Q.Briefly explain 'rolling friction'.

Friction exists as static, kinetic (sliding), and rolling friction; it can be reduced by lubrication, polishing, and using ball bearings/rollers.

Types of friction:

1. Static friction: the opposing force that acts between two surfaces in contact when there is no relative motion between them but an external force is trying to produce motion; it adjusts itself (up to a maximum limiting value) to exactly balance the applied force.
2. Kinetic (sliding) friction: the opposing force that acts between two surfaces when one is sliding over the other; it is generally somewhat less than the maximum static friction, and is roughly constant regardless of the sliding speed (for moderate speeds).
3. Rolling friction: the opposing force that acts when one surface rolls over another (e.g., a wheel or ball); it is much smaller than sliding friction for the same surfaces, because rolling avoids the continuous 'catching' of surface irregularities that sliding involves. (Fluid friction/drag, where an object moves through a liquid or gas, is sometimes listed as a fourth type.)

Methods to reduce friction:

1. Using lubricants such as oil or grease between moving surfaces, which reduces direct solid-to-solid contact. …