High building windows

  • Thread starter Gyroscope
  • Start date
  • #1

Homework Statement


This is one more problem I made to entertain myself.

I am at the highest floor of a building near a window. There is strong wind outside.
The pressure inside is approximately the atmospheric pressure, but outside it is less because the air is flowing, so by Bernoulli's equation it must be at a lower pressure.
Therefore, there is a difference in pressure between the outside and the inside, which creates an outward net force on the window, so will it open outward and not inward as intuition states. Is this right?
 

Answers and Replies

  • #2
denverdoc
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Why would the pressure be less on the outside of the window? There are two components to the external pressure in this case, the static atmospheric pressure and the dynamic pressure caused by the wind. The static is opposed from the inside, but not the dynamic. Do you have an eqn for dynamic pressure?
John
 
  • #3
Applying Bernoulli to points A (outside) and B(inside):

P_A + 1/2ρv^2=P_B

But P_B=P_atm. So:

P_A=P_atm - 1/2ρv^2, ρ is the density of air.

So the windows should pop out. Right?
 
  • #4
denverdoc
963
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I don't think this is a proper use of Bernoulli's since the two systems are not in contact.

The force of the outside is represented correctly however as is the sum of the dynamic and static pressures, as is the inside. so Pa-Pb=1/2Pv^2, ie from substitution and the following,


Pa=atm plus 1/2Pv^2
pb=atm
 
  • #5
NoTime
Science Advisor
Homework Helper
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If you actually go in a tall building you can watch the large glass window panels flex both in and out.
So the direction would depend on the flex state at the point of failure.
I would think turbulence plays a major role here.

Since I've seen an example of one failing, I stay away from them when they start to get major deflections.
 
  • #6
denverdoc
963
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If you actually go in a tall building you can watch the large glass window panels flex both in and out.
So the direction would depend on the flex state at the point of failure.
I would think turbulence plays a major role here.

Since I've seen an example of one failing, I stay away from them when they start to get major deflections.

No doubt, but I don't think this is what Gyro's ? was about. I was assuming a constant wind perpendicular to the window which should bend it it, now gusting, aerodynamic flutter, the elasticity of the mount, and mother nature might well conspire to cause it to break out.
 
  • #7
So, i can't apply Bernoulli's to this situation?
 
  • #9
It happens that I found an exercise in Physics for scientists and engineers by Serway, which is exactly similar to this, and they apply Bernoulli to points outside and inside the building. I do not know what to believe :S , maybe I need to make some experiments. :)
 
  • #10
denverdoc
963
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No I think I might have misled you in some respects because I'm used to seeing it used mostly in the context of a contiuous stream. If you scroll down about 2/3'rds the page I linked, you will see the solution for stagnation pressure which applies here.
 

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