Question by raghunc: How does a pantogram (the one above an electric train)sustain friction?
Answer by Craigory
I think you mean pantograph.
Anyway, they are spring-loaded so they maintain a specific upward contact force with the overhead wire. This force is controlled rather carefully so that the pantograph and wire are not damaged over the operating speed range of the vehicle.
For higher-speed applications, special measures are taken to tune the aerodynamics of the pantograph so that the up-force is optimized for high-speed running.
The contact surface of the pantograph (the shoe) is a carbon-based material, much like a carbon brush for a DC motor. This is the surface that wears, so it is changed periodically, in order to keep the overhead wire from wearing out.
What do you think? Answer below!