Kinematic pair
When two links of a machine are joined in such a way that the motion between them is in a definite direction, it is said to form a Kinematic pair. The Kinematic pairs are of following types.
According to the type of motion:
a). Turning pair: One link slides over another link. Example – Cycles wheel turn about the axle.
b). Sliding pair: One link turns or revolves about fixed axis of another link. Example – Piston and cylinder
c). Rolling pair: One link rolls over another fixed link. Example – Ball bearings
d). Spherical pair: One link of spherical shape turns or swivels about another fixed link. Example – car mirror.
e). Screw pair: One link can turn about the other by screw threads. Example – nut and bolt.
According to type of contact:
a). Lower pair: Two links or elements having surface contact between them. Example – ball bearings, cam and follower etc.
b). Higher pair: Two links or elements having line or point contact between them. Example – sliding and turning pairs.