Why do we not feel the effects of Atmospheric Pressure?

[Brandon Snider]

Given that I am in a second semester general chemistry course, atmospheric pressure has been discussed. I was wondering why we do not feel the effects of the atmosphere's intense pressure?

 

 

Following this:

 

http://suite101.com/article/weight-of-earths-atmosphere-a56021

 

and a previous calculation that I did on my own, the atmosphereic pressure is actually rather high (in terms of pounds.)

 

Why do we not feel this? I understand that, given evolutionary theory, our bodies may have adapted to this standard pressure, but I feel as though there may be a rather large disparity between atmospheric pressure at the coast and pressure at 3,333 ft. Given that the pressure is high in terms of pounds (being about 14.7 PSI) why do we not feel the change? I feel like we should notice having more than 14 pounds of pressure off of our bodies.

 

 

Sorry if this question seems elementary or stupid.

 

Thanks

[John Cuthber]

There are two parts to the reason.

Firstly the air inside us is at practically the same pressure as the air outside us. So we are being blown out as much as we are being squashed in.

Secondly the things we are made of are not very compressible. Increasing the pressure on water by 14.7 PSI only reduces the volume by about 50 parts in a million.

[D H]

You're looking at pressure the wrong way.

 

Imagine building a house of cards with a roof comprising one card. Now put a weight on top of that roof. One pound? Good luck. 128.6 pounds? Not a chance. The roof is not bearing a load of 128.6 pounds (2.5 inches × 3.5 inches × 14.7 psi).

 

Pressure doesn't work that way. It acts on every surface. It acts on the front and back of each of those cards in that house of cards. The net force on each card is near zero.

 

What pressure does is to make us lighter. Imagine suiting up in a vacuum suit, weighing your self in vacuum, and then weighing yourself again at STP. The latter measurement will be a tiny bit less than the first. The same thing happens with balloons filled with helium. A helium filled balloon will fall in vacuum. They rise in air because of buoyancy.

 

You can feel pressure if your body is not in equilibrium with the surrounding air. This happens if you drive down a mountain too fast; you have to pop your ears. It's also a big problem with diving underwater because all that's needed to be at twice atmospheric pressure is to dive down to 33 feet. Come up too fast and you'll feel a good deal of pain, and possibly sustain some damage. Come up slowly and your internal pressure will have time to keep pace with the changes in pressure.

Edited January 29, 2013 by D H

[Brandon Snider]

You're looking at pressure the wrong way.

 

Imagine building a house of cards with a roof comprising one card. Now put a weight on top of that roof. One pound? Good luck. 128.6 pounds? Not a chance. The roof is not bearing a load of 128.6 pounds (2.5 inches × 3.5 inches × 14.7 psi).

 

Pressure doesn't work that way. It acts on every surface. It acts on the front and back of each of those cards in that house of cards. The net force on each card is near zero.

 

What pressure does is to make us lighter. Imagine suiting up in a vacuum suit, weighing your self in vacuum, and then weighing yourself again at STP. The latter measurement will be a tiny bit less than the first. The same thing happens with balloons filled with helium. A helium filled balloon will fall in vacuum. They rise in air because of buoyancy.

 

You can feel pressure if your body is not in equilibrium with the surrounding air. This happens if you drive down a mountain too fast; you have to pop your ears. It's a big problem with diving because all that's needed to be at twice atmospheric pressure is to dive down to 33 feet. Come up too fast and you'll feel a good deal of pain, and possibly sustain some damage. Come up slowly and your internal pressure will have time to keep pace with the changes in pressure.

This may be a bad statement, but I'm almost curious to find a way to drop 33 feet quickly to experience this... Live in the mountains at the moment so...EDIT: Also, how much pain and damage are we talking? Not wanting to kill myself. Also, really appreciate both answers. They are really insightful.

 

Edit: Also, D H, would you mind explaining what you mean by pressure doesn't work that way? What I am confused about is the fact that Gravity should be causing atmospheric pressure. It is one thing to assume that there is no gravity, and that the pressure inside of and outside of a system are equal, but why does pressure make us lighter if (our internal pressure = environmental pressure) and then throw atmospheric pressure caused by gravity into the mix. I'm sorry I'm just a little bit confused because the way that I understood atmospheric pressure is that gravity pulls the mass of atmospheric gasses towards earth.

 

Sorry if my intent/question in ^ that wall of text isn't very clear.

Edited December 11, 2012 by Brandon Snider

[D H]

This may be a bad statement, but I'm almost curious to find a way to dropp 33 feet quickly to experience this.

That 33 feet is in water, not air. I said "It's a big problem with diving because all that's needed to be at twice atmospheric pressure is to dive down to 33 feet." Diving, as in diving underwater.

[Brandon Snider]

That 33 feet is in water, not air. I said "It's a big problem with diving because all that's needed to be at twice atmospheric pressure is to dive down to 33 feet." Diving, as in diving underwater.

Oops. Sorry. Didn't read carefully. Thought you said "driving." My mistake.

[efzauner]

This may be a bad statement, but I'm almost curious to find a way to drop 33 feet quickly to experience this... Live in the mountains at the moment so...EDIT: Also, how much pain and damage are we talking? Not wanting to kill myself. Also, really appreciate both answers. They are really insightful.

 

Edit: Also, D H, would you mind explaining what you mean by pressure doesn't work that way? What I am confused about is the fact that Gravity should be causing atmospheric pressure. It is one thing to assume that there is no gravity, and that the pressure inside of and outside of a system are equal, but why does pressure make us lighter if (our internal pressure = environmental pressure) and then throw atmospheric pressure caused by gravity into the mix. I'm sorry I'm just a little bit confused because the way that I understood atmospheric pressure is that gravity pulls the mass of atmospheric gasses towards earth.

