# Fluid Statics-hollow cylinder problem

If a hollow cylinder(something like a plastic cup)is partially submerged in water, am I correct in thinking that the only three forces acting on the cylinder are the buoyant force, the weight of the cylinder and the force exerted by the air at the water air barrier in the cylinder? Also is the resultant force due to the pressure distribution acting on the container and the air within it the buoyant force subtract the force a due to the air pushing at the air water barrier(inside the cup). The cylinder has a column of air inside it, so I thought the buoyant force would push against the air in the cylinder, and the force would be equal to the volume of water displaced. The height of the water is at a distance d below the water level in contact with the atmosphere.

• by a hollow cylinder do you mean a plastic cup with the bottom cut off? Or just a plastic cup 'as-is'? – mogelbuster Oct 25 '16 at 23:13
• Hi a perfect cylinder that you could fill with water to drink out of(usual hole in the top so you could drink out of it), but upside down and in equilibrium within the water. – G2357 Oct 26 '16 at 5:12