Can External Pressure Increase the Pressure Inside a Sealed Sphere?

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In summary: Pressure is force per area.In summary, the conversation discusses a thought experiment involving two airtight containers filled with gas, both having the same volume, temperature, and pressure. The question is whether adding a heavy weight on one of the containers would change the pressure inside. The consensus is that, assuming no deformation occurs, the pressure inside the container would not change since only a change in volume, amount of substance, or temperature can affect pressure.
  • #1
Ofey
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I came across this thought experiment, and I even think I have a solution for it, but my book insists that I am wrong.

Consider a completely airtight shere, filled with air. Applying any sort of pressure outside the sphere surely cannot increase the airpressure inside the sphere? (assuming that the volume of the sphere is constant). As I see it, only a change of volume, amount of substance or temperature can change the pressure of the air. I believe that the book incorporates the method of simply adding pressures together. This works fine when asking for a total pressure at a certain depth at sea (total pressure equals the airpressure and the hydrostatic pressure), but surely it cannot work for the "sphere problem"

Thoughts?
 
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  • #2
Hello, and welcome to PF.

I don't really follow your question. I agree with the statement that "only a change of volume, amount of substance or temperature can change the pressure of the air" - PV = nRT!

Does the problem state that the sphere's volume doesn't change, or that its made of Kryptonite (near infinite elasticity)? Can you provide a sketch of the problem?
 
  • #3
Is this a gage pressure vs atmospheric pressure issue? The last sentence implies that...
 
  • #4
russ_watters said:
Is this a gage pressure vs atmospheric pressure issue? The last sentence implies that...

Sorry for being unclear, maybe this sketch helps.

We have two airtight containers, filled with a gas. Both have the same volume, same temperature, and the pressure inside/outside the containers are equal. They even have exactly the same amount of substance. (In other words we have to identical containers). We now place a (very) heavy weight on the second container. What is the new pressure inside the container? Is it larger because we have added pressure on the surface of the container or is it exactly the same as before? (Assume that the second container doesn't undergo any deforamtion as weight is added on it, since this would imply that its volume would change and hence the pressure would change).

http://img261.imageshack.us/my.php?image=pressurerh5.png
 
  • #5
http://img261.imageshack.us/my.php?image=pressurerh5.png
 
  • #6
Ofey said:
Sorry for being unclear, maybe this sketch helps.

We have two airtight containers, filled with a gas. Both have the same volume, same temperature, and the pressure inside/outside the containers are equal. They even have exactly the same amount of substance. (In other words we have to identical containers). We now place a (very) heavy weight on the second container. What is the new pressure inside the container? Is it larger because we have added pressure on the surface of the container or is it exactly the same as before? (Assume that the second container doesn't undergo any deforamtion as weight is added on it, since this would imply that its volume would change and hence the pressure would change).

http://img261.imageshack.us/my.php?image=pressurerh5.png

I can't see your sketch, however, based on your description and assumption that no deformation occurs (and that it is a closed adiabatic system), the pressure inside the container would not change.

CS
 
  • #7
As I see it, only a change of volume, amount of substance or temperature can change the pressure of the air.

You are correct and so are the above replies.
 

Related to Can External Pressure Increase the Pressure Inside a Sealed Sphere?

1. What is pressure and how is it measured?

Pressure is defined as the amount of force applied over a given area. It is measured in units of force divided by units of area, such as pounds per square inch (psi) or pascals (Pa).

2. What factors affect pressure?

Pressure can be affected by several factors, including the amount of force applied, the area over which the force is applied, and the density of the material. Additionally, changes in temperature and altitude can also impact pressure.

3. How does pressure impact the behavior of gases and liquids?

In gases and liquids, pressure plays a critical role in determining their behavior. An increase in pressure can cause gases to become more dense and liquids to become more viscous. It can also lead to changes in temperature and volume.

4. What is the difference between absolute pressure and gauge pressure?

Absolute pressure is measured relative to a perfect vacuum, while gauge pressure is measured relative to atmospheric pressure. This means that absolute pressure includes the pressure exerted by the atmosphere, while gauge pressure only measures the pressure above atmospheric pressure.

5. How is pressure used in everyday life?

Pressure is used in a variety of ways in everyday life. For example, it is used in tire gauges to measure the pressure of car tires, in barometers to measure atmospheric pressure, and in blood pressure monitors to measure blood pressure in the body.

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