Calculate the Force Needed to Move a Railroad Car

• 1). Determine the coefficient of friction between the car wheels and the rail. This coefficient (μ) can either be selected theoretically from a table, or it can be measured experimentally. The coefficient of rolling friction is much lower than the coefficient of static friction, which would apply if the wheel were not allowed to rotate and would have to slide. The coefficient of rolling friction for a wheel-rail interface is approximately 0.001, while the coefficient of static friction for a steel-on-steel interface is approximately 0.5. Therefore, it requires far less force to move a rail car with freely moving wheels than one with the wheels locked.
  
  
• 2). Determine the friction force (F) that the rail car has to overcome to move. The friction force is based on the following formula: F = μW, where μ is the coefficient of rolling friction between the wheel and the rail and W is the weight of the rail car. If the weight of a fully loaded rail car is 280,000 pounds, then F = (0.001 x 280,000) = 280 pounds.
  
  
• 3). Because the only horizontal force that the railroad car produces is the friction force, the force to move the rail car (P) is equal to the friction force (F). Therefore, using the previous example, an input force of 280 pounds is needed to move the rail car.