## shivam_bhalla 3 years ago See the question in diagram My question is what is the pressure felt by the wall Wait for diagram

1. shivam_bhalla

|dw:1335593779148:dw| P-->Pressure applied on wall of cylinder Assume one side of the cylinder is filled with liquid as in figure i) Does P vary with depth of cylinder ii)How do you get P?

2. shivam_bhalla

3. mos1635

are we looking for pressure or total force???

@shivam_bhalla Pressure increases linearly with depth, the exact relation being P=pgh. In this problem, the density is same and gravitational constant is also same. The only thing that varies the pressure down the wall is how deep we go. From the figure, the wall is h units high and 2r units in width. At the top of the wall, the pressure is 0 (p*g*0) and at the bottom it is pgh. Since it increases linearly, we can use the average value of pressure that is pgh/2 as the pressure on the entire wall. The area of the wall is 2rh. So the force on the wall is (pgh/2)*(2rh), this is pressure times area. Alternately, you can divide the wall into horizontal strips of height dh and length 2r. the force on a particular segment at a depth of h is 2rpghdh. You can find the total force by integrating this expression from 0 to H. I wouldn't recommend this though because it is a longer method. Remember in general that for a quantity changing linearly, you can use the average value to represent the quantity at any instance. We do this in constantly accelerated motion where u is initial velocity and v is final velocity. We can compute distance by (u+v)/2 * time.

5. shivam_bhalla

At the top of the wall, the pressure is 0 (p*g*0) -->how, what about surface tension??

6. shivam_bhalla

We have the force, but the area would be negligigble? Am I right @Aditya790

7. shivam_bhalla

And so pressure due to surface tension-->Almost absent

@shivam_bhalla Yes. Compared to the pressure, surface tension is a very small value. At 20 degrees centigrade, the force due to suface tension is on the top is 0.0727*2r newton, which is very slight. Nice point though, I never considered surface tension in such a case. Since the surface tension acts only on the top, it causes a torque inward. To weak to cause a steel/glass vessal to break. But if you pour water into a non-rigid container like a plastic cover, the cover kind of closes up on the top and the body of the cover becomes spherical in shape (sphere has minimum surface area for a given volume) as water tries to minimise its surface area. Thanks for bringing my attention to it.

9. shivam_bhalla

@Aditya790 , You are a computer or what :P . Great work :)