This is more of a curiosity question rather than a homework question, and it has to do with how to relate the electrical motor torque to a vehicle's motion using Newton's Laws. Now for a vehicle (say RC car) moving forward in a straight line, the forces that are acting on it are the gravitational and normal forces, along with the rolling resistance and the force applied due to the rotation of the electrical motor. I can easily write the equation of motion here in this case where it's just the applied force - friction force = mass * accel However, another problem arises when I construct an FBD for the car's wheel. In the case for rolling without slipping, it is the friction force that causes the wheel to roll forward, but when rolling resistance is not negligible, I am not sure how that is shown on the FBD. There is also the motor torque now present in the problem. All I'm trying to do is relate the motor's torque to the applied force of the vehicle, and the approach I've taken is with the use of Newton's Equations of Motion.