4 ms·
They roughly infer their mass (in kilograms) by assuming 9.8m/s/s gravitational acceleration and using a scale to judge how much mass the resulting 'push' would
by WaxProlix 9y ago
They roughly infer their mass (in kilograms) by assuming 9.8m/s/s gravitational acceleration and using a scale to judge how much mass the resulting 'push' would require given that pull. A scale would tell you that you weight slightly less at the top of a mountain than at sea level, though in reality you'd have the same mass. Same is true on a neutron star.
It's an easy shorthand for the most part, since we're not 'weighing' ourselves in space, on the moon, etc, but in an article about space and physics and whatnot, it can come off as a bit sloppy.
- braythwayt 9y agoEvery single thing about life as we know it, humanity, and our brains is exceedingly sloppy. What makes it work? Error correction! So, thank you.
- thaumasiotes 9y ago> A scale would tell you that you weigh[] slightly less at the top of a mountain than at sea level, though in reality you'd have the same mass. For an illustration of a pedantic distinction, this seems awfully unlikely to be correct. You gain mass by eating and drinking and lose it by urinating, defecating, and breathing; odds are you're not going to have the same mass on the mountaintop.
- StavrosK 9y agoThis is physics, we're clearly assuming a perfectly spherical human with lossless and instantaneous modes of travel.
- WaxProlix 9y ago> pedantic Think you're maybe projecting? It was meant to be a silly example and taking a super uncharitable interpretation (object x at different times or states with different masses) of my statement just to be able to pick a nit strikes me as more pedantic than responding to a request for corrections with my high school level understanding of basic units.
- ricardobeat 9y ago> A scale would tell you that you weight slightly less at the top of a mountain than at sea level, though in reality you'd have the same mass. A pound of force uses 'standard gravity' as a constant, even though it varies across the earth. Sounds just as bad?
- ISL 9y agoA pound of force is defined [1, 2] as 4.448222 N . No gravity necessary (but the IPK is, until the upcoming redefinition of the SI). Yes, that definition was reached using a notion of "standard gravity", but once fixed, it is nothing but a number. [1] https://physics.nist.gov/cuu/pdf/sp811.pdf https://physics.nist.gov/cuu/pdf/sp811.pdf [2] https://en.wikipedia.org/wiki/Pound_(force) https://en.wikipedia.org/wiki/Pound_(force)
- ricardobeat 9y agoStill not any more precise than kg to measure human weight (unless you position the human at the exact right spot on earth).
- ISL 9y agoA properly-calibrated scale/balance will correctly determine the mass of any object in any gravitational field (gravity gradients excepted).
- WaxProlix 9y agoNot just as bad, because you'd be measuring the correct thing, which is force. Not mass. That's all I was getting at - they're different things and depending on context, one can change (weight) where the other does not (mass). That's all.
- ISL 9y ago9.8 m/s^2 need not be assumed. As long as you have a calibration standard, any scale can be calibrated correctly in any gravitational field. If you care about absolute masses at the ~percent scale or better, calibration is requisite.
- smoyer 9y agoBecause a hike like that will really burn off the pounds ... er, I mean kilograms. (Joke)