So there it is me trying to program some simple physics for flying ball. I have done some research and generally I was always understanding physics very well. But what is happening in my application is not understandable for me, even tho I have checked everything twice and I think everything should have worked good. So my physics is very simple, only gravity and air resistance, no spinning of ball etc. My ball has few attributes, which are: -position(in meters, I also assume that one 1px==1m), -mass(in kg), -radius(in meters), -speed, which is basically a vector with direction and value (in m/s). In physics engine I assume g=9.81 [m/s^2] and air density of q=1.2041 [kg/m^3]. Now thats how I calculate where to move the ball: (1)I move the ball according to its actual speed vector. (2)I calculate forces on the ball: gravity: Q= g*m [thats a vector always directed downwards] air resistance: F= (0.47*q*A*v^2)/2 where: F is air resistance [N] 0.47 is drag coefficient for the ball (found on wiki) q is density of air A is the cross-sectional area of the ball v is speed of the ball the air resistance is always directed opposite to actual speed total force (Ft) on the ball by adding both vectors for Q and F (3)Now I can calculate acceleration of the ball by simply deviding Ft by mass of the ball (a=Ft/m) and I keep a as a vector(just like speed) with value calculated and appropriate direction calculated (I have checked it and the direction of a is calculated correctly). (4)I update the speed of the ball V1=V+a*t (time was 1 sec, but i still multiply it by time in case I want to change time intervals). I do that by simply adding 2 vectors (V and a) together. My problem is: I tested it on a ball with: -some start position with doesnt matter here -mass of 0.2 [kg], -radius of 0.01 [m], -start speed of 200 [m/s] 45% upwards Now the ball fly and it looks good. But when I change just the mass to lets say 0.6kg the ball actually fly further, like much further... Despite the fact that air density and gravity seems to be bigger. Am I calculating something wrong? Or is that how it supposed to be? Thanks for your help.