Thunder and lightning

There’s a thunderstorm underway! What causes these bright flashes of light and the big booms that follow? To find out, we first need to understand a few things about those tiny building blocks that make up matter — atoms — and their charge. Atoms contain protons, electrons, and neutrons. Protons have a positive charge.

Electrons have a negative charge. And neutrons have no charge. Most of the time, atoms have the same number of protons and electrons, so their charge is neutral. But sometimes, electrons jump from one atom to another. An atom that loses electrons becomes positively charged.

And an atom that gains extra electrons becomes negatively charged. What does this have to do with thunder and lightning? We’re getting there! Let’s take a look at how charged atoms behave... Have you ever walked across a fuzzy carpet, then reached for a doorknob and got a little shock?

This is because you picked up a negative charge from the carpet. Negative charges repel other negative charges, and attract opposite, positive, charges. Opposite charges attract; same charges repel. So when you touched the doorknob, your body’s negative charge was attracted to the positive charge in the metal. The shock you felt was electrons flowing super fast from you to the doorknob.

You might say the electrons flowed at lightning speed! That’s right, lightning is just like an electric shock, but on a much bigger scale. The clouds we see during a thunderstorm contain water droplets, ice crystals and hail. As these particles move around in the thundercloud, electrons jump between them. Many of the ice crystals become positively charged, and much of the hail becomes negatively charged.

The ice crystals are light, and are carried upward by rising air, while the hail is heavier, and falls downward to the lower part of the cloud. So the upper part of the cloud becomes positively charged and the lower part becomes negatively charged. The negatively charged particles in the cloud repel negatively charged particles in the ground beneath. This causes the negatively charged particles in the ground to be pushed deeper into the earth. The ground on the surface becomes positively charged.

Now, the negatively charged particles in the cloud are attracted to the positively charged ground. Electrons from the cloud rush to the ground… as a bolt of lightning! What about the thunder that follows — where does that sound come from? As the lightning bolt shoots from the sky to the ground it heats the air it travels through. This sudden rise in temperature makes the air expand, rapidly.

Our ears hear this shockwave as a loud bang or crackle — thunder! Light travels through air much faster than sound. That’s why you often see a flash of lightning first, and then hear the thunder a few seconds later. So now you know: lightning happens when an electrical charge builds up inside a cloud and shoots to an opposite charge on the ground. And thunder happens when the heat from lightning causes the air around it to expand suddenly.

If you see lightning, and hear thunder almost immediately, you know the lightning is very close. It’s time to take shelter!