Rail Vehicles
In order to start a train and accelerate it to a given speed, the locomotive(s) must develop sufficient tractive force to overcome the train's drag (resistance to motion), which is a combination of inertia, axle bearing friction, the friction of the wheels on the rails (which is substantially greater on curved track than on tangent track), and the force of gravity if on a grade. Once in motion, the train will develop additional drag as it accelerates due to aerodynamic forces, which increase with the square of the speed. Drag may also be produced at speed due to truck (bogie) hunting, which will increase the rolling friction between wheels and rails. If acceleration continues, the train will eventually attain a speed at which the available tractive force of the locomotive(s) will exactly offset the total drag, causing acceleration to cease. This top speed will be increased on a downgrade due to gravity assisting the motive power, and will be decreased on an upgrade due to gravity opposing the motive power.
Tractive effort can be theoretically calculated from a locomotive's mechanical characteristics (e.g., steam pressure, weight, etc.), or by actual testing with drawbar strain sensors and a dynamometer car. Power at rail is a railway term for the available power for traction, that is, the power that is available to propel the train.
Read more about this topic: Tractive Force
Famous quotes containing the words rail and/or vehicles:
“For this is the mark of a wise and upright man, not to rail against the gods in misfortune.”
—Aeschylus (525–456 B.C.)
“Television programming for children need not be saccharine or insipid in order to give to violence its proper balance in the scheme of things.... But as an endless diet for the sake of excitement and sensation in stories whose plots are vehicles for killing and torture and little more, it is not healthy for young children. Unfamiliar as yet with the full story of human response, they are being misled when they are offered perversion before they have fully learned what is sound.”
—Dorothy H. Cohen (20th century)