This one's been on my mind for a while: how does one define mass mathematically?
I know balances measure strain using a strain gauge, but strain relates to weight (force) not mass. Does that make mass a function of weight and altitude? That's pretty counter-intuitive (it'd be nicer to say weight were a function of mass and altitude).
Maybe I've overlooked one definition of mass, but all the ones I can think of stem from force or velocity. That includes molar mass, because molar mess stems from the mole concept, which stems from measurements of Avogadro's number. The only determination of Avogadro's number I know of is Perrin's, and that one depends on velocity squared.
Maybe specific heat? q = C m dT