I am trying to understand physics, aerodynamics, and density, and their effect on load and force. I have a variety of barbells and plates. The barbells vary in length (4ft - 5 ft) and the plates vary in density. I recently purchased the Les Mills barbell and plate set, and those plates are larger and sand-filled versus my other plates which are smaller and solid iron(?). I loaded both barbells to the same weight, even tested on a scale. There was a 1.4 pound difference, but the larger, less dense plates "felt" significantly lighter to lift than the smaller more dense plates. I also notice than when the same weight is loaded on a longer barbell and the weight is distributed further apart, the load seems easier to lift. My question is whether the force my muscles use to lift the weight is less since the weight "feels" lighter, despite the actual scale weight being the same. So are muscles worked to the same degree if the weight being used is the same, but the load feels easier do to the aerodynamics and density? I notice the same thing with two different sets of 8# dumbbells. One is coated and shaped slightly smaller and the other is iron hexagon. In this case, the iron hexagon feel lighter since it is 1.75" longer.