A rheostat is a type of variable resistor. It is made up of a resistor element and a sliding contact that moves along the resistor element, increasing or decreasing its resistance. The most common type of rheostat is the potentiometer, which is used to control the volume on a radio or a speaker system. Rheostats can also be used to control the current in a circuit, regulate the speed of motors, or set the temperature on a stove. Rheostats are used in a variety of different electronic devices, from audio amplifiers to industrial equipment.