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Forces on wheels and fuel consumption in cars

Authors: J. Güémez, M. Fiolhais

Ref.: European Journal of Physics 34, 1005-1013 (2013)

Abstract: Motivated by real classroom discussions, we analyze the forces acting on moving vehicles, specifically friction on their wheels. In typical front-wheeldrive cars when the car accelerates these forces are in the forward direction in the front wheels, but they are in the opposite direction in the rear wheels. The situation may be intriguing for students, but it may also be helpful and stimulating to clarify the role of friction forces on rolling objects. In this paper we also study the thermodynamical aspects of an accelerating car, relating the distance traveled to the amount of fuel consumed. The fuel consumption is explicitly shown to be Galilean invariant and we identify the Gibbs free energy as the relevant quantity that enters into the thermodynamical description of the accelerating car. The more realistic case of the car’s motion with the dragging forces taken into account is also discussed.

DOI: 10.1088/0143-0807/34/4/1005