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Altitude and air density 
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#1
Feb613, 09:35 AM

P: 645

As we go higher up a mountain, the air pressure decreases. But why would that cause the air density to decrease? Since pressure is hpg, so if h decreases pressure decreases but what causes the air density to decrease as well?
Thanks for the help :) 


#2
Feb613, 09:40 AM

P: 4,232

Gases are compressible. More pressure means they are compressed into a smaller volume. Liquids not so much. Water has about the same density in a column.



#3
Feb613, 10:09 AM

P: 645

But then again now with only one formula, P=hpg now that h and p decrease so the pressure will decrease disproportionately? 


#4
Feb613, 10:10 AM

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Thanks
PF Gold
P: 6,743

Altitude and air density
It's a direct consequence of PV = nRT.



#5
Feb613, 10:21 AM

P: 645

Thanks 


#6
Feb613, 10:46 AM

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P: 5,196

P = nkT Where n = N/V is the number of particles per unit volume. Multiply n by m, the mass per particle, and you get the mass per unit volume (aka density) rho. Hence n = rho/m and the ideal gas law becomes P = (rho/m)kT For air, there is more than one type of particle so m is a weighted average of the masses of the different molecules. 


#7
Feb613, 11:14 AM

P: 645




#8
Feb613, 12:13 PM

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P: 5,196




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