When the elements of a pair are kept in contact by the action of external forces, the pair is said to be a

A. μ₁ = μsinβ B. μ₁ = μcosβ C. $${\mu _1} = \frac{\mu }{{\sin \beta }}$$ D. $${\mu _1} = \frac{\mu }{{\cos \beta }}$$

A. Self-closed B. Force-closed C. Friction closed D. None of these

A. Sliding B. Turning C. Rolling D. Screw

A. None of the links is fixed B. One of the links is fixed C. Two of the links are fixed D. None of these