why would the siphoning effect not be perpetual motion?

Question

My coworker is telling me that perpetual motion exists and shows me a video of a guy using the siphoning effect on some water cans.

I’m telling him that perpetual motion, physically, cannot exist.

But why would it not work?

In: Physics

Answer 1

Siphoning only works if your target is at a lower elevation than your source. Or, more expressively presented, if the fluid column going *down* is heavier than the fluid column going *up*. It basically borrows a bit of potential energy from the fluid going down the bend and uses it to lift the intake fluid over the bend. It’s very much the same thing as throwing a long bit of rope over a pulley down into a basement and watching it spool up the pulley and down in the hole from its weight.