The phrase "saving energy" is slightly wrong, because energy is never lost; what runs out is the portion still usable. In a pendulum, kinetic and potential energy trade places while the total mechanical energy barely moves. A thermal power plant runs a far longer chain, from chemical to heat to steam to mechanical and only then to electrical, so long that most of the heat escapes up the flue and into the cooling water. Every conversion step sheds a little more, and the sum of everything shed is precisely the wasted heat.
The phrase "saving energy" is slightly wrong, because energy is never lost; what runs out is the portion still usable. In a pendulum, kinetic and potential energy trade places while the total mechanical energy barely moves. A thermal power plant runs a far longer chain, from chemical to heat to steam to mechanical and only then to electrical, so long that most of the heat escapes up the flue and into the cooling water. Every conversion step sheds a little more, and the sum of everything shed is precisely the wasted heat.
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