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What Does Pi Have To Do With Gravity?

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Re: What Does Pi Have To Do With Gravity?

#21

Post by Aardwolf »

Camillo wrote: post #12

This is a terrible article in both content and form. Pretty much the only interesting thing in it is the historical connection between the seconds pendulum and the metre, but then you could just read this instead: http://en.wikipedia.org/wiki/History_of_the_metre

Why is meter spelled "metre" in English? English is a Germanic language, and Germanic languages like Dutch and German happen to have the perfectly reasonable word "meter" for this. But for some reason English chose the romance French spelling "metre", that looks really odd outside of French. Why?

Re: What Does Pi Have To Do With Gravity?

#22

Post by madaxe »

xonea wrote: post #4
PankajGhosh wrote: post #2

Wouldn't this relationship only exist on earth (to be exact on surface of earth)? Unless we redefine 1 meter of length depending on gravitational field on every surface of planet/star...

Yup. So - the answer to the question "What Does Pi Have To Do With Gravity" is pretty much - nothing. The article also notes that it does not work it you use feet instead of meters, hence basically already answering the question.

Pi relates to SI units, but not gravity.

Unless you wanna be esoteric and go herp derp g=(GMm)/((orbital circumference)/2pi)^2 at which point tada QED!

Also tidal forces, lots of pi when your cranking those out. And keplers laws of planetary motion, which last I checked are all about gravity.

Re: What Does Pi Have To Do With Gravity?

#23

Post by madaxe »

Aardwolf wrote: post #21
Camillo wrote: post #12

This is a terrible article in both content and form. Pretty much the only interesting thing in it is the historical connection between the seconds pendulum and the metre, but then you could just read this instead: http://en.wikipedia.org/wiki/History_of_the_metre

Why is meter spelled "metre" in English? English is a Germanic language, and Germanic languages like Dutch and German happen to have the perfectly reasonable word "meter" for this. But for some reason English chose the romance French spelling "metre", that looks really odd outside of French. Why?

We formalised spelling in the 18th c., independently of one another. No particular reason beyond that, afaik.

Re: What Does Pi Have To Do With Gravity?

#24

Post by Retric »

claudius wrote: post #11
andrewflnr wrote: post #5

Earlier quoted context omitted.

No, the answer is that our units were constructed so that pi has something to do with gravity.

If you think of π as the relation between the circumference of a circle and its diameter, then it does have something to do with gravity (and dimensions) - in a one-dimensional world, for example, the force of gravity would not fall of with distance, as it is the gravitational flux that is conserved. If there is only one dimension, there's no way for it to disperse away from a body, hence it is constant. If you then…

That depends on how you pick the gravitational constant. It's trivial to make e show up in gravitational equations but with the right g you can avoid pi in a our world. At which point you can play around with a different number of dimensions, but that's just math and has nothing to do with physics.

Re: What Does Pi Have To Do With Gravity?

#25

Post by opminion »

Aardwolf wrote: post #21
Camillo wrote: post #12

This is a terrible article in both content and form. Pretty much the only interesting thing in it is the historical connection between the seconds pendulum and the metre, but then you could just read this instead: http://en.wikipedia.org/wiki/History_of_the_metre

Why is meter spelled "metre" in English? English is a Germanic language, and Germanic languages like Dutch and German happen to have the perfectly reasonable word "meter" for this. But for some reason English chose the romance French spelling "metre", that looks really odd outside of French. Why?

It's consistent with "centre" vs American "center"

Re: What Does Pi Have To Do With Gravity?

#26

Post by Camillo »

shardling wrote: post #15
Camillo wrote: post #12

This is a terrible article in both content and form. Pretty much the only interesting thing in it is the historical connection between the seconds pendulum and the metre, but then you could just read this instead: http://en.wikipedia.org/wiki/History_of_the_metre

I guess I find that a weird comment -- the entire point of the article was the historical connection, so if that was the only thing that was interesting, how does that make it terrible? It seems like most people on HN were expecting something very different, and so were disappointed when it was "just" a bit of history. As someone with a backbround in physics, but who had never heard this tidbit, I thought it was pret…

Because it was horribly written, even for a random blog post; and because the time spent reading it could have been better spent reading the Wikipedia article, which would have been both more informative and more pleasant.

Basically, the author wrote a rehash that is worse than its source in every possible way. The only reason to do that is when you're forced to do it, as with an essay in school, or, in this author's case, an arbitrary requirement to write something for Pi day. But that's still no reason to post it on HN.

Re: What Does Pi Have To Do With Gravity?

#27

Post by Camillo »

Aardwolf wrote: post #21
Camillo wrote: post #12

This is a terrible article in both content and form. Pretty much the only interesting thing in it is the historical connection between the seconds pendulum and the metre, but then you could just read this instead: http://en.wikipedia.org/wiki/History_of_the_metre

Why is meter spelled "metre" in English? English is a Germanic language, and Germanic languages like Dutch and German happen to have the perfectly reasonable word "meter" for this. But for some reason English chose the romance French spelling "metre", that looks really odd outside of French. Why?

Because the word has its origin in the Greek metron, and has nothing to do with Germanic languages whatsoever.

Besides, there are countless precedents of English words with a mute final "e" and a schwa inserted between two consonants, e.g. "little".

Re: What Does Pi Have To Do With Gravity?

#28

Post by calhoun137 »

This is what i was hoping to read in this article:

If pi is defined as the ratio of the circumference of a circle to its diameter, then a gravitational field indeed changes pi, and by measuring this change, its possible to measure the strength of gravity.

A quick way to understand this is to realize that "straight lines" (geodesics) are defined as the path taken by a beam of light, and gravity causes the path of light to bend. Measuring the difference is the same as measuring the curvature of space time, which when multiplied by a constant IS the strength of the gravitational field according to general relativity.

Another way to see it: take a sphere and draw a circle on it, then measure pi. You can determine the curvature of the sphere once you measure the difference with pi on a flat piece of paper.

Re: What Does Pi Have To Do With Gravity?

#29

Post by shardling »

madaxe wrote: post #19
shardling wrote: post #15

Earlier quoted context omitted.

I guess I find that a weird comment -- the entire point of the article was the historical connection, so if that was the only thing that was interesting, how does that make it terrible? It seems like most people on HN were expecting something very different, and so were disappointed when it was "just" a bit of history. As someone with a backbround in physics, but who had never heard this tidbit, I thought it was pret…

Well, because his conclusion was basically "shit, I don't know, something to do with sine waves and SHM I guess". I'd explain why here but it wouldn't fit in this margin.

Heh, I guess since I already know how that works out, I'm glad it was glossed over.
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