Atmospheric Pressure and Mercury in a Test Tube

In summary, the conversation is discussing a problem statement involving the behavior of mercury in different situations. The participants suggest drawing a free body diagram to understand the forces acting on the mercury blob. The conversation also includes a question about the role of atmospheric pressure and an assumption about an unknown gas. The main question is what holds the mercury in place in each situation, and the participants are seeking clarification on the exact length of mercury coverage.
  • #1
yenhan10
3
0
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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  • #2
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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  • #3
What holds the mercury in the specified locations in all the cases? Why the difference?
 
  • #4
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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  • #5
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!
 
  • #6
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?
 

Related to Atmospheric Pressure and Mercury in a Test Tube

1. What is atmospheric pressure?

Atmospheric pressure is the force per unit area exerted by the Earth's atmosphere on a given surface. It is caused by the weight of the air molecules above the surface and is measured in units of pressure, such as millibars or inches of mercury. On average, atmospheric pressure at sea level is about 14.7 pounds per square inch.

2. How does atmospheric pressure affect the behavior of gases?

The higher the atmospheric pressure, the more tightly packed the air molecules are. This means that gases will compress more easily under higher pressure. Conversely, under lower atmospheric pressure, gases will expand more and take up more space.

3. What is the relationship between atmospheric pressure and altitude?

As altitude increases, atmospheric pressure decreases. This is because there are fewer air molecules above a given surface at higher altitudes, resulting in lower pressure. For example, at the top of Mount Everest, the atmospheric pressure is only about one-third of what it is at sea level.

4. How is mercury used to measure atmospheric pressure?

Mercury is used in a tool called a barometer to measure atmospheric pressure. A barometer consists of a long glass tube filled with mercury and inverted into a dish of mercury. The atmospheric pressure pushes down on the surface of the mercury in the dish, causing it to rise into the tube. The height of the mercury column in the tube is a measure of the atmospheric pressure.

5. Can atmospheric pressure be affected by weather?

Yes, weather can have an impact on atmospheric pressure. High pressure systems typically bring clear, dry weather while low pressure systems are associated with clouds and precipitation. Changes in atmospheric pressure can also indicate impending weather changes, such as a drop in pressure before a storm.

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