What is one of the key factors influencing rotational speed in a motor?

Line frequency is a fundamental factor influencing the rotational speed of an electric motor, particularly in alternating current (AC) motors. This is because the speed of these motors is directly related to the frequency of the electrical supply. In synchronous motors, for example, the speed can be calculated using the formula:

[ \text{Speed (RPM)} = \frac{120 \times \text{Line Frequency (Hz)}}{\text{Number of Poles}} ]

This relationship illustrates how increasing the line frequency leads to an increase in the rotational speed, given that the number of poles remains constant.

For induction motors, while the actual speed may be slightly less than the synchronous speed due to slip, the line frequency still establishes the baseline maximum speed. Thus, control of line frequency can be a method to regulate the motor's operational speed.

The other factors, while impacting motor performance, do not have a direct, mathematical correlation with rotational speed in the same fundamental way that line frequency does. For instance, the diameter of the rotor can affect torque and inertia but does not change how speed is derived from line frequency. Temperature can impact efficiency and function but does not set the speed itself, and lubrication type primarily affects wear and efficiency rather than the speed at which