Assertion(A) : Machines such as steam engine, the automobile engine, etc., that produce rotational motion have a disc called a flywheel. It prevents jerky motions, thereby ensuring a smooth ride.  
Reason(R) : Because of large moment of inertia, the flywheel resists the sudden increase or decrease of the speed of the vehicle. It allows a gradual change in the speed.

Assertion (A) is correct. Machines like steam engines and automobile engines that produce rotational motion often have a disc called a flywheel. The purpose of the flywheel is to prevent jerky motions and ensure a smooth ride.

Reason (R) is also correct. The flywheel, due to its large moment of inertia, resists sudden changes in speed. It stores rotational energy and allows for a gradual change in speed, contributing to the overall stability and smooth operation of the machine.

A and R are true and R is the correct explanation of A