Quote:
Originally Posted by Chris K
I had a discussion once with an EE about my inability to understand alternating current and how do you get any work done with electrons having a net movement of zero. He said "you're not turning a paddle wheel with it. You're doing work. Think of sawing a board with a hand saw. The net movement in the saw's reciprocation is zero but the work and its movement is down through the board. Now I don't know if that's a ubiquitous explanation of AC in the EE world but it was a revelation for me!
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Yes, part of the analogy is friction (in the case of the saw) or resistance (in a circuit).
If instead of a saw going back and forth, you had a pendulum in a vacuum with a frictionless pivot, it would go back and forth forever without losing any energy.
The action of the frictionless pendulum is transfer of energy between potential and kinetic forms - the pendulum at the top of its swing has potential energy, and at the bottom of the swing that has been exchanged for kinetic energy. The electrical analog is an LC circuit with an oscillating current. At one point of the cycle the electrons have maximum potential energy (voltage on the capacitor) and at the other part of the cycle they have maximum motion (current in the inductor).