Perception of Pressure: at night vs in the morning

[greatunclebill]

the pressure itself is actually pretty low. it is measured as cm/h20. for instance 10 is the amount of pressure it takes to raise a column of water 10 cm. so as you can see the difference between the top and bottom of the scale is not that great. i think in terms of PSI it would all be in the 2 range someplace.

Let's see, what's the easiest way to do this calculation? Scuba divers learn that a depth of 10.3 meters (34 ft) is what it takes to increase the pressure by one atmosphere, which is about 15 psi.

So, let's see, 10 cm is about one hundred times smaller than 10.3 meters. If we make 15 psi one hundred times smaller we get 0.15 psi. That's not anywhere near enough to unflatten a flat tire, in fact, it wouldn't even blow up a balloon, would it?

But it's enough to keep our airways open while we sleep. Great Uncle, it's a miracle! I can't imagine how horrible my life would be without it.

i see it coming. somebody here is going to stick a balloon on the end of their machine to find out and probably will post a picture. who is it going to be? LOL........

i always thought the old first generation remstar would make a good aquarium pump if it could be stepped down to little hose.

[CHanlon]

the pressure itself is actually pretty low. it is measured as cm/h20. for instance 10 is the amount of pressure it takes to raise a column of water 10 cm. so as you can see the difference between the top and bottom of the scale is not that great. i think in terms of PSI it would all be in the 2 range someplace.

Let's see, what's the easiest way to do this calculation? Scuba divers learn that a depth of 10.3 meters (34 ft) is what it takes to increase the pressure by one atmosphere, which is about 15 psi.

So, let's see, 10 cm is about one hundred times smaller than 10.3 meters. If we make 15 psi one hundred times smaller we get 0.15 psi. That's not anywhere near enough to unflatten a flat tire, in fact, it wouldn't even blow up a balloon, would it?

But it's enough to keep our airways open while we sleep. Great Uncle, it's a miracle! I can't imagine how horrible my life would be without it.

The specific formula is:

cm h2o / 70.38 = psi

So... using my 95th percentile:

16.5 cm h2o / 70.38 = 0.23444 PSI

Or for your example:

10 cm h2o / 70.38 = 0.14208 PSI

So - you were pretty darned close... but high. :-)

[hippipdip]

Thanks for the feedback! Was just paranoid not knowing what to expect.

[Cutter]

Thanks for the feedback! Was just paranoid not knowing what to expect.

You're not paranoid, if they really are out to get you.

[PaulaO2]

I'm not paranoid. It's just a nasty rumor spread by those people out to get me.

[Sleepster]

Or for your example:

10 cm h2o / 70.38 = 0.14208 PSI

So - you were pretty darned close... but high. :-)

Well, I was just doing approximate calculation.

According to Wikipedia, it's 0.14223 psi.

This assumes, again according to Wikipedia, the water used for calibration is at its maximum density, which occurs at a temperature of approximately 4 deg C.

Regardless, if we adhere to those basic rules of the proper use of significant figures (we all aced that introductory physics course in college, right?) we have to round to 0.14 psi.

Now, let's see here, in my original calculation I said that we had to make 15 psi one hundred times smaller. But if I don't make that approximation, I would instead make 14.7 psi (that's more precisely equal to one atmosphere) 103 times smaller (because 10.3 meters is 103 times bigger than 10 cm).

14.7 psi / 103 = 0.14 psi.

And all this bother just to get Great Uncle Bill to try blowing up a balloon with his old CPAP machine.