PSI & Buoyancy: Container Air Pressure Effect on Sink/Float

In summary, Archimedes' principle states that the force of buoyancy is proportional to the volume displaced by the object, and that a greater pressure will result in a greater buoyant force.
  • #1
XZ923
136
63
A question about PSI and buoyancy. How does the air pressure of a container effect whether the container will sink or float? For instance, if two containers of the same mass and area (and the mass of the container itself is negligible), one container is filled with 10psi of air and the other 100psi, then weights are attached to them, will it take 10 times as much weight to sink the first container as the second or 1/10 the weight?
 
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  • #2
Have you heard of Archimedes principle?
 
  • #3
Yes I have this leads me to believe that the 100 psi container would sink quicker due to the increased density but it seems counter-intuitive, wouldn't a balloon with high pressure take more effort to sink than a balloon of equal area but with a much lower pressure?

I have the feeling I'm missing something blindingly obvious here and I guess I'm fishing for my own "Eureka" moment.
 
  • #4
The volume of the fluid displaced by the object is what determines the buoyant force. Suppose you had two equal volume containers but one had feathers and the other had lead. The buoyant force on each container would be equal if they were fully submerged in a fluid, but the force of gravity is certainly different.

I think the balloon is perhaps a potentially confusing example because the higher pressure will result in a greater volume and thus in a greater buoyant force. Imagine that the balloon is stuffed into the container and not allowed to expand. Would a greater pressure inside the balloon in this case make it float more readily according to Archimedes?
 
  • #5
XZ923 said:
Yes I have this leads me to believe that the 100 psi container would sink quicker due to the increased density but it seems counter-intuitive, wouldn't a balloon with high pressure take more effort to sink than a balloon of equal area but with a much lower pressure?

I have the feeling I'm missing something blindingly obvious here and I guess I'm fishing for my own "Eureka" moment.

I think maybe your confusion comes from the fact that usually a balloon with higher pressure will displace more water, and because of that it would rise faster. But one of your constraints was that the volume of the balloons are the same (which makes them rather un-balloon-like, and rather more like solid spheres), in which case really only the total weight of the object matters.
 
  • #6
rumborak said:
I think maybe your confusion comes from the fact that usually a balloon with higher pressure will displace more water, and because of that it would rise faster. But one of your constraints was that the volume of the balloons are the same (which makes them rather un-balloon-like, and rather more like solid spheres), in which case really only the total weight of the object matters.

A balloon was probably a bad example; I was attempting to highlight the fact that I was referring to how air pressure relates to buoyancy.

Let me redefine: If two identical static, sealed containers are placed in a tank, with one pressurized to 10psi of air and the other to 100psi, the 100psi container would have ten times the buoyancy, since to reach ten times the pressure in containers with identical area would require the volume of air to be 10 times higher. Is this correct?
 
  • #7
Nope, that is not correct.

The real question is, do you fully understand Archimedes' principle? Because this right now seems like a battle between your intuition and Archimedes.
 
  • #8
rumborak said:
Nope, that is not correct.

The real question is, do you fully understand Archimedes' principle? Because this right now seems like a battle between your intuition and Archimedes.
My guess would be that Archimedes is correct...

Would it be the opposite; the 100psi container has less buoyancy due to the greater density?
 
  • #9
Yup. All other things equal, the container with more pressure contains more molecules, and thus it is heavier.
 
  • #10
rumborak said:
Yup. All other things equal, the container with more pressure contains more molecules, and thus it is heavier.
That's what I was thinking at first but for some reason it just didn't seem right. For some reason I was thinking that a highly pressureized object would be harder to sink than a less-pressurized one.

Anyway thanks for the insight. I'm going back to the garage; motors make my brain hurt less.
 

1. How does air pressure affect the buoyancy of objects?

Air pressure plays a critical role in determining the buoyancy of objects. As air pressure increases, the density of the air also increases, making it harder for objects to float. This is because the air exerts a downward force on the surface of the water, causing it to compress and become denser. This increased density creates an upward buoyant force on objects, making them more likely to float.

2. What is PSI and how does it relate to buoyancy?

PSI (pounds per square inch) is a unit of measurement commonly used to measure air pressure. It is often used to measure the pressure of the air above and below the surface of the water. As PSI increases, so does the density of the air, ultimately affecting the buoyancy of objects. A higher PSI means a higher air density, resulting in a greater upward buoyant force on objects.

3. How does the shape of a container affect the buoyancy of objects?

The shape of a container can greatly impact the buoyancy of objects. A wide and shallow container will have a larger surface area, resulting in a greater amount of air being compressed. This will create a larger upward buoyant force on objects compared to a tall and narrow container with a smaller surface area. Additionally, the shape of the container can also affect the distribution of air pressure, further impacting the buoyancy of objects.

4. Can the temperature of the air affect the buoyancy of objects?

Yes, the temperature of the air can affect the buoyancy of objects. As air temperature increases, the air molecules move faster and spread out, resulting in a decrease in air density. This decrease in density will ultimately lead to a decrease in the upward buoyant force on objects, making them less likely to float. Conversely, colder air will have a higher density, resulting in a greater upward buoyant force on objects.

5. How does the weight of an object affect its ability to float?

The weight of an object is directly related to its buoyancy. Objects that are heavier than the water they displace will sink, while objects that are lighter than the water they displace will float. The upward buoyant force on an object must be greater than its weight for it to float. This is why denser objects, such as rocks, sink while less dense objects, such as wood, float.

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