Mechanics (friction): Identify the change that reduces friction most effectively in machine parts. Consider contact type and deformation at the interface. Choose the correct change.

Given data

• Topic: Reducing friction.
• Choices compare rolling vs. sliding and lubrication vs. dry contact.

Concept/Approach
Rolling friction is typically much lower than sliding friction because there is less interfacial shearing and often smaller real area of contact.

Reasoning
• Replacing plain surfaces with rollers/ball bearings converts sliding to rolling. • Options that move toward sliding or remove lubrication increase friction.

Common pitfalls
Assuming rolling friction can be higher—true only in rare edge cases (e.g., severe deformation).

Final Answer
From sliding friction to rolling friction