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

This is the equation for friction:

>f = u N
>
>f = The force of friction
>
>u = The coefficent of friction
>
>N = the Normal force (for this conversation: how heavy it is)

You’re right, round metal wheels on flat metal bars has a pretty low coefficent of friction. However trains are fucking giant and heavy. That means they both have a high Normal force, and also don’t need that much friction since they accelerate/decelerate slowly due to high inertia.