# Kinematic Pair

A kinematic pair or simply a pair is a joint of two links having relative motion
between them.

## Types of kinematic pairs:

Kinematic pairs can be classified according to

(i) Nature of contact
(ii) Nature of mechanical constraint
(iii) Nature of relative motion

## Kinematic pairs according to nature of contact

(a) Lower pair: A pair of links having surface or area contact between the members is known as a lower pair. Example: – Nut and screw, shaft rotating in bearing, all pairs of slider crank mechanism, universal joint etc.

(b)Higher pair: When a pair has a point or line contact between the links, it is known as a higher pair. Example: – Wheel rolling on a surface, cam and follower pair, tooth gears, ball and roller bearings.

## Kinematic pairs according to nature of mechanical constraint

(a) Closed pair : When the elements of a pair are held together mechanically, it is known as a closed pair. The contact between the two can be broken only by destruction of at least one of the member.

(b) Unclosed pair : When two links of a pair are in contact either due to force of gravity or some spring action, they constitute an unclosed pair.

## Kinematic pairs according to nature of relative motion:

(a) Sliding pair: If two links have a sliding motion relative to each other, they form a sliding pair.

(b)Turning pair: When one link has a turning or revolving motion relative to the other, they constitute a turning or revolving pair.

(c) Rolling Pair: When the links of a pair have a rolling motion relative to each other, they form a rolling pair.

(d)Screw pair: If two mating links have a turning as well as sliding motion between them, they form a screw pair. Ex – lead screw and nut.

(e) Spherical pair: When one link in the form of a sphere turns inside a fixed link, it is a spherical pair. Ex – ball and socket joint.

1. When the nature of contact between the element of a pair is such that it can only slide relative to the other, the pair is known as
2. When the nature of contact between the elements of a pair is such that it can turn or revolve about a fixed axis, the pair is known as
3. When the nature of contact between the elements of a pair is such that one element can turn about the other by screw threads, the pair is known as a
4. A ball and socket joint forms which pair
5. The lead screw of a lathe with nut forms a
6. when the two elements of a pair have a surface contact when relative motion takes place and the surface of one element slides over the other, the pair formed is known as a