How to make a game with a static scene and balls that can bounce on it? What is used for this, generally? Physics engines? Even if this is a simplistic example?
The simplest way would be good if the static scene only has straight walls and flat ground. All you would have to do is multiply one of its components speeds by -1. If it collides with a wall, this would be the x component. If it is the ceiling or floor, this would be the y component. If you want to add in friction, multiply instead by -.7 or something similar.