required to dislodge the wheel from the axle seat is much greater than that required to mount it.
Let's assume that the wheel and axle units we have developed are now ready to be placed into service.
They are placed on units called trucks, the general term covering the assembly of parts which, as whole
structures, support a car body at each end. In the next chapter you will see how they are added to the car truck
and how the truck is constructed to distribute the weight of the car and its contents to the axle journals, to the
wheels, and finally to the rails.