Bernoulli’s Principle seems to say that increased flow velocity causes less pressure. This does make sense, since pressure takes energy and so does motion, so with a fixed amount of energy of course there’s a tradeoff. But in every example I can think of, the opposite seems to be true. If you put your thumb over a hose nozzle, the water goes faster and there’s also increased pressure on your thumb. The higher you turn the water flow, the faster the water flows and the stiffer the hose becomes. What am I missing?
In: Physics
Bernoullis Principal is basically conservation of mechanical energy for fluids. It should not be applied in a situation where the fluid is flowing through a long, narrow pipe, since viscosity (analogous to friction) is a dominating factor. It doesn’t help that, when learning about Bernoullis principal, fluid flowing through pipes is the go to example.
When fluid flows through a pipe, it experiences “head loss”, which is a decrease in the mechanical energy due to the viscosity/friction between the fluid and the walls of the pipe. All else being equal, the faster the fluid flows, the more head is lost. By putting your thumb over the end of the hose, you are forcing the fluid in the hose to flow slower overall, meaning it has more head when it reaches you, and thus greater pressure where you thumb is, and greater velocity where your thumb isn’t.
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