Question

Why do trains use steel wheels rather than rubber tires?                                                                  A) 

Steel wheels provide more grip, making it easier to stop a train. B) 

Rubber tires don't provide enough friction to allow the train to move.
C)  Steel wheels increase friction, thus making it easier to move the load.
D)  Steel wheels reduce friction, thus requiring less force to move the load.

Answer 1

Steel wheels reduce friction, thus requiring less force to move the load.

Answer 2

D) steel wheels reduce friction, thus requiring less force to move the load. Friction between rubber and steel would be greater than steel and steel. Friction creates heat, which represents a loss of energy (which has to come from somewhere else - likely from the kinetic energy of the train)