Friction

As you watch a train go by do you ever think about those spinning bearings on every axle? Traci does and posted a closeup a few days ago. Not so many years ago roller bearings were as rare as electronic braking is today. Instead there were bronze friction bearings contained in "boxes" like this full of grease. If the lubrication ran dry they got hot... hence the "hotbox" and the hotbox detector. If they got too hot the steel frame glowed red, the bronze melted and the whole thing came apart.

Friction bearings do still exist. This one is under a caboose (equally rare) on Alaska's narrow gauge White Pass & Yukon.