In a mechanical clock the spring is compressed by winding, it attains potential energy. The releasing of the spring slowly is the kinetic energy, using that the wheels of the clock turns, therefore potential energy is converted into kinetic energy. PE → KE → mechanical energy.
In the quartz clock, the electric cell gives, the electrical energy and it is converted into mechanical energy by which the wheels of the clock turns. Therefore the energy transformation is chemical energy → electrical energy → mechanical energy.
