# Kinematic Pair: Definition, Classification with Example [PDF]

Contents

## What is Kinematic Pair?

Kinematic pair is defined as two links or elements of a machine in contact with each other. If the relative motion between them is completely constrained in a definite direction, the pair is known as the Kinematic pair.

## Types of Kinematic Pairs

According to the following consideration, Kinematic Pair has been classified into three types

1. Based on Types of relative motion
2. Based on Type of Contact
3. Based on Type of mechanical constraint

### Based on types relative motion

They are furthur categorized into 5 parts :

1. Sliding,
2. Turning,
3. Rolling,
4. Screw and
5. Spherical Pair.

#### Sliding Pair

Sliding pair consists of two elements connected such that one is constrained to have a sliding motion relative to another.

Example:

• Rectangular bar in a rectangular hole
• Square bar in the square hole
• Piston and cylinder of an Ic engine.
• Tail-stock and lathe bed, etc.

#### Turning Pair

A turning pair consists of two elements connected in such a manner that one is constrained to turn or revolve about a fixed axis of another element.

Example:

• Shaft with a collar at both ends revolving in a circular hole.
• The crankshaft of an Internal Combustion engine turning in a bearing.
• Cycle wheel revolving about its axles.

#### Rolling Pair

A rolling pair consists of two elements connected in such a manner that one is constrained to roll in another fixed element.

Example:

• Ball and roller bearings.
• Wheel rolling on a flat surface.
• Marble rolling on a flat surface.

#### Screw Pair

A screw pair consists of two elements connected in such a manner that one element turns about the other element using threads. The motion, in this case, is a combination of sliding and turning.

Example:

• The lead screw of a lathe and nut.
• Nut and bolt combination
• Screw with nut of screw jack.

#### Spherical Pair

This consists of two elements connected in such a manner that one element that is in the form of a sphere turns about the other fixed element.

Example:

• Ball and socket joint.
• Pen stand
• Minor attachment of vehicles.

### Based on type of contact

Types of contact classified as

1. Lower pair
2. Higher Pair

#### Lower pair

When the two elements have surface contact when relative motion takes place and the surface of one element slides over the surface of another element, the pair forms a lower pair.

Example:

• All sliding, Turning and Screw pairs are lower pair.
• Nut turning in a screw.
• shaft rotating in a bearing.
• Universal joint
• All pairs of slider-crank mechanism.

#### Higher Pair

When the two elements of a pair have line contact or point contact when relative motion takes place and the motion between the two elements is partly turning & sliding then the pair is known as higher pair.

Example:

### Based on type of Mechanical constraint

Types of Mechanical Constraint classified into two types,

1. Self closed pair and
2. Force closed pair.

These are further classified into the following types :

#### Self closed pair or closed pair

whenever two elements of pair are held together mechanically in such a way that only the required type of relative motion occurs is called as Self closed pair or closed pair.

Example: All lower pairs.

#### Force closed pair or Unclosed pair

whenever two elements of pair are not held together mechanically but are kept in contact by the action of external forces, the pair is said to be Force closed pair or Un-closed pair.

Example: Cam and spring-loaded follower pair.

## FAQ’s

### What is Kinematic Pair?

If the relative motion between two links is completely constrained in a definite direction, the pair is known as the Kinematic pair.

### What are higher and lower kinematic pairs?

When the two elements of a pair have line contact or point contact when relative motion takes place and the motion between the two elements is partly turning & sliding then the pair is known as higher pair.

When the two elements have surface contact when relative motion takes place and the surface of one element slides over the surface of another element, the pair forms a lower pair.

## Conclusion

To conclude we can say that kinematic pairs are essential in the field of mechanical engineering which helps to understand the motion and working of a machine. By understanding different kinematic pairs, engineers can design the machine to perform desired motion.