Buff and draft forces are associated with which phase of operation?

Buff and draft forces are associated with which phase of operation?

• A. The aerodynamic drag on a moving train.
• B. The thermal expansion of rails.
• C. The horizontal and vertical forces generated during acceleration, braking, and coupling.
• D. The noise produced by wheels.

Answer: (C)

Buff and draft forces come from the longitudinal interaction between cars through the couplers as the train changes speed. When the train accelerates, the locomotive and front cars push on the rest, and the couplers experience a compressive load—buff. When braking, the inertia of the cars keeps them moving forward, pulling on the couplers and creating a tensile load—draft. During coupling, as cars come together, transient forces develop as the masses settle into motion with each other. In short, these are horizontal (with some vertical components from geometry) forces generated during acceleration, braking, and coupling. They aren’t about aerodynamic drag, which is external resistance to motion; nor about thermal expansion of rails, which is a material expansion issue; nor about wheel-rail noise, which is a vibration phenomenon.

Buff and draft forces come from the longitudinal interaction between cars through the couplers as the train changes speed. When the train accelerates, the locomotive and front cars push on the rest, and the couplers experience a compressive load—buff. When braking, the inertia of the cars keeps them moving forward, pulling on the couplers and creating a tensile load—draft. During coupling, as cars come together, transient forces develop as the masses settle into motion with each other. In short, these are horizontal (with some vertical components from geometry) forces generated during acceleration, braking, and coupling.

They aren’t about aerodynamic drag, which is external resistance to motion; nor about thermal expansion of rails, which is a material expansion issue; nor about wheel-rail noise, which is a vibration phenomenon.