The Sound of Thunder> Sound never sits still. If there’s sound in the air, it’s moving, spreading out in all directions. That’s because sound is a special kind of traveling vibration called a <#5677,6><!wave>. Once you make a wave, it always moves out away from where you made it. When lightning strikes, it makes a loud sound (thunder) that travels sometimes many miles to where you hear it.
But have you ever wondered why you hear the thunder only after you see the flash of lightning? Because it takes the sound a lot longer to reach you than it does the light. Both light and sound are made in the same instant that the lightning strikes. The light zips to your eye at a speed of 186,282 miles per second (299,784 kilometers/second). You see the flash in less than the blink of an eye! But the sound just moseys along at a jet-speed of 750 miles per hour (1200 kilometers per hour). At that <#5678,4><!speed>, it takes about 5 seconds for sound to go a mile.
Try this experiment during the next big storm: right after you see a flash of lightning, begin to count out loud (“one thousand one, one thousand two. . .”). Stop when you hear the thunder. How far did you get? If you counted to ten, it took you ten seconds. At five seconds a mile, that means the sound traveled about two miles to reach your ears.
If you keep track of the flashes and thunders, and write down the times and distances, you can use the sound of thunder to tell if the lightning is getting closer or farther away!
