Ellipse billiards

How does the exhibit work?

Place the ball on the dot. Try hitting the ball with the billiard. If the ball bumps against the edge, chances are it will end up in the hole.

What is the science behind it?

Never want to lose again? If so, place the ball on the dot. Now use the cue to make the ball strike the edge. There you go – it’s easy to get it in the hole. Being a champion is fun!

This snooker table has a special shape: it’s an ellipse. It looks like a stretched circle. The hole and the dot are the focal points. What happens if something in an ellipse moves from one focal point to the edge? It always bounces to the second focal point. This works for snooker balls too.

Ellipse in a whispering gallery

Imagine a large room in the shape of an ellipse. If you stand at one focal point of the ellipse, and your friend stands at the other focal point, you can hear each other perfectly. Even when you are whispering!

That’s because sound waves, like the snooker ball, are reflected from one focal point to another. It’s perfect for sharing secrets!

Do you want to try this out? You can find a whispering gallery of this sort in St. Paul’s Cathedral in London.

Ellipse of the Earth

All the planets in our solar system — including the earth — move around the sun. The paths they take have the shape of an ellipse.

A trick for drawing an ellipse

Do you want to draw an ellipse?

1. Place a flat board under a sheet of paper. Stick two drawing pins into the sheet. These will be the focal points.
2. Tie the two ends of a piece of string together and place the loop of string around the drawing pins.
3. Place a pencil inside the string, pull the string tight and move the pencil round.

You have an ellipse!

Did you notice that your string always stays the same length? This means that wherever you put your pencil on the edge of the ellipse, the sum of the distances to the foci is always the same.