Kinematic Pair: When the two Kinematic links are joined to have relative motion between them is known as Kinematic pair.

The Kinematic pairs are classified as follows.

Acc. to the nature of contact

1.      Lower pair – When the two links have surface contact between them, it is known as lower pair.

2.      Higher pair - When the two links have line or point contact between them, it is known as lower pair.

Acc. to nature of relative motion

1.      Sliding pair – When one link slides relative to another link, it is known as sliding pair.

2.      Turning pair – When one link turns or revolve relative to another link, it is known as turning pair

3.      Rolling pair – When one link rolls over the other pair, it is known as rolling pair.

4.      Screw pair – If two pairs have turning as well as rolling motion between them, it is known as screw pair.

5.      Spherical pair – When a spherical link turns inside a fixed link, it is known as spherical pair.

Acc. to nature of constraint

1.      Self closed pair – When the two links are joined together mechanically, it is known as self closed pair.

2.      Unclosed pair – When the two links are connected either due to gravity or by some external forces, it is known as unclosed pair.