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?
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The resulting movement between the wheel and the track is a function of both the force applied by the train on the track (ie. The weight of the train) and the coefficient of friction between the 2 surfaces. It is also a function of the size of the contact area between the 2 surfaces, however this doesn’t matter much in this discussion as I will clarify below.
As you mentioned, both surfaces are smooth metal surfaces, so the coefficient of friction is very low. That being said, the weight of the train is so massive, that even with this low coefficient of friction movement is achieved. Now that friction is achieved, we just need to ensure that the engine provides enough power to move the train in the horizontal direction.
The contact area between the wheel and the track can theoretically* also be increased if the weight of the train cant possibly increase enough (*this never applies in real life since the track is of constant size). This is however what many race cars must do, as they are looking to minimize weight.
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