h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

i take what you and gnomon have said about solid wheels and friction on board. assuming the wheels and tracks were non deformable solids, the theoretical friction would be zero...correct?

i seem to recall that the point of contact between a perfect circle and another surface is a paradox of some kind.

this is actually quite interesting stuff to know and explains why trains use solid wheels, and why rolling stock is limited by the inclines it can travel and why salting of tracks is necessary in icy or wet weather.

also has me questioning the value of maglev rail systems.

Surely the friction can't be zero, because the friction is what is pushing the vehicle forward?

in practice it isn't. one site i read gave the energy loss from friction for trains as about 20%. as gnomon pointed out much of this would be on the various bearings, rather than the wheel contact surface.