Replies

It is only no hard because there is air under it. Set it in a very thin layer of water and try that again. Hard. Now try it in a large tub of water. Easy again. He is not confusing the two. The difference is that solids and near solids don't transmit pressure the way true fluids do. Setting something on the floor does not relate since there is not viscus boundary to crate a suction when you pull it up. What do you think the force of a suction is except the pressure of standard atmosphere pressing down. A suction cup (or section of wall sitting in a thin puddle of water) could be pulled up with less force if it was at high altitude. It is the pressure difference between the out side and the inside. Any time you create a viscus boundary around the base of an object sitting in a flat solid you create a suction situation where the ambient pressure can't equalize between the object and the surface and that pressure will reside .separating the two (with the help of a tiny viscus force)