Ball-Simulator

              The Reflection algorithm on the example of Balls.

1. Coordinate system: Axis OX directed from left to right, axis OY directed from buttom to top. Y ^ . . . . .-------------->X
2. The Ball has start coordinate of centre (x,y), start direction angle in degrees (f), X-axis radius (R1), Y-axis radius (R2) and speed in pi/10ms(speed).
3. Speed splits into speed along the X-axis (newX) and along Y-axis (newY). So newX^2 + newY^2 = speed^2
4. Surface angle counts down counterclockwise /-f--- -- a
   ---/---- f - is possitive -------- a - is negative
5. The Reflection algorithm is in ballWindow.py (changeDirection(a,ball)), where a -angle of reflection and ball - reflecting ball. Algorithm based on projection on sufface of reflection, changing of vertical speed and return back to main X-Y basis.