How can you control the speed of a DC motor?

Varying the voltage supplied to a DC motor is the key method for controlling its speed. When the voltage is increased, the current flow to the motor also typically increases, resulting in a higher speed of rotation. Conversely, reducing the voltage decreases the current and consequently the motor speed. This principle is foundational in electric motor control, as it directly impacts the torque and speed characteristics of the motor.

In contrast, altering the size of the motor, changing its weight, or adjusting the motor's diameter does not provide a practical or efficient means of controlling speed. These factors may influence overall performance or capability but do not enable direct speed adjustments in the same way that voltage manipulation does. Understanding this principle is crucial for effectively managing DC motors in various applications.