Centripetal Force

Why is it when you spin something, it stays on the plane that you spin it on? Does gravity not affect it? I would think that it would... in b4 gb2/4th grade science/

A bucket of water on a rope and a spinning top or gyroscope work on different principles.
Bucket of water stays up/full because of inertial effects (centripetal 'force' isn't really a force, it's just easier to pretend it exists for mathematical purposes).
Spinning top stays upright thanks to gyroscoping precession - any force attempting to shift the orientation of the axis of rotation will produce another force that is perpendicular to both the axis of rotation and the external force.