Atmospheric Pressure and Mercury in a Test Tube

AI Thread Summary
The discussion revolves around understanding the behavior of mercury in a test tube under different atmospheric pressure scenarios. Participants suggest using a free body diagram (FBD) to analyze the forces acting on the mercury blob in each situation. The original poster seeks clarification on the specific lengths of mercury in two situations, questioning how atmospheric pressure influences these lengths. There is a consensus that atmospheric pressure plays a crucial role in holding the mercury in place, despite it being stationary in all cases. The need for a clearer understanding of the forces at play and their effects on mercury's position is emphasized.
yenhan10
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The problem statement



Recently I came across this problem and couldn't understand it.

I know that in situation 1, the length of the specific place will be decreased; In situation 2, it will be increased.

Can someone help me here? Thanks first!
 
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yenhan10 said:
The problem statement



Recently I came across this problem and couldn't understand it.

I know that in situation 1, the length of the specific place will be decreased; In situation 2, it will be increased.

Can someone help me here? Thanks first!

Welcome to the PF.

With problems like this, you need to draw a free body diagram (FBD). For each situation, draw the forces that are acting on the mercury blob.
 
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What holds the mercury in the specified locations in all the cases? Why the difference?
 
berkeman said:
Welcome to the PF.

With problems like this, you need to draw a free body diagram (FBD). For each situation, draw the forces that are acting on the mercury blob.

Hi do you mean this?


I need to know exactly what are the lengths for both specific situation...
 
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voko said:
What holds the mercury in the specified locations in all the cases? Why the difference?

Hi I'm not sure. I was given this problem in a practice. Maybe assuming there's an unknown gas inside? Situation 2 might be held by the atmospheric pressure? I have to find out the exact length covered by mercury.. Help!
 
Observe that in situations 1, 2 and 3, in the first picture, atmospheric pressure is always present on the open end of the tube, and pushes the mercury inward. What is its force?

But the mercury is stationary in all the cases. Why?
 
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