Mistake
Kre,
You are completely right, in my initial intervention I stated that 1 Hz equals to one TURN, then instead of clarifying I wrote RPM instead of RPS. Sorry I made a MISTAKE..and I'm going to edit and correct this mistake right now. Thank you very much for your observation.
Returning to the point:
One Hz equals to one cycle per second, so 60Hz means 60 cycles per second. A cycle (electrical) is a series of variations in a determined electric parameter, in this case Volts, that periodically are repeated. Each set of different variations is known as a cycle.
In a sinusoidal voltage wave, produced when the windings of the stator are cut by the rotating field of the rotor, in a progressive way, there is an alternation in the N and S poles passing in front of the stator windings, inducting an altenating voltage in the stator.
This voltage starts from zero, when both poles are at 90° electrical degrees with respect to the magnetic axis of the stator windings, rises up to align the axis, again decreases down to zero and then the opposite pole, to say south pole, approaches to the same coil, generating the opposite voltage, following the same path but inverted.
As we can see there have been a series of voltage variations continuosly different: Zero, max positive, zero, max negative, zero. From this point the next variation is a repetition (zero, max positive) of the previous series. Here starts a new cycle.
An electrical cycle comprises a positive half wave and a negative half wave. The measurement unit is the Hertz = 1 cycle per second, 60 Hz = 60 cycles per second, but each cycle has a positive and a negative HALF waves as you can easily see in your oscilloscope. 60 Hz or cycles per second have 120 half waves, and of course 3600 cycles will have 7200 half waves.
KRE, I know that you are an expert in this field, but not only you read these lines, so I try to be didactic for many people interested in technical information, explaining in a very simple way electrical themes , hopping to be useful. Thanks for your attention.