Short Answer:

Higher pairs are kinematic pairs in which the two elements have point or line contact with each other during relative motion. In these pairs, the contact area is very small compared to lower pairs, which results in higher pressure and wear at the contact points.

Examples of higher pairs include gear teeth, cam and follower, ball and roller bearings, and wheel on a rail. These pairs are used where precise and controlled motion is required, even though they involve more friction and wear than lower pairs.

Detailed Explanation :

Higher Pairs

In the study of kinematics of machines, pairs are classified based on the type of contact between the two elements. A higher pair is formed when two mechanical elements are in point contact or line contact with each other during relative motion. Unlike lower pairs where surface contact exists, higher pairs have a smaller contact area, leading to more wear and less stability, but allowing more complex and precise motion.

Higher pairs are common in mechanisms where smooth rolling or cam-type motion is needed. They are used in applications that involve intermittent, precise, or rotational motion such as in gears, cams, and bearings.

Characteristics of Higher Pairs

1. Type of Contact:
   The elements have point or line contact instead of surface contact. For example, gear teeth contact along a line, while a cam and follower contact at a point.
2. Nature of Motion:
   Higher pairs produce sliding or rolling motion depending on their design. For instance, in ball bearings, rolling motion occurs; in cam-follower systems, both rolling and sliding exist.
3. Wear and Tear:
   Since the contact area is smaller, the pressure on the contact surface is higher, leading to increased wear and the need for proper lubrication.
4. Precision in Motion:
   They are preferred in systems requiring accurate motion transmission, such as in gear trains or cam mechanisms, where timing and movement are critical.
5. Less Stability:
   Compared to lower pairs, higher pairs have less stability because the contact area is limited. Hence, they are used only where point or line contact is functionally necessary.

Types and Examples of Higher Pairs

Higher pairs can be broadly divided into two main categories based on the type of contact between the elements:

1. Point Contact Higher Pairs:
   In this type, the two elements touch each other at a single point during motion. As motion occurs, this point of contact changes its position continuously.
   • Example: A cam and follower mechanism, where the cam profile touches the follower at a single point and transfers motion. Another example is a ball bearing, where the balls have point contact with the inner and outer races.
2. Line Contact Higher Pairs:
   In this type, the two elements are in contact along a line during their relative motion. This line contact shifts as motion continues.
   • Example: The gear teeth in mesh form a line contact. Similarly, the wheel and rail system in railway locomotives or trolleys also forms a line contact.

Examples of Higher Pairs in Machines

1. Cam and Follower Mechanism:
   In this mechanism, the cam rotates and pushes the follower upward through direct contact. The cam surface and follower meet at a point which changes during motion, forming a higher pair.
2. Gear Teeth Contact:
   When two gears mesh together, the teeth of one gear contact the other along a line. This contact line continuously changes during rotation, creating a line contact higher pair.
3. Ball and Roller Bearings:
   The rolling elements (balls or rollers) in a bearing contact the inner and outer races either at a point or along a line. They reduce friction and allow smooth rotation under load.
4. Wheel and Rail System:
   The wheel of a train or trolley moves on the rail, forming a line contact higher pair. This design allows rolling motion and supports heavy loads with less frictional resistance.
5. Belt and Pulley System:
   The belt and pulley contact each other along a line or narrow area, transferring motion through frictional contact. This also represents a type of higher pair.

Comparison between Higher and Lower Pairs

Aspect	Higher Pair	Lower Pair
Type of Contact	Point or line contact	Surface contact
Area of Contact	Small	Large
Nature of Motion	Rolling or sliding	Sliding, turning, or screw motion
Friction and Wear	High due to small contact area	Low due to larger contact area
Stability	Less stable	More stable
Examples	Cam and follower, gears, ball bearings	Piston and cylinder, hinge joint

(Note: The explanation is descriptive only; no table or graph presentation is used.)

Importance of Higher Pairs in Machines

Higher pairs play a significant role in mechanical systems that require precision, controlled timing, and smooth rolling contact. Some key points include:

1. Accurate Motion Transmission:
   Higher pairs ensure proper timing and movement between machine elements such as gears or cams.
2. Compact Design:
   They allow compact mechanism designs while performing complex motion conversion, such as converting rotary motion into linear or oscillating motion.
3. Reduced Sliding Friction (in rolling pairs):
   Rolling elements like ball and roller bearings reduce friction compared to pure sliding motion.
4. High-Speed Applications:
   Many higher pairs can operate efficiently at high speeds when properly lubricated.
5. Essential in Precision Mechanisms:
   Used in instruments, automation systems, and automotive components where exact motion reproduction is needed.

Advantages of Higher Pairs

• Enable precise and controlled motion.
• Compact and efficient for transmitting motion over small spaces.
• Allow smooth rolling contact, reducing energy loss.

Disadvantages of Higher Pairs

• High wear and friction due to small contact area.
• Require good lubrication and maintenance.
• Less stable under heavy load compared to lower pairs.

Conclusion:

Higher pairs are important elements in mechanical systems that require precise and controlled motion, though they involve point or line contact leading to more wear and less stability. Despite their disadvantages, they are indispensable in mechanisms such as gears, cams, bearings, and wheels, where accurate motion transfer is essential. Thus, higher pairs form the backbone of many high-performance and precision-based machines used in modern engineering applications.