4th Class Power Engineering Part A Practice Exam 2025 - Free Power Engineering Practice Questions and Study Guide

The type of friction that is always less than kinetic friction is rolling friction. Rolling friction occurs when an object rolls over a surface, and it typically involves less resistance compared to the sliding (kinetic) friction that occurs when two surfaces slide against each other. This lower resistance is primarily due to the nature of rolling motion, which allows for the deformation of the surfaces and the utilization of a smaller contact area, reducing energy loss.

In contrast, kinetic friction is the friction experienced by moving objects on a surface and is usually greater than rolling friction because it requires more force to overcome the sliding motion of surfaces in contact. Static friction, which prevents an object from starting to move, can be more than kinetic friction up to a certain limit, but once an object is in motion, kinetic friction takes over. Fluid friction pertains to the resistance an object experiences while moving through a fluid (gas or liquid), which can also create varying amounts of friction, often less than kinetic friction depending on the conditions.

Thus, rolling friction’s inherent characteristics and behavior in relation to other types of friction confirm that it remains less than kinetic friction in almost all practical applications.