17) When the two elements of a pair have ______ when in motion, it is said to be a lower pair.

18) A universal joint is an example of

19) A combination of kinematic pairs, joined in such a way that the relative motion between the links is completely constrained, is called as

20) The relation between number of pairs (p) forming a kinematic chain and the number of links (l) if

21) When one of the links of a kinematic chain is fixed, the chain is known as a