# 2 connected tubes filled with water, placing a stopper in one and raising the other, how can I determine pressure exerted onto the stopper?

If I have two 20ml test tubes connected at the base via a thinner flexible U-shape tube and I pour a set amount of water (40ml) into one test tube whilst both are at level height, the water equilibrates so that it is at the same level in each tube. If I then introduce a stopper to meet the surface of the water in one tube and raise the other open tube to a higher level of lets say 2cm, how can I determine the pressure exerted onto the stopper by the water as the system once again tries to reach equilibrium? I'm not sure what equations I need in order to work out everything that is going on in the system. I'm trying to mimic a certain pressure against the stopper but first need to understand what the current pressure is and what factors I am working with in order to change the height of the other tube to gain the pressure I am after. Below is a simple schematic of what I mean, any help to get me started would be great - thank you!

• Are you familiar with the equation $\Delta p=\rho g h$ Commented Jan 6, 2021 at 12:36
• Thank you - this makes sense, I thought it would be more complicated. Commented Jan 6, 2021 at 13:30

$$P=P_0+\rho g h$$
where $$P_0$$ is the atmospheric pressure.