by standing on the shoulders of giants
angle(x1, y1, x2, y2) Calculate angle between two points
self.physics.velocityx and self.physics.velocityy is the velocity (speed) in pixels / second so for example if velocityx is 4 and velocityy is 3 then angle(0,0,4,3) is going to give you the angle from 0,0 to 4,3 (30 degrees ?)
Hope this helps ?