# Force exerted by moving air?

1. May 5, 2005

### infamous_Q

is there a way to calculate this?

2. May 5, 2005

### quasar987

"Air coming at you" or "you coming at air", that's the same thing. Only the relative speed of you to the air is what matters in determining the force.

Usually, it is reasonable to assume the force of friction with the air is of the form f = -bv, where b is a constant depending on the shape of the body which must be determined experimentally.

Now quoting Symon, pp.36:

"However, for small heavy bodies [...], a better approximation may be f = bv²."

3. May 5, 2005

### kevinalm

Obviously yes, but from the way your question is worded you are looking for a simple formula. There is none. The force air exerts on an object is extremely dependant on the way air flows around it. That means the shape of the object is very important. If you're really interested, find some good texts on aerodynamics (and/or hydrodynamics). Be warned, some serious math is involved.

4. May 5, 2005

### DaveC426913

Well, in ideal terms, the air resistance is proportional to the cross-sectional area of the object and the square of the speed.

5. May 6, 2005

### FredGarvin

If you want to generalize and treat the object as a flat plate in a fluid stream you can calculate the dynamic head, as in $$P_D = \frac{1}{2}\rho V^2$$. Assuming your units are correct, that will give you a pressure which can be used to calculate the force over the entire area.

6. May 6, 2005

### infamous_Q

k thanks everyone..guess im gonna have to do some research huh.

ah and just a quick question..to go from pressure to force i'd just divide the pressure by how big the surface is correct? (since pressure is usually force exterted / area)