That perpetual machine on the tubes

[Lil' Lavery]

While I (mostly) understand why he says it works, I'm not very good at explaining it. Try jumping around wikipedia (and reading the sources) to get some idea.
http://en.wikipedia.org/wiki/Perepiteia
And to explain why it does or doesn't work, we can simply use the fact that our concept of time may be broken (and thus making it impossible to measure power ).