# Calculating air resistance on air

1. May 21, 2010

### E.L

Fluid Dynamics - Calculating air resistance on air

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

I'm trying to figure out how much the velocity of wind will decrease by over a given distance. I know the velocity at a point 1cm after it has passed over an object, and i need to determine the velocity at the object. The flow is turbulent and the object is oscillating.

2. Relevant equations

I know the formula for air resistance is F=1/2"rho"v^2*C*L^2, where rho is the density, v is the relative velocity, c is the coefficient of drag and L is the length.

3. The attempt at a solution

I have no idea what to do when the question concerns air resistance acting on air. I do not know how to treat length in the equation, as I don't understand how air can have a length. I also do not understand how to find the coefficient of drag on air.

Last edited: May 22, 2010
2. May 21, 2010

### diazona

I don't think that equation applies. As far as I know it's only relevant for solid objects moving through air (by the way, in the general form it's F = ρCAv^2/2, where A is cross-sectional area presented to the air).

What you're trying to calculate is like a fluid dynamics problem, and although I'm not familiar with much fluid dynamics myself, it seems fairly complex. Maybe someone else will know of a relevant equation.