Science Bell Ringer for Grades 6–8: Timing thunder to find a storm’s distance
A free science bell ringer for grades 6–8. Put the prompt on the board as students walk in, give them three to five minutes, then go over it together. The answer and teacher notes are in the box below the prompt.
The prompt
You see a flash of lightning and count 10 seconds before you hear the thunder. About how many miles away was the lightning? Explain why you see the flash before you hear the sound, even though both happen at the same moment.
Answer and teacher notes
The National Weather Service rule: count the seconds and divide by 5. 10 ÷ 5 = about 2 miles. Check another way: sound travels about 1,100 feet per second near sea level, so 10 × 1,100 = 11,000 feet, and 11,000 ÷ 5,280 ≈ 2.1 miles.
Light travels almost a million times faster than sound, so the flash reaches you nearly instantly while the sound takes several seconds. Safety note worth sharing: thunder can only be heard about 10 miles away, so if you can hear it, you are close enough to be struck. Count from indoors.
Sources: National Weather Service: Understanding Lightning: Thunder; NASA Glenn Research Center: Speed of Sound
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