iPod click wheel

The wheel allows a user to find music, videos, photos and play games on the device.

The click wheel's design is credited to Apple's senior vice president of worldwide marketing, Phil Schiller.

It allowed the pitch and volume of the instrument to be controlled by the distance from the musician's hands to two antennae.

When a voltage is placed upon two conductors in close proximity with one another, without coming into contact, energy is stored in the form of electric fields.

So instead of passing through the plastic, the current creates a charge at the closest location to the finger, which is also known as capacitance.

Whenever the controller senses a change, it sends a signal to the microprocessor, which performs the desired action.