If mass and weight are different, why does it seem the kilogram is used interchangeably for each? And how would one measure mass versus weight?
I'm familiar with the basic definitions of mass and weight. I know weight is a force measured as newtons and that newtons are kilograms times acceleration. I get in concept how the two are different.
What confuses me is, why is weight always represented in kg/pounds, units of mass? Like, when you step on a scale, you are measuring your weight, correct? The scale operates by measuring the downward force you exert on it (or the normal force it exerts on you? I don't remember. The principle of the argument is the same either way), which, by definition, is weight.
Is it simply a question of every scale having a built-in calculator that does the math to convert force applied to mass by dividing by g? So that the readout you get is actually telling you your mass and not your weight? Seems possible for modern scales, but does that mean old, non-digital scales had to be crafted to that specification? And why is this common practice instead of using units of force?
But also, in that case, how do we measure mass to begin with? Because newtons are derived units, and kilograms are base units, my instinct would be that that weight is derived from known mass, but in my above explanation, the reverse is true. Idunno, maybe my instinct is just wrong. Are we dependent on a known force acting upon an object, such as gravity, to be able to measure the mass of an object?