Ellipse

A red and yellow table with a large blue ellipse in the centre.

An ellipse has two focal points.

How it works

Release a ball so it rolls down a ramp, across a black dot and around an elliptically-shaped billiard table. The ball will roll into a hole at the other end of the table if it rolls over the ellipse’s focal point (the black dot).

Things to try or ask around the exhibit

  • Why is it important to roll the ball across the black dot?
  • Where does the ball finish up?

Background

The table is a ellipse-shaped and the black dot is located at one of the ellipse's focal points. When the black dot is at one focus and the hole is at the other, the shape of the table ensures that the ball lands in the hole.

The orbits of planets around our Sun are ellipses, with the Sun at one focus. You will also find ellipses in the gears and cams of machines.