# Perpetua mobile theoretical misunderstanding

1. Aug 10, 2013

### joao_pimentel

Hello

I was patent examiner on the Portuguese patent office for 3 years and we have a lot of perpetua mobile applications, so I wanted to find now, the theoretical misunderstanding I'm missing here

Imagine you have a track (on a table, on the xOy plane) on which a metal ball would follow, and at a certain length of the track, there would be a tubular permanent magnet, that would create a force on the ball accelerating it. That ball would be accelerated every time it passes through the tube!

I know that there is some paradox on my lemma, but I can't find where

PS: Actually I know that the magnetic field is conservative, but something is missing

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2. Aug 10, 2013

### Staff: Mentor

The tube will not accelerate the ball around the track. I'm not sure what will happen inside the tube since the flux is so uniform, but once the ball leaves the tube it will be attracted right back to it.

3. Aug 10, 2013

### joao_pimentel

That's what I can't understand because every time I see images of magnetic field I see this

By the way, I know that the force is $$F=q(E + v\times B)$$

But how to relate the Force created by the magnetic field of a permenant magnet if the ball is stopped, v=0, and there is no Electric field

You said the ball would came back, but can't we shield the field, so the field just applies inside the tube.

Sorry, too many questions

Last edited: Aug 10, 2013
4. Aug 10, 2013