A demo is to tie two pieces of string to the neck of an empty drinks bottle. They are free to flop about. Now pull the ends in opposite directions you find you can lift the bottle. By keeping on the tension but having your hands at different heights you find you can alter the angle the bottle hangs at. Simplistic, I know, but a good first step to introducing rotor stiffness and hinge offset.
If the string was replaced with straws you would be able to push the bottle sideways. Because the neck of the bottle is above the centre of gravity the bottle will tip.
Again, simplistic, but it is the offset of the thrust from the cg that allows a rotor with no hinge offset to impart a moment. As the body rolls the force vectors come in to line and the roll or pitch stops.
Last edited by dClbydalpha; 26th Sep 2016 at 16:26.
Reason: To complete the answer.