Have you ever been in a thunders storm? Here’s how you can use wave speed to figure out how far away that lightning strike really was.

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When there’s lightning, thunder is not far behind.  Even if you don’t live in a tropical thunderstorm area, you can still simulate this experiment using the variations below and get the most out of the main ideas about sound waves and light waves.

For starters, let’s assume you’re waiting for a good storm. When one’s brewing, grab a timer and a pencil with paper and wait inside the house near a window.

Here’s what you need:

• two hunks of wood or a pair of baseball bats
• a neighborhood block
• a partner

1. Wait until you see a lightning flash (do this indoors please!).

2. Start your timer (or count “one Mississippi, two Mississippi”, etc.)

3. Stop counting when you hear the thunder.

4. Take whatever number you’ve reached and divide it by 5. That number is how many miles the lightning strike is away from you. So if you’ve counted for about 3 seconds the lightning strike is about a half mile away. If you’ve counted for 5 seconds the lightning is 1 mile away. If you’ve counted for 8 seconds the lightning is about 1.5 miles away.

Remember, sound travels at about 1000 ft/sec. A mile is a little over 5000 feet (5280 ft. to be exact). So it takes sound about 5 seconds to go 1 mile!

“Advanced students: Download your Thunder and Lightning”

Want to do this experiment without a storm?

You’ll need two hunks of wood or a pair of baseball bats, a neighborhood block, and a partner.

1. Give your partner the two bats or hunks of wood.

2. Have them walk a half a block away or at least 250 feet.

3. When they get there have them clack together the two pieces of wood (be careful not to smash fingers, you want to hear the wood, not the scream of you friend!).

4. Have them do it several times. Try to notice a difference between when you see the wood crashing together and when you hear it. If you don’t hear a difference, get farther apart from one another.

5. Trade places so that your partner can see the delay of sound (just like on one of those old Japanese movies).

Sound travels at about 760 mph. That’s the same as about 1000 ft/sec. If your friend was standing about 250 feet away from you, it took a quarter of a second for the sound to get from your partner to you.

The next time you’re at a baseball game or a fireworks display try to time the difference between the time you see something and the time you hear something. Remember that sound travels 1000 ft/sec. If the distance is great enough you may be able to figure out how far away it is and amaze your friends!

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