Lightning creates thunder. Lightning is an electrical discharge that heats a channel in the air to a plasma - about 11,000 degrees Celsius. This super heated plasma then explodes outward into the surrounding, normal-temperature air with incredible force, generating a shockwave. This shockwave is the thunderclap.

Because shockwaves tend to blur as they travel great distances, the thunder has generally turned into a low rumbling boom by the time it reaches you and is no longer a shockwave, but it is when the lightning strikes.

Sound also travels at a finite speed, about 1000 feet per second. The flash from the lightning also travels at a finite speed, but it's much faster, about 186,000 *miles* per second. This means that you see the flash before you hear the thunderclap, because the sound waves haven't gotten to you yet when the light has.

Thunder and lightning are the very same event, that is caused by massive and sudden electric charge transfer inside clouds. This event creates both sound and light, but because light travels much much faster than sound, we see light first (which we would call lightning), and hear the sound later (which is called a thunder).

The sound of thunder comes from lightning, and you can’t have one without the other. During a storm, electrical charge builds up in clouds, with an opposite charge building up on the earth below, like a huge battery. When the charge gets high enough, the energy that has been built up is released as a lightning bolt. As this energy is released, the air around the lightning bolt reaches a very high temperature and pressure. The pressurized region travels outward from the lightning bolt as a wave, reaches your ear, and you hear the rumble of thunder.

Thunder is actually the sound that results from lightning, which causes a sudden increase in pressure and temperature in the air surrounding and inside of the lightning bolt. This change in temperature and pressure causes the air to expand very quickly, producing vibrations of the air molecules which are manifested as sound.

Thunder and lightning are both part of the process when there's a huge electric spark in the atmosphere. We see the light right away, because light travels so fast - about 300 million meters every second. Sound travels almost 1000 times slower, so it is slow to reach us.

Do you know that you can tell how far away the lightning was by how long it takes to hear the thunder? It takes the thunder 5 seconds to go 1 mile, so you can count the seconds and that tells you how many miles away the lightning was.

The huge spark in the atmosphere makes huge amounts of air move, and that makes the thunder sound.

Light is light, and sound is sound, so they're different. Sometimes the same thing can cause both light and sound, like the storms that cause thunder and lightning.