The "first" video game: Pong. Deceptively simple. Two paddles, and a ball in the middle that bounced back and forth. It is not simple for two reasons: First, whenever the ball strikes the paddle, its y component of speed remains the same but in an opposite direction, and the only way that the x component can change direction is when the ball hits the wall. This means that the world of pong is perfect, where both the paddles and ball are frictionless, and there is no air resistance. Also, when the ball strikes the paddle, it is reflected back at some angle. This reflection of the ball is similar to the reflection of light rays that strike a mirror.