I drew a bunch of random lines. Your welcome. Just kidding, let me explain what these mean: Grey - Vector from start point of platform to ball. Green - Projection of grey vector onto tangent vector. Shaded Point - Edge of the projection (point used in collide block). Blue - Vector from shaded point to ball (aka normal vector). Red - Ball Velocity Purple - Projection of red vector onto blue (normal) vector. These vectors/points are included in my Ball Physics Tutorial. Some things to notice, by the way: - The blue normal vector is always pointing outwards, usually at a 90 degree angle. - The purple vector (projected velocity) is reversed when colliding, but the red vector isn't quite reversed.