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

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

ANSWER DOWNLOAD EXAMIANS APP

Applied Mechanics and Graphic Statics
The angle of friction is:

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

ANSWER DOWNLOAD EXAMIANS APP