Hi All, Recently we've been working on the distinction between the Eulerian and Lagrangian approaches in Fluid mechanics. I understand the simpler examples like a running stream of hot water etc. However one example is really tripping me up. So what's confusing me is that in analyzing water waves in a sea, the Eulerian and Lagrangian descriptions (incidentally) look the same i.e. they both trace a circle. Where I've been learning about this is this video (link below) by John Lumley from Penn State university : https://www.youtube.com/watch?v=mdN8OOkx2ko&list=PL0EC6527BE871ABA3" I thought that Eulerian approach is just looking at something from a fixed reference frame (which might be moving at a constant velocity)...sort of like a control volume analysis. However that doesn't explain this example. So I'm thinking maybe in Eulerian description instead of fixing a spatial reference frame, its more like fixing a slice of fluid...does this sound right?