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# Kinematic Pair

When two kinematic links are connected in such a way that their motion is eitherย completely or successfully constrained, these two links are said to form a kinematicย pair.

Kinematic pairs can be classified according to:

## Kinematic pairs according to nature of contact:

### a. Lower Pair:

A pair of links having surfaced or area contact between the members isย known as a lower pair. The contact surfaces of two links are similar.

Examples: Nut turning on a screw, shaft rotating in a bearing.

### b. Higher Pair:

When a pair has a point or line contact between the links, it is known as aย higher pair. The contact surfaces of two links are similar.

Example: Wheel rolling on a surface, Cam and Follower pair etc.

## Kinematic pairs according to nature of contact:

### a. Closed Pair:

When the elements of a pair are held together mechanically, it is known asย a closed pair. The two elements are geometrically identical; one is solid andย full and the other is hollow or open. The latter not only envelops the formerย but also encloses it. The contact between the two can be broken only byย destruction of at least one of the members.

### b. Unclosed Pair:

When two links of a pair are in contact either due to force of gravity orย some spring action, they constitute an unclosed pair. In this, the links areย not held together mechanically, e.g. cam and follower pair.

## Kinematic pairs according to Nature of Relative Motion:

### a. Sliding pair:

When two links have a sliding motion relative to another; the kinematic pairย is known as sliding pair.

### b. Turning pair:

When one link is revolve or turn with respect to the axis of first link, theย kinematic pair formed by two links is known as turning pair.

### c. Rolling pair:

When the links of a pair have a rolling motion relative to each other, theyย form a rolling pair.

### d. Screw pair:

If two mating links have a turning as well as sliding motion between them,ย they form a screw pair.

### e. Spherical pair:

When one link in the form of sphere turns inside a fixed link, it is aย spherical pair.