circle.velocity.x -= 2 * dot * bounceLineNormal.x; circle.velocity.y -= 2 * dot * bounceLineNormal.y; The collisions currently reverse the velocity of the circ

circle.velocity.x -= 2 * dot * bounceLineNormal.x; circle.velocity.y -= 2 * dot * bounceLineNormal.y; The collisions currently reverse the velocity of the circle relative to the line by subtracting to cancel and then subtracting again to negate. I found a slightly nicer-looking effect can be gained by making the factor ~1.8 to simulate 20% energy loss in collisions. Obviously, any magic numbers in the code are not relevant for its purpose of demonstrating a simple mathematical concept in a literary style. I'd love to see more examples of this kind around HN as it's a quick way to learn/refresh the odd concept.