Active vs passive sensors

A passive sensor might be preferred because passive sensors generally require less energy than active sensors. Active sensors use more energy because they have emitters that send out their own signals. Passive sensors do not have emitters and do not need to send out their own signals, so they use less energy.

Potentiometers

Potentiometers are passive sensors, because they simply detect the change in resistance caused by a knob being turned or a slider being pushed. They do not need to send out their own signals, so they do not have emitters, so they are not active sensors.

Stretch receptors

Resistive position sensors are kind of like the stretch receptors in human stomachs, because both types of sensors can be used to avoid damage. Resistive position sensors detect the amount of tension in a material. A robot could use these sensors to avoiding bending any of its parts too much. This is like the stretch receptors in human stomachs because they sense how stretched our stomachs are and we can use that information to avoid overeating and bursting our stomachs.