It all depends whether you mean the
resistance in trainers or in trains.
Lets look at trainers first.
The resistance in a trainer
I take to mean how compressible it is when your foot touches the ground. This has to do with
Impulse. If the trainer can be compressed then this will increase the time that it takes your
foot to come to rest on impact and so the force between your foot and the ground is reduced.
Modern trainers are very good at doing this. The great increase in road running over the last
twenty years has made this really important for the many amateur athletes who run
marathons and half marathons.
Physics of this Force x time of contact = momentum
change
For a given momentum change increase the time and you reduce the
force.
Now to trains.
Resistance in trains is due to the following factors:
(a)
friction in the bearings
(b) air friction outside the train – hence the streamlining of high
speed trains
(c) friction between the carriages and the track
Remember that
there is also the friction between the driving wheels of the engine and the track but without
this the train could not move along. It is therefore essential to motion and not a
problem.