Hi I'm in grade 11 physics and my teacher assigned a question where he asked "What does a bathroom scale measure? Explain you're reasoning" Ok for this I would say it measures normal force, according to newton's 3rd law you apply a force on the scale it exerts a force back on you and that is what it's measuring. The next part of the question is "Explain how you know it is not measuring mass and/or weight" It's not measuring mass because mass remains constant even in outer space but the scale reading changes even if you move your arms around while standing on it (air friction I guess?) and if you redirect your force that you're putting on it, like step on the scale and hold something at the same time. Also because of the same reasoning it's not weight because weight is just the force of gravity.......(?) Thats all, am I on the right track? What is exactly is weight? And mass? We never had a definition for mass in class, it was just, the amount of "stuff" and there is no real way to measure mass..... Any help would be appreciated.