During relative motion of two elements, if they maintain surface contact and one element's surface slides over the other's surface, which kinematic pair (as per classical mechanism theory) is formed?

Introduction / Context

Kinematic pairs are identified by the nature of contact and constraint. Understanding whether two elements share surface, line, or point contact helps predict pressure distribution, lubrication regimes, and wear.

Given Data / Assumptions

• Two rigid elements with relative sliding motion.
• Continuous surface contact (not merely line/point).
• Planar mechanism idealization.

Concept / Approach

Lower pairs have surface contact and include sliding (prismatic) pairs and turning (revolute) pairs. By contrast, higher pairs have line/point contact, as in cam–follower and gear teeth engagement. The phrase ‘‘surface slides over the surface’’ directly indicates a sliding lower pair.

Step-by-Step Solution

Verification / Alternative check

Classifications in textbooks list slider–guide and pin–hole as lower pairs; cams/gears are higher pairs.

Why Other Options Are Wrong

• Higher pair: implies line/point contact; contradicts the given surface sliding.
• Self-closed pair: describes how a pair is held together (geometric closure), not the contact nature; both lower and higher pairs can be self-closed.
• Force-closed pair: maintained by external force (e.g., spring), orthogonal to contact classification.
• Rolling pair: rolling contact (line/point), not continuous surface sliding.

Common Pitfalls

• Mixing ‘‘closure’’ terminology (self/force-closed) with ‘‘contact’’ classification (lower/higher).

Final Answer

lower pair