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> In your toy system a stone that stays still (DC) would have no power (potential energy).

This is false. In the toy system, weight is current, height is voltage. A stone that stays still has constant voltage, not zero voltage. Thus, it would have a 'power'.

What the system lacks is to define the stone as a capacitive load. Then it would sorta make sense.

It is a hypothetical system, so you can only reason about the aspects the author defined. Tying potential energy in the toy system to real-world potential energy doesn't work.

(Btw, potential energy is not power, it is work. Power is work over time.)

> As a matter of fact the average DC power does not depend on frequency.

Uhm. "DC power" stops existing if the frequency ≠ 0, so in that sense it does depend on frequency.

It's true that power itself is not frequency dependent. However, any load is, as reactive losses (parasitic or not) are a function of the frequency. As the power is a function of the load, power ends up being directly tied to the frequency.

(A resistive load cannot exist outside of a perfect DC system, so reactive loads will exist).



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