Is the Upthrust Equation for Fully Submerged Objects Incorrect?

[Olivia197]

Please may somebody explain why this equation for the pressure at the bottom of a fully submerged object is wrong (assuming it is a cube). Thank you!

Pressure = ( density of the fluid x h[1] x g ) + ( density of the cube x (h[2] - h[1] ) x g)

 

[Herman Trivilino]

What makes you think it's wrong?

 

[mfb]

Why do you expect it to be right?
How do you imagine the pressure distribution close to the edge of the object? Jumping?

Is this a static situation? If you include dynamics, things get more complicated.

 

[Olivia197]

What makes you think it's wrong?

Well, in my textbook it says that the pressure is the density of the liquid x h [2] x g.

 

[Olivia197]

Why do you expect it to be right?
How do you imagine the pressure distribution close to the edge of the object? Jumping?

Is this a static situation? If you include dynamics, things get more complicated.

Sorry I am not quite sure what you mean!

 

[Herman Trivilino]

Well, in my textbook it says that the pressure is the density of the liquid x h [2] x g.

Then anything different from that would be wrong. It seems to me that you've answered your own question.

Please may somebody explain why this equation for the pressure at the bottom of a fully submerged object is wrong

.

 

[mfb]

Sorry I am not quite sure what you mean!

Well, reduce it to the first question: why do you expect your expression to be right?

 

[sophiecentaur]

Well, reduce it to the first question: why do you expect your expression to be right?

Could (s)he express, in words, what that equation is describing? That may help with the understanding.

 

[russ_watters]

That equation might work -- is the object neutrally, positively or negatively buoyant? Is it moving or constrained not to move?

 

[sophiecentaur]

That equation might work -- is the object neutrally, positively or negatively buoyant? Is it moving or constrained not to move?

I see where you are going with this but the hydrostatic pressure is not really affected by the density of the object (or the object at all). The pressure at the bottom face is due to the column of fluid, rather than the object (unless there is some extra factor involved that we haven't been told about).

 

[russ_watters]

I see where you are going with this but the hydrostatic pressure is not really affected by the density of the object (or the object at all). The pressure at the bottom face is due to the column of fluid, rather than the object (unless there is some extra factor involved that we haven't been told about).

The answer to my question is "other factors" and will actually push the solution toward the normal hydrostatic pressure equation when the OP realizes the impact of the constraints the answer adds.