confused on pressure stuff

[AA|FCB|DOC]

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I was doing a problem on the velocity of the fluid that is coming out at the bottom of an open tank. Obviously we have to use bernoulli's equation. So at the the top of the tank I know that the pressure will just be atmospheric pressure, the velocity will be basically zero since it is not really moving, and the h in pgh will just be the height of the top of the tank from the bottom opening. Now at the bottom I know the height will be considered 0, but I do not understand why the pressure is just equal to atmospheric pressure? Should it not be atmospheric pressure PLUS the pressure at that depth? EK shows it as just atmospheric pressure and this makes no sense to me. any help would be appreciated.

 

[MedPR]

These types of problems consider the pressure as the fluid leaves the hole. In other words, when the fluid enters the atmosphere.

 

[AA|FCB|DOC]

Hmm that makes sense except for one problem i saw in EK. idk if you have it, but its problem 106 in the physics book, one of the in class problems (not 30 min exams). It says the point D one is at atmospheric pressure, which make sense like you said since its considered as outside, but the point C one it says is also at atmospheric pressure which to me seemed like it should be greater than atmospheric pressure.

 

[ouroboros39]

The fluid at point C will be moving at a faster rate, so it will have to have a lower pressure to compensate. The orange text on page 85 kind of offers a half decent explanation. I didnt look at the explanation, but I think the pressure at point C would depend on the speed of the fluid at that point, either way, though, it would be at lower pressure than point B.

 

[AA|FCB|DOC]

yea i agree that it would be lower, and i also thought it would be because of fluid movement. But i did not think it would be lower to the extent where its just atmospheric pressure. The diagram does explain except there is no point c 🙁