# Expression for the change in water height in a tank

## The Attempt at a Solution

There is solved problem on change in water height with respect to time. I understand it but there is the b part of the question. It asks that what's if the top of the tank is open to the atmosphere?

I think nothing would change but we would ignore the mass of the air in the calculation. So is it correct?

Thank you.

Source: Fluid Mechanics by Frank M. White

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## Answers and Replies

BvU
Homework Helper
First reading caused a bit of confusion - I try to fix it below...

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BvU
Homework Helper
Hello,
In a second round I spent some more time reading all of your post -- and it turns out I can skip a great deal. It also turns out I have to read the lower part first and then the upper part . In the context of the exercise the fluid flow in terms of the velocity is given. Tank open or closed has an effect on the pressure behaviour but with these givens that does not affect the answer. Just before the exercise begins, the author uses the word 'realistic'. To me that doesn't apply to the exercise: I wouldn't know what a one dimensional inlet is. And usually fluid flow is pressure dependent.

My post #2 is now a bit out-of-context, so I'll erase it ... in order not to look too stupid for casual readers like me

Hello,
In a second round I spent some more time reading all of your post -- and it turns out I can skip a great deal. It also turns out I have to read the lower part first and then the upper part . In the context of the exercise the fluid flow in terms of the velocity is given. Tank open or closed has an effect on the pressure behaviour but with these givens that does not affect the answer. Just before the exercise begins, the author uses the word 'realistic'. To me that doesn't apply to the exercise: I wouldn't know what a one dimensional inlet is. And usually fluid flow is pressure dependent.

My post #2 is now a bit out-of-context, so I'll erase it ... in order not to look too stupid for casual readers like me

Hello. I think author try to explain that the formula for conservation of flow rates is realistic. It doesn't directly said for the exercise but it is related to it as well.

It is very clear and easy to understand that the calculations never change when the top is open to the atmosphere. So why does author want to ask this?

I will continue to study background concepts related to this example such as one dimensional flow in this example.

Thank you.