@Graham: But a car does jerk backwards when you hit the brakes. The wheels stop first; the chassis still has momentum. The chassis overshoots and is pulled back.

@cmaster-reinstatemonica: I think you may have switched around even / odd. The even harmonics have a node in the middle and are suppressed. You get the fundamental, 3rd, 5th, etc.

@StephenSwensen: In mathematics there is a theorem called Gödel’s incompleteness theorem that implies that you can’t find a “complete” set of axioms which you can use to prove all things that are true. In science, it is theoretically possible but unknown whether there is some fundamental set of laws that we could discover that explain the behavior of the universe in exact detail.

@JanDvorak: DC still still uses multiple conductors, no charge accumulates.

"...if they stand closer together than 1 m there will be no destructive interference anywhere." This is incorrect, because it assumes that the people are singing in phase, which is not generally the case.

@PatrickM: The kind of velocity you would want to get from a comet would be in the km/s range. The harpoon would need to be made out of some very sturdy stuff. Imagine trying to harpoon a fighter jet as it flew past you.

The electron is moving backwards in this scenario: work is actually done when the electron is moved from the +1V plate to the 0V plate. When the electron is moved from 0V to +1V, you can harness its movement to do work elsewhere (but less than 1eV, due to inefficiencies).

I'd like to note that you can see the two parts of a typical white LED here: the blue spike is the LED itself, and the green-yellow hump is the phosphor which absorbs blue light and emits green-yellow.