll hear a crack and a loud roaring sound and actually feel a breeze from the plane going by and that’s because it’s going faster than the sound it makes (which is bonkersville)
Lightning is an electrical current. The turbulent atmosphere creates areas of opposite charge. Eventually, these charges become so large that they overcome the resistance between them and equalize by conducting a current. This is lightning. We’re talking something like several billion volts (your wall outlet is 120 or 240 volts) and millions of amps (your wall outlet is maybe 15-30 amps). It’s a vast amount of energy, and lightning is exceptionally hot. Perhaps ten times hotter than the photosphere of the Sun.
Thunder is what happens when the lightning superheats the air it’s passing through, creating a shockwave that manifests as sound. It’s so hot that the air expands extremely rapidly. You hear thunder after seeing lightning because light travels at the speed of light, sound travels at the speed of sound, which is much slower. They happen at the same time, but take different amounts of time to reach you.
Even though many seem to believe that it’s some kind of internal rubbing in the clouds, I don’t think it has ever been shown in any real way, and I think it’s false. It’s the photoelectric effect that charges the top of the coulds and the ground positively, and leaves the bottom of the clouds charged negatively.
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. The sound travels slower than the light so you see the light first. https://youtu.be/NQiqXdEHL_Q
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