Why do lighter objects float and denser sink? I understand this from the perspective that if the object can displace the equal mass of water it will float, but I wonder from the perspective of gravity! How does gravity cause Archimedes' principle? It must be gravity, right, because in space Archimedes' principle doesn't work!
The ultimate question I need to answer is how all this force interplay causes density stratification. For example, how does gravity cause Earth to have a density gradient: the densest elements in the core, and the lightest in the crust?
Here's what I got from the comments so far. I though it should be a good starting point if someone wants to write an answer. It also can be totally wrong.
There is a pressure gradient inside a body of liquid along the depth gradient. It is caused by the fact that the distance between two objects is squared and inversely proportional to the gravitational pull (see the image below). The deeper water thus is attracted to the Earth stronger, and where there is a pressure difference, there is a force, the buoyant force in this case.
However, now I have even more questions than I used to:
- If there is a pressure gradient, why there's no flow in water along the depth gradient?
- What mechanism (or what part of the gravity equation) makes denser objects sink despite the buoyant force? Is it the mass? What about Galileo's experiment then? Doesn't it show that the effect of mass is negligible?