Hello everyone! In the following speed-torque characteristic of a DC shunt motor, we see that if the speed exceeds a certain value, then the machine becomes a generator. I don't understand something. How is it possible for the machine to have a negative torque and a positive speed? Shouldn't they always be of the same sign? For example if the machine (motor or generator) rotates clockwise, then speed and torque should be positive. So what does torque and speed of different sign mean?