 

Sorry if my intent/question in ^ that wall of text isn't very clear.

 

You just have to go to a public swimming pool and dive to the bottom of the deep end to feel the pressure on your ears! The reverse can also happen. A scuba diver who takes a deep breath and fills his lungs on the bottom of the pool, and goes to the surface with out exhaling can suffer an air embolism (burst lung and air entering the blood stream) due to the pressure of expanding air in his lungs.

 

Yes the earth's gravity causes our atmosphere to be pulled and stay on the earth otherwise it would dissapear like the moon or mars! The weight of a one inch square column of air at sea level is 14.7 lbs! As you go higher there is less air above you and therefore the pressure per square inch is less.

 

Pressure does not make us lighter. It is the boyancy of the air that makes us lighter. This is called Boyle's law. If you weigh yourself on a scale, you will measure your mass minus the mass of the volume of air that your body displaces. This difference is trivial when we weigh ourselves but may not be trivial in precise measurements or scientific experiments. This is also how boats and hot air or helium balloons float. If the pressure is higher, then the mass of the air that your body displaces is also higher and you will be boyed upward a tiny bit more! But this is such a small unnoticeable amount.

 

As far as feeling the effects of pressure, even if you dive very deeply the pressure does not affect the liquid or solid parts of your body but only air cavities such as lungs or sinuses and ears, or air caught in your intestines. You can experience this also in a plane. I get sinus headaches in a plane!

Also when at higher altitudes, because of lower pressure, less oxygen gets pushed across the air/blood interface in our lungs and we have difficulty performing physicaly... we get tired! If you live at higher altitudes for a while, your body will compensate by producing more hemoglobin.

 

Hope this helps.

Edited January 8, 2013 by efzauner

[too-open-minded]

We don't necessarily feel the atmospheric pressure because of, well even if you go to a different elevation your not going very far in either distance of the threshold amount of pressure to support our bodies. Your not going to feel what your used to, although break the threshold and you notice or "feel" the pressure.

[Bignose]

Oops. Sorry. Didn't read carefully. Thought you said "driving." My mistake.

Don't feel bad, my brain did the exact same thing. I was thinking of when I drove across the Rocky Mountains, and did need to pop my ears frequently, but 33 feet seemed just a little low to me too

[ewmon]

There's an important word to apply here ... equilibrium. Everything around you experiences the same pressure (ie, equilibrium). If you bake one of those angel food "sponge" cakes, it's flimsy, and yet, it was created at 14.7 psi, so it's at equilibrium at that pressure. If you take your sponge cake to Bolivia's Altoplano region (~14,000 feet altitude), it would expand. Bake one there, and it will have a particular size, and bring both down to sea level, and the first one will return to its normal size, and the high-altitude one will shrivel. These are, of course, perfectly ideal sponge cakes.

[CaptainPanic]

Given that I am in a second semester general chemistry course, atmospheric pressure has been discussed. I was wondering why we do not feel the effects of the atmosphere's intense pressure?

We do feel it. We just don't notice it anymore.

 

Take a balloon. If you want to increase the pressure in the balloon, and you push on it with two hands, it does not work. The balloon just expands where you are not pressing. The only way to make the balloon smaller (other than letting the air out - that's cheating) is to have enough people, with enough hands to push on every surface of that balloon. Air pressure is just like that: it's pressing everywhere.

 

The only reason why the atmosphere cannot press us into something smaller is that our bodies are made up of liquids and solids, which cannot be compressed much. In a simplified way, we say that liquids and solids are "incompressible". And all the gases in our bodies, like in our lungs, is also at atmospheric pressure too.

[SamBridge]

Y

You can feel pressure if your body is not in equilibrium with the surrounding air. This happens if you drive down a mountain too fast; you have to pop your ears. It's a big problem with diving because all that's needed to be at twice atmospheric pressure is to dive down to 33 feet. Come up too fast and you'll feel a good deal of pain, and possibly sustain some damage. Come up slowly and your internal pressure will have time to keep pace with the changes in pressure.

 

 

I've done a lot of driving through and in and down mountains and sometimes a straight enough incline to go fast, and I'm pretty sure my ears popped sometimes but there was never any pain at all. What you're describing sounds like "the bends" which isn't in air, but in water, and it's because water is denser in air that changing pressure too fast would compress or uncompress the air in your body too quickly and it will damage joints and tissue sometimes enough to cripple you if you're not careful enough.

Edited January 26, 2013 by SamBridge

[Bignose]

I've done a lot of driving through and in and down mountains and sometimes a straight enough incline to go fast, and I'm pretty sure my ears popped sometimes but there was never any pain at all. What you're describing sounds like "the bends" which isn't in air, but in water, and it's because water is denser in air that changing pressure too fast would compress or uncompress the air in your body too quickly and it will damage joints and tissue sometimes enough to cripple you if you're not careful enough.

...and another person's brain just put the 'r' right into that word.

 

Don't feel bad, Sam, you're at least the 3rd one whose brain has done this them.

 

(p.s. D H did write 'diving', not 'driving')

[D H]

Don't feel bad, Sam, you're at least the 3rd one whose brain has done this them.

Which means it's my fault for not writing clearly rather than the fault of all you readers for misreading what I wrote.

 

Sorry for any confusion I might have caused.