Why Lightning, Then Thunder?
Learners can explain why lightning is seen before thunder is heard, estimate the distance to a storm from the time gap between flash and rumble, and recognize the limits of that estimate.
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Why do we see a flash of lightning before we hear the thunder that follows it, and can the delay tell us how far away a storm is?
- same-event-different-signals
- Lightning and thunder are two different signals — light and sound — produced by the same event at the same place and time.
- speed-gap
- Light travels through air almost instantly at everyday distances, while sound crawls along at roughly 340 m/s — a huge gap in speed.
- count-seconds-distance
- Counting seconds between flash and rumble and multiplying by ~340 m/s gives the distance to the strike.
- rill-quote-rule
- Every rough rule of thumb ('5 seconds per mile', '3 seconds per kilometer') is an analogy — useful as a memory aid, not a literal mechanism.
- uncertainty-of-estimate
- The estimate is uncertain: sound speed varies with temperature and wind, thunder is drawn out by echoes from clouds and terrain, and human reaction time is not zero.
Thunder is made after the lightning, in a different place, by the cloud.
Show that thunder and lightning are produced at the same place and time; the gap we hear is just sound arriving late.
If I count to three the storm is about three kilometers away — that's a precise distance.
Demonstrate the uncertainty: temperature, wind, echoes, and reaction time mean the count gives an estimate with a real error margin, not a precise number.
- How a thunderstorm forms
- Charge separation and stepped leaders
- Light/sound speed in other media
- Doppler effects of storms
- Safety advice beyond one line (this is a thinking course, not a safety briefing)
- Learner explains in their own words why lightning is seen before thunder is heard.
- Learner applies the count-seconds-and-multiply rule to estimate a storm's distance from a given gap.
- Learner names at least one source of uncertainty in the estimate.
- Given a real observation (a later thunderstorm, or a video of one with a time stamp), the learner can carry out the count-and-multiply method and report a distance with a stated uncertainty.
Curious general learners aged 13 and up with no prior physics background. They can do basic multiplication and division with whole numbers, but no formulas are required.
- 01A Familiar Surpriseslide
- 02Your First Guessinteractive
- 03Same Place, Same Momentslide
- 04Speed Raceinteractive
- 05From Delay to Distanceslide
- 06Try the Methodinteractive
- 07Why the Rumble Drags Onslide
- 08How Precise Is Your Count?interactive
- 09Estimate a Real Storminteractive
- 10What We Have, What We Don'tslide
- 11A New Questionslide
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