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When there's a thunderstorm, the same thing always happens: first you see the lightning, then after a few seconds the thunder arrives. That delay is no mystery: it's a consequence of the fact that light and sound travel at very different speeds. And it's precisely this difference that allows us to estimate how far away the thunderstorm is.
Let's see how it works, with a simple but precise approach.
🌩️ Light: extremely fast
Lightning travels at about 300,000 km per second. It's so fast that, even if the storm is tens of kilometers away, the light reaches us practically instantly.
This is why, when we see lightning, we can consider the arrival time of the light to be practically zero.
🔊 Sound: much slower
Thunder, on the other hand, is a sound wave that travels through the air at about 343 meters per second (at room temperature). This means it takes:
- about 3 seconds to travel 1 km,
- 1 second every 343 meters.
That's why we feel it delayed.
⏱️ The trick to calculating distance
When you see the lightning, simply start counting the seconds until you hear the thunder.
Then you can estimate the distance in two ways:
1. With the simple (and widely used) rule:
👉 Every 3 seconds ≈ 1 km
It's an approximation, but it works well in real life.
2. With a simple (but stress-free) formula:
If you want to be a little more precise:
Distance ≈ seconds × 343mFor example, if 5 seconds pass:
5 × 343 ≈ 1,700 meters, so approximately 1.7 km.
🧠 Why does this work?
Because in our calculation, light arrives immediately, while sound arrives later: the delay is directly proportional to the distance of the lightning.
It's a small example of physics accessible to everyone: no special tools, just our senses and the fact that the world moves at different speeds.
🌧️ Next time... try it!
Next time the storm hits, do a simple experiment:
- Watch the lightning
- Count calmly
- Listen to the thunder
- Guess the distance
It's a fun way to approach science without complicated formulas, but with the right amount of precision.
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