A clear picture of the principal of the pulse motor.
The researcher pushes the weight which will slowly start to move, by pushing it again it will go faster, as you can imagine the weight will continue to swing for some time.
By attaching a magnet and moving the weight over a coil energy is extracted. The energy generated is far greater as that what the researcher can generate.
The mass accelerates and decelerates, the amount of energy in the system is related to the speed and the mass. The push scales in that exact same way.