Buff forces are?

Buff forces are?

• A. A term used to describe compressive coupler forces in a train that bunch the slack.
• B. A term used to describe tension coupler forces that stretch slack.
• C. The aerodynamic drag on the train.
• D. The friction between rails and wheels.

Answer: (D)

Buff forces are the compressive loads that travel through the train via the couplers when the train is pushed together during propulsion or braking. The force that creates and transmits this compression comes from the wheel–rail interaction: the friction at the contact between wheel tread and rail provides the traction that moves the train, and the reaction to that traction is carried along the train as a forward push on the cars, showing up as buffing (compressive) forces in the couplers and buffers. This makes the friction between rails and wheels the fundamental mechanism behind buff forces. The other descriptions describe related ideas that don’t define buff forces as the load mechanism: compressive or tensile actions in a way that emphasizes slack behavior, or aerodynamic drag, neither of which capture the load transfer produced by wheel–rail friction.

Buff forces are the compressive loads that travel through the train via the couplers when the train is pushed together during propulsion or braking. The force that creates and transmits this compression comes from the wheel–rail interaction: the friction at the contact between wheel tread and rail provides the traction that moves the train, and the reaction to that traction is carried along the train as a forward push on the cars, showing up as buffing (compressive) forces in the couplers and buffers. This makes the friction between rails and wheels the fundamental mechanism behind buff forces.

The other descriptions describe related ideas that don’t define buff forces as the load mechanism: compressive or tensile actions in a way that emphasizes slack behavior, or aerodynamic drag, neither of which capture the load transfer produced by wheel–rail friction.