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When they define curl, they say it is a measure of "infinitesimal rotation", or "rotation per area".

What does that mean? Does it mean they measure how much something goes around in an infinitesimal point (which makes no sense), kind of like a whirlwind shrunk down? Or do they mean its the measure of how much something changes its direction, or "bends", at any point?

Second, can you guys give me an intuitive explanation for the following formula?

"The k-component of the curl of a vector field F = M*i + N*j at the point (x,y) is the scalar:

(Curl F)*k = ∂N/∂x - ∂M/∂y"

I sense that this formula represents how much the M and N components change direction, ie how much they bend, but I cannot get it down on paper..

Thanks for any help

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# Define curl rotation per area

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