[Keelbuster]

Originally Posted by GreyOctober

due to its molecullar structure the pessure always exerts forces equally

this answer is vague; it doesn't contain enough information to aid your argument.

Originally Posted by GreyOctober

Sand is not a liquid. It might flow but it has different physics. It becomes a fluid and gains fluid properties once mixed with water.

sand is approximately liquid - it's a group of particles in close contact - H20 are smaller particles. Sand is an extreme example to show that the direction of earth's pull with induce an asymmetry in 'pressure' that is exerted on the surface of a submerged body. It works for solids too - I have a feeling that's why the depths under earths crust form layers (of MAGMA moohaha). But they don't rule out 'omnidirectional' pressure. Finally, mixing sand with water is not relevant here.

Originally Posted by GreyOctober

As with the forces acting on a body burried in sand for example, the forces are omnidirectional but NOT equal and indeed the greatest force acting would be gravity.

I think we need to lose the omnidirectional thing. Forces acting on the body in sand would be applied over its entire surface area, as it is in contact with particles on all sides. 'Omnidirectional' is vague. Gravity induces a gradient for an increased vertical force relative to the horizontal plane. Here we agree. But because i don't know why you see such a strong disanalogy between sand and water, i'm not sure why this doesn't convince you that at least _some_ measureable asymmetry in water pressure per surface area would be found associated with the vector that points away from the center of the earth. I'm really sure there is. There has to be. The question is how big it is. You seem to believe that it is negligible.

Originally Posted by GreyOctober

The object with the best pressure tollerance is a sphere. Some of the modern ocean explorers have pressure hulls in form of a sphere. The cillinder has also a very good pressure tollerance and since WWI they had this shape. Remember that pressure difference occurs between a medium (water) and a cavity with a different pressure. There is no presure difference between water and lets say the external hull of the submarine for example.

this part is fine with me. It's a little aside the main argument. I believe that the sphere is the best form to resist forces from all sides. That is because it is a shape with perfect symmetry. It is _also_ the best form to resist asymmetrical forces. But this is a (direct?) consequence of being optimal in the symmetric situation. Assymetrical forces are a subset of all forces that may be applied (someone please challenge this claim - i'm a little uncertain about it). The same can be said for the cylinder-like form used in the submarine (it is circular with respect to the XZ plane (where X is across the width of the sub and Z is up and down). The circle is optimal for resisting force applied at any point along its circumference, but also, (in?)directly as a consequence of being the best solution to this problem, the circle is also optimal for resisting asymmetrical forces (like earth's gravitational field).

I still disagree with you. You need to convince me that the disanalogy between sand and water is vicious. But even still I'm next to positive that there is an asymmetry in water pressure along the principal axes.

This is fun.



Kb