Kinematic pair

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.

 

Questions & Answers

  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
    Answer : Sliding Pair
  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 
    Answer : Turning Pair
  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
    Answer : Screw Pair
  4. A ball and socket joint forms which pair
    Answer : Spherical pair
  5. The lead screw of a lathe with nut forms a
    Answer : Screw Pair
  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
    Answer : Lower Pair
  7. The pair is known as a higher pair when the relative motion between the elements of a pair is
    Answer : Partly turning and partly sliding
  8. When the connection between the two elements is such that only required kind of relative motion occurs, it is known as
    Answer : Self closed pair
  9. when the elements of a pair are kept in contact by the action of external forces, the pair is said to be a
    Answer : force closed pair
  10. The cam and follower is an example of which pair
    Answer :  Higher Pair
  11. An automobile steering gear is an example of which pair
    Answer : Higher Pair
  12. The two elements of a pair are said to form a higher pair, when they have
    Answer : line or point contact when in motion

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