Here's a Hint:
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In addition to coining the word "hydrodynamics," Daniel laid out the basic principles of the new science, applying Newton's basic laws to simplified cases of fluid dynamics. Out of this work came Bernoulli's Principle (or Law), which Euler helped express as a mathematical equation known as Bernoulli's Equation. What Bernoulli found boiled down to this: when a fluid is moving-through a pipe or conduit, or simply over any surface-it exerts pressure in all directions: against anything that is in the way of its flow, as well as against any surface it touches. For example, as water flows through a garden hose, you can feel the pressure of the water against the inner wall of the hose if you try to squeeze the hose. Now, if the fluid is non-compressible (meaning it can't he squeezed into a smaller volume, which is true of water, in most ordinary circumstances), and if there is no change in the amount of fluid flowing (meaning nothing is leaking out or coming in), then the faster the fluid is flowing, the lower its pressure against the surface it's flowing over will be.
That means that when you pinch the garden hose slightly in the middle and the water keeps coming out of the end at the same rate, then the water must be travelling through the pinched portion a little faster (since the same amount of water is passing through that section of the hose as before). Our intuition is that faster water exerts greater pressure (and it does, but only in the direction of the flow), but the pressure of the faster water against the wall of the hose (which is perpendicular to the direction of the flow) is less-a total surprise.
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