How Thunder Is Made — Simple Step-by-Step Explanation for a 9-year-old

What makes thunder?

Thunder is the loud sound you hear during a storm, and it happens because lightning heats the air very quickly. Here is how that works step by step:

1. Charges separate in the cloud. Inside a storm cloud, little ice and water pieces bump into each other. This makes parts of the cloud get a positive electric charge and other parts get a negative charge.
2. Electricity finds a path. When the difference in charge gets big enough, electricity jumps through the air to connect the charges. That jump is lightning.
3. Lightning heats the air. The lightning bolt heats the air next to it to a very high temperature (much hotter than the surface of the sun) in a tiny fraction of a second.
4. The air expands suddenly. The super-fast heating makes the air expand almost like a small explosion. That fast expansion pushes on the air and creates a shock wave — a sudden change in air pressure.
5. The shock wave becomes sound. The shock wave moves away from the lightning and we hear it as thunder.

Quick idea: Lightning makes the air explode, and the explosion makes the sound we call thunder.

Why does thunder sound different sometimes?

• If lightning is close, thunder can sound like a sharp crack or a loud crack like a whip.
• If lightning is far away, the sound stretches out into a rumble because the sound bounces around clouds, hills, and buildings before it reaches you.
• The shape of the lightning bolt (straight or jagged) and how the air is layered also change the sound.

Why you see lightning before you hear thunder

Light travels almost instantly to your eyes, but sound travels much slower. So you see the flash first, and then, a little later, you hear the thunder. You can use the delay to guess how far away the storm is:

• Count the seconds between the flash and the thunder. Divide by about 3 to get the distance in kilometers, or divide by about 5 to get miles. (Example: 9 seconds ÷ 3 = 3 km away.)

Safety tip

Thunder means lightning is nearby. If you hear thunder, go indoors and stay away from tall objects and open water until the storm has passed.

Short recap: Lightning quickly heats the air, the heated air expands and makes a shock wave, and that shock wave is the thunder you hear.