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 works by moving water (or other fluid) from high potential energy to low potential energy, but by going through a *higher* state on the way. Gravitational potential energy is directly proportional to height, so we can just go with height = energy.

The core reason siphoning works is that at the highest point of the siphon, the energy gained by a unit of water going to the lower container is more than the energy required to lift another unit of water from the higher container up to the top.