# Opinion needed: 'friend's' idea

#### vincentm

Gold Member
A 'friend' of mine has proposed an idea on how to achieve energy, to me it kinda sounds like perpetual motion but not too sure. Anyways here it goes;

Instead of damming up a river to create a resevoir we would use a recirculating system of water. There would be a resevoir of water but it would be a closed system. The only problem I encountered was being able to pump the water to the top after falling and turning the turbine generators. The solution is to use bouyancy. Air is lighter than water. Using this principle we could build a series of water pumps. These would use air pumps to inflate or fill rising and falling balloons or ballasts to generate power needed to bring the water back to the top. There would need to be quite a few of these in the resevoir to pump the correct amount back to the top. The other thing that is good is that these ballasts would be attached to columns. During the rise and fall the ballast systems would also create energy as well as turn turbines for the pump system. They would use magnetic cogs instead of mechanical ones. As it rises magnetic teeth would turn cogs within a casing as the ballast system rises. When it reaches the surface there will be an interlocking of the top sort like a soket plug for the exchange of electricty. With these principles there many ways to build it. That in conjuction with solar power, lunar power(The use of tidal forces and ocean waves to turn turbines) The energy would be virtually free. Meaning that the only cost would be regular maintanence.

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#### Q_Goest

Homework Helper
Gold Member
Hi vincentm, You're right, this is a perpetual motion machine which needless to say, won't work.

~ On a side note:

Just a thought for everyone: It seems we get a lot of perpetual motion machine ideas here. Maybe instead of entertaining them in the engineering forums, they could be placed either in the "Skepticism and Debunking" forum, or better yet, make a subforum to that one specifically for perpetual motion machines.

I'm also thinking that if a subforum was created, a sticky could also be created that listed web pages that tried to con people using perpetual motion machine ideas. At least then, PhysicsForums might serve a benefit to folks looking to 'invest' in such grand schemes. Most perpetual motion machines are obvious to an engineer, but not to folks without a background in engineering or physics. Putting up a web page exposing fraudulent web sites and explaining why they are fraudulent might be fun to boot. Members here could also post new web sites by name and expose them. There are plenty of fraudulent web sites out there to expose!

#### HallsofIvy

Homework Helper
Your 'friend' seems to think that because air is lighter than water, it would require less energy to inflate the balloons which push the water uphill. That's wrong. The energy needed to inflate a balloon is the energy necessary to stretch the fabric of the balloon. If you, say, set a book on top of a balloon and then tried to blow up the balloon, the energy required would be that plus the energy required to lift the book. Here, the energy required to inflate the ballons would be the energy required to lift the water (plus whatever energy your "columns" were delivering) plus the energy need to stretch the balloons themselve. Even without considering energy loss through friction in the air pumps, this system requires more energy than is gained from the water flowing downhill.

#### Gokul43201

Staff Emeritus
Gold Member
These would use air pumps to inflate or fill rising and falling balloons or ballasts to generate power needed to bring the water back to the top.
Your friend will have to expend at least as much energy in filling these balloons (i.e., getting the highly buoyant air under water) as s/he will get from them rising up through the water.

Energy needed to fill balloon=pressure* change in volume
$$=P(water) \cdot V(balloon)$$

Work done by balloon = buoyant force * distance
$$=\{\rho (water) \cdot V(balloon) \cdot g \}~\cdot h = \{ \rho (water) \cdot g \cdot h \} ~\cdot V(balloon) = P(water) \cdot V(balloon)$$

Therefore, energy used to fill balloon = energy gained by rising balloon.

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#### linux kid

I'm surprised your thread is still up. They mercilessly smothered mine and sent me a warning for referring to perpetual machines.

#### FredGarvin

The attempt is being made to educate the OP on the reasons why this is not a feasible idea. I am sure that if the OP comes back and indignantly protests that this could work and yet provides no supporting facts, then yes...this thread will be closed.

#### linux kid

The attempt is being made to educate the OP on the reasons why this is not a feasible idea. I am sure that if the OP comes back and indignantly protests that this could work and yet provides no supporting facts, then yes...this thread will be closed.
Well I never even suggested PMMs were possible. I only referred to them and my thread was closed. It is just ridiculous what some of these trigger happy mods are doing on this forum.

#### russ_watters

Mentor
And there we have it...

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