Ok so I have a ball tied to a string hanging. I start a fan and the string now forms an angle. I have heard that there is a relationship between the force on the ball and the wind velocity (obviously) It should be something like F=kv^2 or something like that, what I need to find out is the magnitude of this constant. I have a series of angles (enabling me to calculate the drag of the ball). Using this I would like to calculate the velocity of the wind colliding with the ball, any ideas?