Bending by Depth (Refraction)
Waves travel slower in shallow water. Imagine a wave approaching a coastline at an angle. One end of the wave hits shallow water first and slows down. The other end is still in deep water and stays fast.
The wave pivots. It bends toward the shallow water. This is why waves always seem to face the beach when they break, even if the wind is sideways.
Bending by Obstacle (Diffraction)
This happens when a wave hits a solid object like a harbor wall or a small island. The wave is sliced in half.
As the wave passes the wall, energy "leaks" sideways into the calm water behind the wall. The wave wraps around the corner in a semi-circle. This reduces the wave height significantly but spreads it out.
Comparison
Refraction
Bends due to depth
Wave pivots toward shallow water
Effect: Focuses energy (bigger waves)
Diffraction
Bends around obstacles
Wave wraps in semi-circles
Effect: Spreads energy (smaller waves)
Practical Application
Refraction focuses energy (makes waves bigger). Diffraction spreads energy (makes waves smaller but cleaner).
Look for spots protected by breakwaters or islands if you want smaller, cleaner waves. Avoid headlands if you want to avoid focused, larger waves.
Combined Effects
In reality, both effects happen together. A wave approaching a headland will refract due to the shallow water and diffract around the point. Understanding both helps you predict wave behavior at complex coastlines.
Summary
Refraction focuses energy (makes waves bigger). Diffraction spreads energy (makes waves smaller but cleaner).
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