Parabolic Billiard

Accord­ing to the opti­cal prop­erty of parabo­las, a ray falling par­al­lel to parabola’s axis gets to its focus after reflect­ing from its sur­face. A par­a­bolic bil­liard model demon­strates the opti­cal prop­erty using mechan­ics.

One of the bil­liard’s sides has a form of parabola. The pocket is in its focus. A slide fixed on the guide rail can be moved, but at any posi­tion it remains par­al­lel to parabola’s axis. A ball rolling down the slide always makes it to the pocket!

When man­u­fac­tur­ing, it is worth pick­ing the parabola’s para­me­ters so that the pocket (parabola’s focus) was nor too close nei­ther too far from the ver­tex. The slide should rest against the straight side of the bil­liard to stay par­al­lel to its axis when shifted.

The ball, the slide height and the bil­liard’s sur­face mate­r­ial should be cho­sen so that after reflect­ing from the wall the ball would not reach the pocket too fast – fly­ing over the pocket rather than falling in it.