"if you are confused by that..." YES YES I AM,(reply>), @Karthik T actually, from a physics perspective, they are identical. there are things called symmetries in physics, which basically say that physics doesn't care much about the state of the world around it, it will operate the same way here as it will 10 feet to the left. physics doesn't care if you rotate the screw or the cylinder, it will provide you the same ultimate result, stuff moves upwards. the symmetry is maintained, the universe doesn't care if the screw is spinning or if the world is spinning around the screw.<br><br>however, the other, subtler effects mean that while this gets the same ultimate result, the details change slightly, making this version of the screw lift more efficient and easy to maintain.,(reply>), Mohammed Avdol!,(reply>), @Karthik T Actually, I think it is fair to call it that - with a regular screw, you need some kind of casing and the screw forces the things you're lifting against the casing. In this case, the casing forces it against the screw, so it's just the other way around, as you'd expect.,(reply>)," Think of the screw as a spiral staircase. The scoops at <a href=""https://www.youtube.com/watch?v=-fu03F-Iah8&amp;t=4m55s"">4:55</a> force grain (or whatever) into the bottom of the staircase and continue feeding more in", so the grain has nowhere to go but up!,(reply>), @Panga exactly.. It's the scoop that makes this work.. So it's not fair to call rotating the cylinder the same as rotating the screw.. As Tom did