Applied Mechanics and Graphic Statics
The following is in unstable equilibrium

A uniform solid cone resting on its base on a horizontal plane
A solid cube resting on one edge
A satellite encircling the earth
A uniform solid cone resting on a generator on a smooth horizontal plane

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Applied Mechanics and Graphic Statics
The angle of friction is:

The force of friction at which the body is just about to move
The angle between the normal reaction and the resultant of normal reaction and limiting friction
The force of friction when the body is in motion
The ratio of the friction and the normal reaction

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