# Buoyant force acting on an inverted glass in water

• MatinSAR
In summary, according to the information given in the question, the glass and the air inside it enter the water. As the glass goes down in the water, the pressure increases and the air inside the glass is compressed, resulting in a decrease in volume. This decrease in volume leads to a decrease in buoyancy force and force F, causing the object to move downwards at a constant speed. However, the question does not provide enough information to determine how force F should be applied. Additionally, the statement that the gas volume stops decreasing from time to time is incorrect, as the depth of the container is infinite and the reduction in volume will continue indefinitely.
MatinSAR said:
I appreciate your help. I didn't use PatmL/(L -δ) = Patm+ρg(h-δ) because
2nd degree equation was obtained ...

I have used the formula you suggested ...
What formula?

MatinSAR
erobz said:
I don't understand! I solved it as a quadratic. However, your result indicates that my quadratic must be factorable I believe?
Maybe I made a mistake ...

MatinSAR said:
Maybe I made a mistake ...
It plots identically to my solution?

MatinSAR
erobz said:
It plots identically to my solution?
Let me send you a picture of what I have done ...

erobz
erobz said:
It plots identically to my solution?
My mistake is here :

So to find delta we have to solve a quadratic equation ...

The question only asked about the increase and decrease of F force, I didn't want to waste your time at all... I'm sorry...
edit :

I have solved that quadratic equation ...

Last edited:
erobz
MatinSAR said:
My mistake is here :
View attachment 318768

So to find delta we have to solve a quadratic equation ...

The question only asked about the increase and decrease of F force, I didn't want to waste your time at all... I'm sorry...
edit :

View attachment 318770

I have solved that quadratic equation ...
What you did on accident the first time by omitting ##\delta## was actually a really good approximation for ##\delta \ll h##. For the parameters I used I couldn’t tell the apart.

MatinSAR
MatinSAR said:
My mistake is here :
View attachment 318768

So to find delta we have to solve a quadratic equation ...

The question only asked about the increase and decrease of F force, I didn't want to waste your time at all... I'm sorry...
edit :

View attachment 318770

I have solved that quadratic equation ...
I wanted you to explore it. It wasn’t a waste of my time at all!

MatinSAR
erobz said:
I wanted you to explore it. It wasn’t a waste of my time at all!
Thank you for your help and time ...

erobz

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