Why must there be some friction between train tracks and train wheels?
Why must there be some friction between train tracks and train wheels? The friction between the wheels and rails occurs in the wheel-rail interface or contact patch. The traction force, the braking forces and the centering forces, all contribute to stable running.
How do trains have enough friction to move?
Their wheels are made of steel, being pressed hard against the steel of the railway. As they press against each other, some of the molecules in the wheels bind to the molecules of the rail. This is the reason they have traction — what I assume you meant by “friction”, which is essentially the same thing.
Can a train slip off the track?
Slippery rail, or low railhead adhesion, is a condition of railways (railroads) where contamination of the railhead reduces the traction between the wheel and the rail. This can lead to wheelslip when the train is taking power, and wheelslide when the train is braking.