Thus the diagram shows the tractive force at any instant.
Moreover, the average tractive power per locomotive and the average capacity per freight car advanced greatly in this period, although specific figures cannot be given.
There are certain fundamental relations common to all tractive problems, and these are briefly considered in §§ i and 2, after which the article refers particularly to steam locomotives, although §§ 4, 5, 7, 8, 9, and 10 have a general application to all modes of traction.
The fundamental condition governing the design of all tractive machinery is that the wheels belonging to the axles to which torque is applied shall roll along the rails without slipping, and exert a tractive force on the train.
The fundamental relation between the applied torque and the tractive force F will be understood from fig.