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Please excuse my English...

Let's say we have a 10m x 10m x 10m water tank filled with water.

After a little search i found that the pressure on the sidings at 9-10m depth would be approximately -> 1 bar => 100 KN/m2.

Now let's assume that we sink 400 spheres with a diameter of 1m in the tank (100 every 1m of depth (with a surface of 10m x 10m = 10 m2))

and we've placed a funnel (with some holes on its sidings to "breathe") at the top, which guides the spheres into a (non airtight) tube 1m diameter.

The tube will then guide the spheres, outside and at the bottom, of the tank (at 9-10m depth).

If we assume that the spheres are made of steel 2mm thickness, their weight would be approximately 50Kgr, and their volume 500lt. So their buoyancy would be 4.5KN.

If the tube was already filled with spheres, i end up that the force at the exit point would be 4.5KN x 400spheres - friction => 1,800KN - friction.

I believe that the friction could surely be less than 1,700KN. Right???!!!

So if I'm right, the "force in" would be many times more the "force out" (pressure).

And if I'm right this could work everywhere even in a spaceship (through centrifugal)...

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Qmechanic
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Strike AU
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1 Answers1

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So if I'm right, the "force in" would be many times more the "force out" (pressure).

Nope. The energy required to submerge a sphere is the same as the energy you would gain by letting it come up again.

The tube doesn't help.

  1. You can push in the sphere from the top without a tube. Obviously the energy required is the same as the buoyant energy (as it's symmetrical).
  2. You could use a tube to bring the sphere to the bottom of the pool and than push it in through some sort of magic pressure barrier. However the pressure in the tube is a lot lower than the pressure in the water, so you would have to push in the sphere against that pressure difference. Energy required is still the same as the buoyant energy
  3. You could use some "lock" mechanism like canals with ships do. Drop the sphere to the bottom. Seal a chamber at the bottom of the tube. Let the water come in and then the sphere can just roll out. However, for the first sphere you need to spend energy to put in the tube and displace the water. For the second sphere, you would have to pump out the chamber against the water pressure. Both of these energies are significantly larger than the buoyant energy
Hilmar
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