Higher Pair in Mechanical Engineering

In mechanical engineering, a pair refers to the connection between two elements that allows relative motion between them. A higher pair is a type of pair that involves both sliding and turning motions between the elements. Let's analyze each option to determine which one qualifies as a higher pair.

A) Belt and Pulley
A belt and pulley system involves the use of a flexible belt wrapped around a pulley. As the pulley rotates, the belt moves along its surface, resulting in a combination of sliding and turning motion. Therefore, a belt and pulley system can be considered a higher pair.

B) Turning Pair
A turning pair, also known as a revolute pair, consists of two elements that are connected by a pin joint or a hinge. This type of pair allows only a pure turning motion between the elements and does not involve any sliding motion. Therefore, a turning pair is not considered a higher pair.

C) Screw Pair
A screw pair involves the connection between a screw and a nut. The screw has a helical thread on its surface, which engages with the corresponding thread on the nut. When the screw is rotated, it moves axially in relation to the nut, resulting in both turning and sliding motion. Therefore, a screw pair can be considered a higher pair.

D) Sliding Pair
A sliding pair, also known as a prismatic pair, allows only pure sliding motion between the connected elements. This type of pair does not involve any turning motion. Therefore, a sliding pair is not considered a higher pair.

Conclusion
Among the given options, both the belt and pulley and the screw pair involve a combination of sliding and turning motions. However, the belt and pulley system is more commonly associated with a higher pair in mechanical engineering. This is because it allows a larger range of motion and can transmit power more efficiently compared to a screw pair. Therefore, the correct answer is option 'A' - Belt and pulley.