[ODE] more air friction

[Ivan Bolcina]

Another thing on air friction.
If I calculate the force that friction produces on a current moment with 
current speed, then this is only current air friction force.
If I then run simulation for a given dt, now this force applies for all 
dt. But air friction force should be diferent at,for example 0.5dt, 
since it has already 0.5dt time to slow down object.
So I should pass to ODE not constant force, but rather formula of air 
friction. or should I canculate avarage airfiction force, which applies 
for all dt, not just current time.


bye, ivan