Description:

We have actually constructed two versions of this exhibit:

• The first version had two dots marking the two foci. A ball shot (or launched from a ramp) from one focus would bounce off any edge point and hit the ball placed at the other focus.
• The second elliptical pool table, shown above, has a single pocket located at one focus. A ball shot from the other focus to any point on the edge of the table will reflect into the pocket.

Balls which cross the line joining the foci will continue to reflect between the foci. Balls which cross the major axis beyond the foci will never cross between the foci.

Purpose:

This popular exhibit sparks interest in the special properties of ellipses.

Applications, Connections & Extensions:

See the Connections Project exhibit ellipti-light which uses a light beam and a mirrored elliptical frame to illustrate the reflective properties of ellipses. Students often use the ellipti-light table to explain the path followed by the ball on the ellipti-billiards table.

References:

The Ellipti-billiards and ellipti-light tables were designed and constructed by Alan Brix, a New Trier High School physics teacher.

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