S3.9.7 For the adult
The speed of sound
Why do I see lightning first and hear the thunder later?
What this chapter teaches
Sound goes about 340 metres each second in air, faster in water and faster still in solids. Light is far faster, so the flash arrives almost at once. Counting seconds from flash to thunder and dividing by 3 gives the storm distance in kilometres.
Three questions to ask
There is no one right wording. Listen for the idea.
- Why do we see lightning before we hear thunder?
- You count 12 seconds from flash to thunder. About how far away is the storm?
- Where should you be when you count, and why?
After the chapter, the learner can
- Explain why we see lightning before we hear thunder
- Estimate a storm's distance by counting from flash to thunder
What they copy into their notebook
Light is far faster than sound, so we see lightning first. Sound goes about 340 m/s. Divide the seconds from flash to thunder by 3 to find the kilometres.