Vector Integral Calculus: Feynman's Physics Explained

Feynman Vol II9-10

Differential laws describe what happens at each point; integral laws describe the overall behavior. Gauss's theorem says the total flux of a field flowing out of a closed surface equals the sum of all the little sources (the divergence) inside it. Stokes' theorem is the partner statement: the total circulation around a closed loop equals the sum of all the little swirls (the curl) on the surface it encloses.

The big idea

What flows out of a surface equals the sources packed inside it.

Think about it

If you know how much water leaves a closed bag's surface, what does that tell you about taps or drains hidden inside?

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