The Flow of Wet Water: Feynman's Physics Explained
Real fluids have viscosity — internal friction — which makes things much harder and far more interesting, and is the source of drag on a moving object. The character of the flow is set by a single number, the Reynolds number, comparing inertia to viscosity. At low Reynolds number flow is smooth and orderly; at high Reynolds number it breaks into chaotic turbulence — one of the great unsolved problems of classical physics.
The big idea
Turbulence — the chaos of real fluids — is still not fully understood.
Think about it
Why does smoke rise in a smooth ribbon at first, then suddenly break into swirling chaos?
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