Kinematic pair

Explanation

A kinematic pair is formed when two kinematic links are joined such that the joint enables a relative motion between them. Kinematic pairs are further classified as lower and upper pairs based on how the two links are in contact with each other and how they are constrained.

Types of kinematic pairs

Lower pair

When two links are joined in a way that their domain of contact is the surface or the whole area, that corresponds to one another. A universal joint and a nut on a screw are some simple examples of lower kinematic pairs. Based on the relative motion between the links, the lower pairs are further classified as shown below.

• A sliding pair is formed when two links slide about each other.
• A screw pair is formed when one of the two links follow a threaded path on the other link. This pair has both sliding and turning motion.
• A spherical pair is formed when one of the links in the form of a sphere, turns inside the other link similar to a hollow sphere.
• A turning pair is formed when one of the two links turns around the other link.

Higher pair

When a pair is connected to each other by a line of contact, or a point on the surface, or a curve on one of the links, the pair is said to be a higher pair. A ball rolling on a flat surface (rolling pair) is a good example for a higher pair.

Frequently Asked Questions

What type of pair does the belt and pulley form?

A belt and pulley system form a special case of the higher pair called as the wrapping pair. As the belt needs multiple points of contact to constrain the pulley as it rolls, they are termed as wrapping pair.