I understand that an object, say a closed plastic cube full of air, stuck to the bottom of an aquarium with a smooth glass bottom will not float if you firmly place it such that no water can get underneath. What if you change the shape such that you add surfaces that water CAN get under to provide lift? Take the cube and change it into a T shape for instance. Now the horizontal part at the top DOES have area under which water can provide lift. Will this break the suction holding the bottom of the T to the bottom of the aquarium and cause it to float?
let's annotate the following
- m = weight of the object
- H = height of the object's flange
- D is the depth of the water to the top of the object
- rho.g.D is the pressure of water on the top
- rho.g.(D+H)= the pressure on the bottom of the flange
- L= width of the object
- we assume the thickness of the object as 1 for now.
The trapezoid areas of the pressure on the sides cancel out.
when $ \rho.g.(D+H)2B \geq m+\rho .g.D.L$ the buoyancy will float the object.