# Wind Pressure/Force on roof

1. Jun 12, 2007

### ku1005

1. The problem statement, all variables and given/known data

"Wind (density=1.29kgm^-3) blows over a flat roofed building of height 20m at 12ms^-1.The area of he roof is 100m^2.What is the magnitude and direction of the force exerted on the roof if the pressure difference between inside and outside is due solely to the fact that the inside air is still?Assume laminar flow."

2. Relevant equations

Im really stumped with this Q, I have scanned the net and it seems to involve the Bernoulli Eqn , however, i dont really understand whats occuring, any help appreciated.

3. The attempt at a solution

2. Jun 12, 2007

### siddharth

If you assume that the thickness of the roof is negligible, what's the pressure of the air just outside the roof, where the air is flowing? And the pressure inside where the air is stationary? So, what's the force due to the pressure difference?

3. Jun 13, 2007

### ku1005

thats the thing, i undererstand where the pressure difference comes from, but not how to calculate it based on the dimensions of the roof???...

4. Jun 13, 2007

### siddharth

The dimensions of the roof is needed to calculate the force due to the pressure difference. You need to use Bernoulli's equation to calculate the pressure difference. (Hint: The air inside is stationary, while outside, it's moving.)