Gyroscope
A spinning wheel has some very strange forces acting on it. Click to see a 100kb movie.

Can you hold a bicycle wheel upright with one finger?

You can, as long as the wheel is spinning.

After viewing the movie on the left can you explain why it is hard to fall off a bicycle if it is moving at high speeds.

A spinning wheel produces strange forces. Tilting a spinning wheel is difficult. A spinning wheel exerts forces that oppose any external forces that act to tilt it.
The forces generated by the spinning wheel as it is tilted spin the person around on a rotating chair.