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How Raganwald Lost His Crown

braythwayt.com

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Re: How Raganwald Lost His Crown

#31

Post by ricardobeat »

WaxProlix wrote: post #18
bryanl wrote: post #15

Earlier quoted context omitted.

Most of the people world weigh themselves in kilograms.

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 'we…

> 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?

Re: How Raganwald Lost His Crown

#32

Post by ISL »

WaxProlix wrote: post #18
bryanl wrote: post #15

Earlier quoted context omitted.

Most of the people world weigh themselves in kilograms.

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 'we…

9.8 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.

Re: How Raganwald Lost His Crown

#33

Post by ISL »

ricardobeat wrote: post #31
WaxProlix wrote: post #18

Earlier quoted context omitted.

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 'we…

> 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?

A 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 [2] https://en.wikipedia.org/wiki/Pound_(force)

Re: How Raganwald Lost His Crown

#34

Post by ricardobeat »

ISL wrote: post #33
ricardobeat wrote: post #31

Earlier quoted context omitted.

> 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?

A 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 [2] https://en.wikipedia.org/wiki/Pound_(force)

Still not any more precise than kg to measure human weight (unless you position the human at the exact right spot on earth).

Re: How Raganwald Lost His Crown

#35

Post by ISL »

ricardobeat wrote: post #34
ISL wrote: post #33

Earlier quoted context omitted.

A 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 [2] https://en.wikipedia.org/wiki/Pound_(force)

Still not any more precise than kg to measure human weight (unless you position the human at the exact right spot on earth).

A properly-calibrated scale/balance will correctly determine the mass of any object in any gravitational field (gravity gradients excepted).

Re: How Raganwald Lost His Crown

#37

Post by gwking »

braythwayt wrote: post #2

Disclosure: A rare self-post. I'd be very grateful for any and all corrections to the story, as I am far from an expert is astrophysics, geology, or pretty-much anything else.

> At some point, a satellite the size of Mars came crashing into the earth, so hard and so fast that about a third of the earth was blasted into space. It didn’t go far–the debris formed a ring around the earth, and gravity eventually compacted it into a single satellite, our moon, but a satellite much larger than our planet’s gravity would normally be able to capture.

Something seems off about "a third": according to https://en.wikipedia.org/wiki/Moon, the Moon's radius is a bit less than a third of Earth's, but its volume is 2% and its mass is just 1%. I'm no expert, but "about a hundredth" seems more accurate.

For what it's worth, I only looked it up because I've come across this discrepancy before, so perhaps I'm missing something!

Re: How Raganwald Lost His Crown

#38

Post by WaxProlix »

ricardobeat wrote: post #31
WaxProlix wrote: post #18

Earlier quoted context omitted.

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 'we…

> 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?

Not 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.

Re: How Raganwald Lost His Crown

#39

Post by braythwayt »

gwking wrote: post #37
braythwayt wrote: post #2

Disclosure: A rare self-post. I'd be very grateful for any and all corrections to the story, as I am far from an expert is astrophysics, geology, or pretty-much anything else.

> At some point, a satellite the size of Mars came crashing into the earth, so hard and so fast that about a third of the earth was blasted into space. It didn’t go far–the debris formed a ring around the earth, and gravity eventually compacted it into a single satellite, our moon, but a satellite much larger than our planet’s gravity would normally be able to capture. Something seems off about "a third": according t…

I could be wrong about this, but note also that not all of the material ejected from the impact wound up in Earth's orbit.

Re: How Raganwald Lost His Crown

#40

Post by crimsonalucard »

> Hark to the lesson of this story: Everything has an explanation.

Great writing. But the lesson is wrong. It has been proven that certain things which are true can never have an explanation: Godels incompleteness theorem.

https://www.wikiwand.com/simple/G%C3%B6del%27s_incompletenes...

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