# Buoyancy, upthrust

1. Feb 13, 2015

### Suraj M

1. The problem statement, all variables and given/known data
A solid is completely immersed in a liquid. The force exerted by the liquid on the solid will(more than one right)
(a)increase if it is pushed deeper inside the liquid.
(b)change if its orientation is changed
(c)decrease if it is taken partially out of the liquid
(d)be in the vertically upward direction

2. Relevant equations

U=Vdlg
3. The attempt at a solution
Option C and D are true i got that, and the answers also say that the answer is C and D.
But why is Option A not true, the upthrust does increase when the solid is pushed down, right??
I just want to be sure. Thank you in advance

2. Feb 13, 2015

### Bystander

How do you propose that the force should increase?

3. Feb 13, 2015

### Suraj M

With depth there would be increase in pressure, as liquids have a higher compressibility factor than solids. Hence the density of the liquid would increase at a higher rate as compared to the solid. So the upthrust should increase, right?

4. Feb 13, 2015

### Bystander

Is this statement true for all possible liquid-solid pairs?

5. Feb 13, 2015

### Suraj M

I'm not sure. By you're tone, i guess it isn't true for all.
Could you give an example of a pair where this wouldn't be true‽

6. Feb 13, 2015

### Bystander

Mercury ( ~ 3 ppm/atm) and let's say hard rubber.

7. Feb 13, 2015

### Suraj M

wouldn't rubber float in mercury?

8. Feb 13, 2015

### Bystander

You could be using rubber coated uranium bricks; you're not constrained by liquid and solid densities in any way in the problem statement, you're merely calculating net buoyancy forces.

9. Feb 13, 2015

### Suraj M

oh ok. thank you!

Last edited: Feb 13, 2015