In practice, gears do have inertia and friction between the coupled gear teeth that often cannot be neglected. An equivalent representation of a gear train with viscous friction, Coulomb friction, and inertia considered as lumped parameters is shown in Fig. 4-23, where Tdenotes the applied torque, T and T2 are the transmitted torque, FcX and Fc2 are the Coulomb friction coefficients, and B and B2 are the viscous friction coefficients. The torque equation for gear 2 is