May I suggest a simple experiment? Get a large ,shallow dish and fillit with water from a measuring-jug. You will now have a "full tank"
now tilt it.....water will slop over the edge.....continue tilting, until the bottom is exposed on the "high " side HORRORS! - your tank is empty, you can see the bottom.....OK, now level your dish again. SURPRISE!
It wasn't empty, at all. there is now a layer of water across the whole bottom.
Does this sound familiar?
I sometimes wonder just how some people manage to pass their PPL with such a poor grasp of elementary mechanics and physics.