The other way to think about it is divergence is the source rate, it is the amount of fluid that is being inserted into the system, that is being pumped into the system per unit time per unit area.
If you were thinking of a velocity field, that would measure how much fluid is passing through the curve in unit time.
想象一个速度场,它能够度量,单位时间内流体的量。
3
He sketched devices to hold an iPad in a hospital bed. He designed new fluid monitors and X-ray equipment. He redrew that not-quite-special-enough hospital unit.