How can trains move on rails? if the wheels are smooth and the rails are also smooth, how can it be enough friction for it to move?

Question

How can trains move on rails? if the wheels are smooth and the rails are also smooth, how can it be enough friction for it to move?

In: 2785

Answer 1

Because the force of friction is equal to the coefficient of friction multiplied by sin of the angle perpendicular to the surface, times the weight of the object, and trains are HEAVY. A single car weighing 120 tons is not uncommon.