Why does the wind make giant waves out at sea but not in a pond?
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After you watchWhy does the wind make giant waves out at sea but not in a pond?
The short answer
Wind speed, duration and fetch—the distance over open water—all affect wave growth. A long fetch does not guarantee larger waves if the wind blows only briefly.
Try this next
- What can you compare on replay? At each still, compare both clocks and wave heights. Explain why the longer stretch has not reached its potential by its earlier stopping time.
Now you — bend it
- What if What would change with more time?Sketch a new prediction from the ingredients; the on-screen test keeps its starting values fixed.
Can you prove it?The result depends on the specified starting conditions. — At each still, compare both clocks and wave heights. Explain why the longer stretch has not reached its potential by its earlier stopping time.
Design your own test:Choose a new time and predict before calculating; distinguish the paper extension from the fixed on-screen test.
Explain it to a 6-year-old: Wind speed, duration and fetch—the distance over open water—all affect wave growth. A long fetch does not guarantee larger waves if the wind blows only briefly.
The whole story
How it works
The illustrative model adds energy at rate 1 minus energy divided by fetch. Its finite-time energy is F × (1 − exp(−t/F)), with height proportional to the square root of energy. A uses fetch 2 and duration 8; B uses fetch 8 and duration 1. Their final relative heights are about 1.40 and 0.97.
What people get wrong
These are dimensionless teaching units, not a calibrated marine forecast. Real wave growth also involves wind changes, depth, breaking, currents and swell from elsewhere. The drawing is not a safety guide.
The catch
These are dimensionless teaching units, not a calibrated marine forecast. Real wave growth also involves wind changes, depth, breaking, currents and swell from elsewhere. The drawing is not a safety guide.
Questions kids ask
Why does the wind make giant waves out at sea but not in a pond?
Wind speed, duration and fetch—the distance over open water—all affect wave growth. A long fetch does not guarantee larger waves if the wind blows only briefly.
What does the experiment measure?
The illustrative model adds energy at rate 1 minus energy divided by fetch. Its finite-time energy is F × (1 − exp(−t/F)), with height proportional to the square root of energy. A uses fetch 2 and duration 8; B uses fetch 8 and duration 1. Their final relative heights are about 1.40 and 0.97.
What does the model leave out?
These are dimensionless teaching units, not a calibrated marine forecast. Real wave growth also involves wind changes, depth, breaking, currents and swell from elsewhere. The drawing is not a safety guide.
Talk about it
- Which run ends with taller waves: a short fetch with longer wind, or a long fetch with brief wind?
- What did you count or measure?
- Which parts of the real world does this model leave out?
For grown-ups
The illustrative model adds energy at rate 1 minus energy divided by fetch. Its finite-time energy is F × (1 − exp(−t/F)), with height proportional to the square root of energy. A uses fetch 2 and duration 8; B uses fetch 8 and duration 1. Their final relative heights are about 1.40 and 0.97. These are dimensionless teaching units, not a calibrated marine forecast. Real wave growth also involves wind changes, depth, breaking, currents and swell from elsewhere. The drawing is not a safety guide.
Keep going
What else makes you wonder?
- What would change if you gave both runs more time?
- Which observations would test your new prediction?
