An automatic watch is a mechanical timepiece that has a mainspring wound automatically due to the natural motion of the wearer's arm. This natural movement of the wearer provides energy to the self-winding watch to run without any manual winding required.
An automated watch or a self-winding watch consists of a rotor, or eccentric weight, that turns on a pivot. The natural motion of wearer's arm is translated into a circular motion of the rotor, which pivots on a staff that is connected to a ratcheted winding mechanism. Through a series of reversers and reducing gears, the rotor eventually winds up the mainspring.