# Why should or shouldnt this work?

## Main Question or Discussion Point

I know perpetual motion is something that scientists have been trying to manage nearly since the beggining of times. I know it is actually imposible to manage it under the (actual)laws of thermodynamics, but i have been thinking of something that apparently would work.

http://img2.imageshack.us/img2/2219/99126full.jpg [Broken]
The black ball, would be ferrofluid and the grey/blue thing bellow would be a neodimiun magnet, which would keep the ferrofluid in that position. The grey ball would be less dense than the ferrofluid so it would float (the white arrows) and once it arrives to the maximun height it would fall due to gravity (black arrows).

Well taking all this into account we may think that the ball may move for ever but that is actually imposible under the actual thermodinamics, so I would like to know why wouldnt this work or if i won´t have to pay for electricity again:D

PD:sorry for my bad english i´m not a native speaker and im only 16 xD

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HallsofIvy
Homework Helper
Why would it "fall due to gravity" at that point? What happens there that wasn't happening before? And once it has fallen, why should it then go back up? There is the same force of gravity on it on the way up that was on it on the way down.

well, the ball would be less dense than ferrofluid, so it would float and consequently go up.
It will fall in that point because the inertia(i think its written like this) will throw the ball out of the ferrofluid and stopping the flotation, it will fall. This is what I think should happen but I´m not a physicist and thats why I ask you :D

a greater force than the ferrofluid provides would be required to shove the sphere into the fluid at the bottom. Do you understand what I mean?

Mm... so the higher the ball gets the more energy is required to shove the ball into the ferrofluid?(because the ferrofluid is higher too)

Assuming that the ball is able to enter the fluid it will float to a point close to the tip of the second white arrow and there it will stay some of it still submerged and at a position such that its weight is balanced by the upthrust of the liquid..The main flaw in the design is that energy will be needed to push the ball out of the fluid.

russ_watters
Mentor
A ferrofluid is formed into that shape precisely because it has a magnetic field supporting it. It isn't behaving like a normal fluid and so you can't apply normal fluid mechanics to it (in this case, pressure and buoyancy). Applying inapplicable principles yields the contradiction you have found.