Lets do some physics! For large Reynolds number (https://en.wikipedia.org/wiki/Reynolds_number) the drag coefficient for a sphere is about Cd=0.5. The typical mass and diameter of a ping-pong ball is about 2.7g and 40mm, respectively, and thus with a density of 0.081g/cm^3 The drag force is Fd = 0.5 rhoair C_d A v^2 and the weight is Fg=4 pi/3 R^3 g rhoball For a given angle of deflection alpha one gets Fd=Fg tan(alpha) and thus v=8.5524 sqrt(tan(alpha)) So by measuring the angle of deflection of the ball we can measure the wind velocity.