Hi. When I took AP Physics last year, my teacher demonstrated the power of pressure by this object. It looked like a lid. It was rubber. You put the lid on a wooden desk, turn the nod on top of the lid, and try pulling the lid off the desk without sliding the lid. I forgot the name of this object. Does anyone know what it's called? I was thinking about it one night and I think I have the right concept. Correct me if I'm wrong. When you turn the nod, everything between the wooden desk and top of the lid becomes a vacuum; thus, it has no pressure. When you draw a force diagram on the lid, there is a force acting down: F= P * A (neglecting the weight of the lid). There is no force acting up because there is barely any pressure. Therefore, it is extremely difficult to pull the lid off the table. Is that correct? Thanks in advance!