am i missing something obvious?

[Cherryman]

Even then, water can still slip between the bottom of the tank and the wood surface.  However, if you put a vertical wood rod through a correspondingly sized hole in the bottom of a water tank with just a little bit sticking out of the bottom, you'll see the wood rod drop through the bottom rather than float upward.

You stated when there can not come water underneath, there is no boyancy.

So i ask (theoretically)  If you have perfect smooth surface as a tank bottom and you press a perfect smooth  floating "something"  on it, it stays down?   

I would think there would still be buoyancy, i can imagine that there also will be vacuum or water pressure which can exceed the buoyancy, but that does not mean there isn't any bouncy..  ?

Its not an attack.. I just wondered .

[Comassion]

If you can indeed get two perfectly smooth surfaces that keep water from getting between them, then yes, you should be able to keep those two surfaces attached even if one of those surfaces belongs to an otherwise 'free floating' object.


Of note also is the fact that if you have two perfectly smooth surfaces touch, they will adhere to each other in any environment due to pressure - interestingly enough, even in a vacuum, due to pressure from virtual particles (The Casimir effect).


A more feasible way to see something like this in action would be to put a block of wood in the bottom of a dry tank, seal the bottom with some sort of watertight seal (though I'm not sure how to get a watertight seal that doesn't also otherwise attach the wood to the bottom - maybe you could use caulk, but not let it dry), and then fill the tank with water.  Even when the wood is submerged, as long as water can't get under the wood, it should remain on the bottom.

[Cherryman]

If you can indeed get two perfectly smooth surfaces that keep water from getting between them, then yes, you should be able to keep those two surfaces attached even if one of those surfaces belongs to an otherwise 'free floating' object.


Of note also is the fact that if you have two perfectly smooth surfaces touch, they will adhere to each other in any environment due to pressure - interestingly enough, even in a vacuum, due to pressure from virtual particles (The Casimir effect).

Now you mention it, i have heard of the Casmir effect indeed.

But my question remains..  Is there NO buoyancy, or do the "other" forces exceed the buoyancy?

[Comassion]

Now you mention it, i have heard of the Casmir effect indeed.

But my question remains..  Is there NO buoyancy, or do the "other" forces exceed the buoyancy?

There would be no upward buoyant force from the water, because buoyancy is effectively a type of pressure.  In order to exert said pressure on an object, the water has to be touching the object from the points at which it is exerting that pressure.  In the case we were talking about where you allow no water underneath your object, the buoyant force remaining (from the water above the object) is actually downward, and is holding the object against the smooth surface.

[Cherryman]

There would be no upward buoyant force from the water, because buoyancy is effectively a type of pressure.  In order to exert said pressure on an object, the water has to be touching the object from the points at which it is exerting that pressure.  In the case we were talking about where you allow no water underneath your object, the buoyant force remaining (from the water above the object) is actually downward, and is holding the object against the smooth surface.

Ok Tnx!