## pressure, weight, density... perpetual motion?

Hello.

I've come up with an idea that I need to check:

There is a wheel, filled up with air, inmersed on a tank of water.

Attached to that wheel there is a number of boxes, that has two windows on opposite sides that can communicate with the water on the tank, or with the air inside the wheel.

Inside these boxes, there is a heavy plunger that keeps the water and air appart, and falls down to the bottom of the box due to gravity.

When it opens the window to the water, closes the air window, and viceversa.

So all the plungers on one side of the wheel closes the air window, and the plungers on the other side closes the water one.

So on one side of the wheel all the boxes are filled up with water, and on the other side all the boxes are filled up with air.

This represents a difference on forces, because the boxes filled up with air have a quantity of thrust, and the boxes with water have an adittional weight that the other boxes does not.

So you can see that the wheel have different forces on each side, due to the plungers falling down to the bottom of the boxes by their own weight, and letting the boxes on one side fill with air, and the other side of the wheel fill with water, as the wheel rotates... and you can see that this imbalance is always there (it doesn't matter that the wheel is spinning), and in fact, is this imbalance what is causing the rotation of the wheel...

So where is the error here?

I post an animation to clarify how it is supposed to work...
Attached Thumbnails

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 Also, i'm not saying that the air boxes floats on the water and rise up... i'm just telling that the resultant on one side is less than on the other, so it doesn't matter if all the boxes shrink or float... the only thing that matters is that the two sides of the wheel are not in balance.
 Recognitions: Gold Member Hi, Cala. Even in an ideal situation, with no friction or viscosity losses, the best that you could possibly do is break even. The instant that you try to extract any useful energy from the system, such as by attaching a pulley to run something, you lose.

## pressure, weight, density... perpetual motion?

Well, this setup has no other intention that try to run continuosly. If it can not do other work, I conform myself with this thing being running forever...

 I posted this thing also because I'm not able to find where is the mistake (...but hoping nowhere!). I post a picture of the forces as I see them, and the (more or less) resultant force, and imbalance on the torque. There are only two things that I see could go against the movement: - When the bottom box pass from be filled with water to be filled with air... Can the plunger (taking into account that is much heavier than the water) move the water outside the box? I think it is, but maybe i'm wrong... - The other moment that could avoid the wheel from spinning is when two boxes are on top and bottom of the wheel. In this situation, the two plungers of this boxes are on one side of the wheel... Could this extra weight compensate the imabalance?. I think that they can't, because there are a lot of other weights opposing (so maybe in this case, the imbalance is less than on other positions, but still it works). I would appreciate if you explain this better, or have other ideas on what could stop the device turning forever. Attached Thumbnails
 Recognitions: Gold Member Science Advisor Staff Emeritus If the plunger can push water outside the box, then it can also push air outside the box- where it escapes. So the next time the plunger pushes the water out of the box, where does the air to fill it come from?

Mentor
 Quote by cala There is a wheel, filled up with air, inmersed on a tank of water.
Hi cala, yes, the submerged wheel filled with air is an ever-popular source of failed perpetual motion ideas. The fundamental error of all such designs is ignoring the work done on the fluid in each cycle. Here is a good link on the subject: http://www.lhup.edu/~dsimanek/museum/themes/buoyant.htm

 Nice link DaleSpam, it's exactly the same thing i'm talking here... Ok, maybe (for sure) it doesn't work, But still there is something i don't understand: They say that, in order to get it working, the bottom box plunger has to rise water to the top box, doing the same amount of work than the buoyant forces do to turn the wheel. But if the plunger weights enough, this still could be done, right? I mean, a very heavy plunger (or dense material, think on the weight or density you want or need to do that) could expulse the water when the box is at the bottom of the cycle... Yes or no? If the answer is yes, then what is the problem? Gravity of the plunger will do the work of rising-up the water to let the wheel spinning, isn't it? We don't introduce work in any place...