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

The simple answer is that you need a lot less force to move than you probably think. A strong person can move a train carriage by hand if it is on perfectly flat ground – all you have to is overcome the rolling resistance and let it accelerate very slowly.

In order to get something on wheels moving, you need to overcome the rolling resistance (how hard is it to make the wheels turn), the angle of the slope it’s on and any bumps it has to climb over.

Trains basically work by minimising all 3 of these factors. The tracks are very smooth so basically no bumps, the steel wheels running on greased bearings have very little rolling resistance and tracks are made as flat as possible (freight trains aim for less than 1.5% slope, or 1.5cm of height change per 1m of distance)

Once you’ve overcome the factors preventing the train from moving, it’s just mass x acceleration and trains generally don’t accelerate very quickly so they can move a lot of mass with a relatively low force

Edit: unit error…