This is a video tutorial of DC motor control. This video shows how to control the DC motor speed. In this video, speed of the DC motor is controlled by changing the power supply. Increasing speed can be done by increasing the voltage, and decreasing the voltage will decrease the speed of DC motor. Here is the video :

To control the voltage, we can use the voltage regulator with potentiometer. The linear amplifier is used to change the linearity of DC voltage. Beside that, we can also control the speed of DC motor by using PWM.