Applied Mechanics and Graphic Statics
The characteristic of a couple is:

All listed here
Algebraic sum of moments of forces, constituting a couple, about any point, is same
Algebraic sum of forces, constituting a couple is zero
A couple can be never the balanced by a single force

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Applied Mechanics and Graphic Statics
Kinetic friction may be defined as

Friction force acting when the body is just about to move
Angle between normal reaction and resultant of normal reaction and limiting friction
Friction force acting when the body is in motion
Ratio of limiting friction and normal reaction

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