Why would a speed reducer be used in a power transmission system?

A speed reducer is primarily used in a power transmission system to increase torque. When the rotational speed of a motor is reduced, the output torque is increased because of the relationship between torque, speed, and power. According to the equation of power (Power = Torque x Angular Speed), if the speed decreases while maintaining the same amount of power, the torque must increase.

In applications where high torque is needed at low speeds, such as in heavy machinery or conveyor systems, a speed reducer is essential. It ensures that sufficient force is transmitted to perform the necessary work without overloading the driving motor.

The other options do not accurately reflect the primary function of a speed reducer. While reducing friction may be a benefit of an optimized system, it is not the fundamental purpose of using a speed reducer. Increasing speed contradicts the very function of a speed reducer, which is to decrease speed. Enhancing thermal efficiency, while a desirable aspect in system design, is not a direct function of speed reduction, as thermal efficiency pertains to the management of heat generated rather than torque conversion.