Algodoo

So, the reason this works, is because of a phenomenon known as "Centrifugal Force".

Basically, as objects rotate around, the outer objects just want to go straight parallel to the center of rotation.
The reason it doesn't just fly apart is because of forces pulling it in an equal amount to this centrifugal force.

A good example is the Earth's orbit around Sol. Without gravity, it would just fly away, due to centrifugal force.