A part of a machine or a member of a mechanism, connecting other parts or members and having a relative motion with one another.

• It can be a binary (2 joints), ternary (3 joints) or Quaternary (4 joints)

## Mechanism

It can be defined as when the assembly of different bodies is done in such a way that the motion of one causes constrained or predictable motion to other members.

In other words, when one of the links of a kinematic chain, a combination of kinematic pairs (combination of two links), is made fix the chain can be called as a mechanism.

• A mechanism may be used for transmitting the motion or for modifying the motion.
• A machine itself is a mechanism or a combination of mechanisms and a machine apart from imparting motion also transmits and modifies the available mechanical energy to some other desired work.
• A mechanism can be a Simple Mechanism or a Compound Mechanism.
• When number of links forming a mechanism is four, is a case of Simple Mechanism whereas a mechanism consisting more than four links is regarded as Compound mechanism.
• Four bar mechanism (4 links & 4 turning pairs), slider crank mechanism (4 links, 3 turning pairs and 1 sliding pair) and double slider crank mechanism (4 links, 2 turning & 2 sliding pairs) are the three types of simple mechanisms.

## Kinematic Pair

• Two links or elements when in contact have constrained motion (successfully or completely).

### Types of Kinematic Pair

#### Based on Nature of Contact

• Lower Pair- having surface or area contact. e.g., shaft motion in bearings
• Higher Pair- point or line contact types. e.g., cam and follower pair

#### Based on Nature of Relative Motion

• Sliding Pair- relative motion is sliding.
• Turning Pair- having turning or revolving motion.
• Rolling Pair- having rolling motion relative to each other.