pressure question

[Unlearner]

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why is the pressure lower in high altitude areas compared to sea level areas? does this have anything to do with the fact that there's less oxygen in high altitude areas?

 

[kwokkit]

This is just my way of thinking about it, but P = F / A = mg / A so P is directly proportional to F given constant g and A. Pretend you're standing at sea level, and there is a big column of air (say with mass X) sitting on your head that extends all the way up to the earth's atmosphere. When you climb up on Mount Everest, you have a a smaller column of air on your head (say with mass (X - Y), where Y is the difference between sea level and Everest) so pressure, in the sense of what's "on your head", is lower. Let me know if that makes sense.

 

[Bernoull]

This is just my way of thinking about it, but P = F / A = mg / A so P is directly proportional to F given constant g and A. Pretend you're standing at sea level, and there is a big column of air (say with mass X) sitting on your head that extends all the way up to the earth's atmosphere. When you climb up on Mount Everest, you have a a smaller column of air on your head (say with mass (X - Y), where Y is the difference between sea level and Everest) so pressure, in the sense of what's "on your head", is lower. Let me know if that makes sense.

kwokkit is exactly right.

Air is a fluid and fluid pressure, P = pgh where p=denstiy, g=gravitational acceleration (10m/s^2) and h=height (say from ground)
p&g are constant for different altitudes so P varies proportionally with h (P~h)!! The same is true for liquid, P varies with depth..

 

[EyEnStein 07]

The two previous posts basically got it, but here is just something to think about. Since we know fluids are gasses and liquids...consider what happens in a liquid.

If your in a pool or ocean that is very deep...its very difficult to go deep into the water because the pressure on your head (going down into the water) is much higher than the pressure on your feet because of the displacement of the water (refer to the formula that has delta x in it)..so thats why you could suffer ear damage and its very difficult to survive very deep in water.
(fish dont have this problem because they have gills) Also even 10 feet deep pools can potentially be dangerous, and it takes a lot of skill to go very deep i know theres like some limit i think 32 feet or something i forget though.

But in Air its different as kwokkit explains, but remmber we take in that air so we dont feel pressure.

 

[Unlearner]

bernoull,
you said pressure proportionally varies with height, if that's the case, it contradicts my original question, which was that the higher your go up (high altitude), LESS the pressure. i'm really confused now.

 

[Bernoull]

bernoull,
you said pressure proportionally varies with height, if that's the case, it contradicts my original question, which was that the higher your go up (high altitude), LESS the pressure. i'm really confused now.

I'm sorry for the confusing, I can see how the height can confuse, let me clarify...

Hydrostatic Pressure, which is what we are talking about here is given by
P=pgy

p=denstiy, g=gravitational acceleration (10m/s^2) and y=distance from fluid surface

If you have an aquarium, y is measured from the surface = depth basically.
For the atmosphere, its thickness is ~ 100km from the ground to outer space.. so you measure y from space. From space to the ground is 100km, height of everest is ~ 9km, therefore from space to everest is ~ 91km.

Having said all this, let find ground pressure and pressure at Everest's summit.

1. Ground: P=pgy= 100pg
2. Everest: P= 91pg

Pressure difference = 9pg.

In my first post I said P=pgh, what I failed to mention is that h is the difference between y1 & y2 (ground and everest)

So P=pgh = pg (100-91) = 9pg

In other words, h is the height/depth difference b/t 2 points and y if height/depth from fluid surface... As long as u calculate h or y correctly, you get da same result..

I'm hope ur less confused now..

 

[TheBoondocks]

I'm sorry for the confusing, I can see how the height can confuse, let me clarify...

Hydrostatic Pressure, which is what we are talking about here is given by
P=pgy

p=denstiy, g=gravitational acceleration (10m/s^2) and y=distance from fluid surface

If you have an aquarium, y is measured from the surface = depth basically.
For the atmosphere, its thickness is ~ 100km from the ground to outer space.. so you measure y from space. From space to the ground is 100km, height of everest is ~ 9km, therefore from space to everest is ~ 91km.

Having said all this, let find ground pressure and pressure at Everest's summit.

1. Ground: P=pgy= 100pg
2. Everest: P= 91pg

Pressure difference = 9pg.

In my first post I said P=pgh, what I failed to mention is that h is the difference between y1 & y2 (ground and everest)

So P=pgh = pg (100-91) = 9pg

In other words, h is the height/depth difference b/t 2 points and y if height/depth from fluid surface... As long as u calculate h or y correctly, you get da same result..

I'm hope ur less confused now..

Bernoull was correct. As you get higher altitude, the Y (column of air) decreases so this is why there is less pressure above.

 

[Bernoull]

Bernoull was correct. As you get higher altitude, the Y (column of air) decreases so this is why there is less pressure above.

After all this explanation I missed a AAMC question on pressure, da formula was P=pgH wat a B@$%$!!!!

Talk about irony, I overthought da problem but it turned out to be a simple pressure problem!!

 

[FutureInternist]

does this have anything to do with the fact that there's less oxygen in high altitude areas?

Keep in mind that ALL the gases decrease by the same percentage the higher you go. So, at Mt. Everest, N2 is still 75%, O2 is still 21% etc. The reason you can't breathe up there is that 21% of a small number (decreased pressure) is a very small number & hence not enough gradient to get the air in.

 

[Unlearner]

Thanks!!!