All the shapes we'll be talking about in this chapter are slices out of a cone.

If you slice a cone horizontally, you get a circle:

What makes a circle a circle?

Geometrically, that is... Yes, I know circles are round, but, let's get a little more specific.

A little more technically, all those red points on the circle are the same distance from the green center point.

What if you took a long rope and a board or plank... Can you think of a way to make a crop circle?

Check out this link: CircleMakers.org

Yeah, circles are cool things -- you see them everywhere. But, spheres are really where it's at!

Slices of spheres are used for all sorts of lenses in optics.

This Fresnel lamp uses slices of spheres to help aim light.

Here are some links where you can see spheres in action:

Molecular Expressions: Science, Optics and You