Sensor: Potentiometer

Potentiometers come in all sorts of shapes and sizes from linear inputs to rotary inputs. Dimmer lights in a house use a potentiometer. A knob for tuning a car radio, the volume on an electric guitar,  or the temperature dial on an oven could also be made from a potentiometer. Look around your house to see if you can find an input that uses a potentiometer. 

Control knobs for heating/cooling system
Make a pencil’s lead potentiometer (Instructables)
Volume control