posted by Katie on .
If wind blows at a speed of 30 m/s over the roof of your house, what is the pressure diference on your roof between the air inside and the air outside? What net force does this produce on a roof having an area of 175 m^2?
1.3 kg/m^3 is the density of air.
(1/2)*(air density)*V^2*(roof area), but depends upon what the pressure inside the house is, and that depends upon which windows or doors are open.
Wind pressure (suction) over a roof is the same phenomenon as the force that lifts an airplane by air flowing past the wings.
When there is an obstruction to the wind, the air flow speeds up to compensate for the reduced sectional area, and in doing so, creates a negative pressure on the leeward side of the building.
Most of the time, the magnitude of the negative pressure is compared with the stagnation pressure ((1/2)ρv²) and thus creates a factor which is dependent on the shape of the building, shape of the roof, and the location. See ref. below.
Different building codes in different states/countries adopt values for these factors. For the purpose of this question, your teacher has probably given you a shape factor for the house in question.
The net force is the product of the negative pressure and the area of the roof.
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