Q.What is rolling friction? How does it arise?

Step 1. Rolling motion is defined as motion in which the point of contact between the moving body and the surface keeps changing continuously, rather than staying fixed as in sliding.

Step 2. The friction that arises between two bodies in this rolling-contact situation is called rolling friction.

Step 3. For the same pair of surfaces, the ordering is always static friction $>$ kinetic friction $>$ rolling friction — rolling friction is the smallest of the three, since a rolling contact avoids the large-scale sliding of one surface's molecules directly across the other's.

Step 4. This is exactly why ball bearings — which let one part roll against another rather than slide — are deliberately introduced into machinery to reduce friction losses and raise mechanical efficiency.

State the definition of rolling motion/friction and its comparative magnitude versus static and kinetic friction.

Assuming rolling friction is zero rather than merely the smallest of the three types — a rolling body still experiences some frictional resistance.