Gyroscopic Precession:

This is the tendency of the spin axis of a rotating body to twist at right angles to any applied tipping force. This effects all spinning bodies including the planet Earth, which wobbles on its axis like a top, giving rise to the "precession of the equinoxes". You can feel this force by gripping the axel of a spinning wheel and trying to tilt it. The strange twisting motion that results is due to gyroscopic precession. It’s this effect which makes a moving two wheel bike turn in the direction that the rider leans.