A sphere has two sides. However, there are one-sided surfaces.

[Tombstone]

Möbius Strip

A sphere has two sides. A bug can be trapped inside a spherical shape or crawl on its visible surface.

A sheet of paper also has two sides.

The first one-sided surface was discovered by A. F. Möbius (1790-1868) and bears his name: Möbius strip. Sometimes it's alternatively called a Möbius band. (Actually, the surface was described independently and earlier by a couple of months by another German mathematician J. B. Listing.)

The strip was immortalized by M. C. Escher (1898-1972).

[Bill Sikes]

Originally Posted by Tombstone

Möbius Strip
The first one-sided surface was discovered by A. F. Möbius (1790-1868) and bears his name: Möbius strip. Sometimes it's alternatively called a Möbius band. (Actually, the surface was described independently and earlier by a couple of months by another German mathematician J. B. Listing.)

The strip was immortalized by M. C. Escher (1898-1972).

This is a very useful thing - can you think of where it is used today?

[Warsai]

Originally Posted by Bill Sikes

This is a very useful thing - can you think of where it is used today?

Roller coasters? Just kidding.

My neighbor puts mobius strips to good use, she takes one half-twist and puts it around her neck, and then takes the other half-twist and puts it around her ponytail.

[Bill Sikes]

(uses for a moebius strip)

Originally Posted by Warsai

Roller coasters? Just kidding.

Could be fun..... you're sort of thinking along the right lines, too, but go
a bit more industrial....