My questions is about the bar (not specifically) in this video: I want to know from somebody who has a better mechanical perception than me why the bar has the effect of wobbling back and forth. I think it's because the center of the mass of the system (not including the person) is low and if the bar is a little forward or back it produces torque, and it seems that the lower the center of mass is, the more torque/angular acceleration is produced. Is this because r in [itex]\tau[/itex] = F [itex]\cdot[/itex] r is higher? But if the center of mass is lower, doesn't that make the moment of inertia higher so [itex]\alpha[/itex] would be lower with the same torque? Or is it negligible because the bar weighs 5.4 lbs? The reason I think so is because I have done this with a 45 lb. bar and it wasn't that unstable. The biomechanics part of my speculation is to which muscles it really stabilizes. Because it's so wobbly, I think the muscles to push it over your face and over your stomach both have to be contracted so it stays in line. Which muscles would that be? I really just want to discuss this, especially the moment of inertia, torque, angular acceleration part of the effect, with people so discuss with me please.