Clarification on Gravity

Quote from: cbarnett97 on February 11, 2009, 07:51:20 PM

Quote from: TheEngineer on February 11, 2009, 03:13:56 PM

Quote from: cbarnett97 on February 11, 2009, 12:19:45 PM

A pound is a unit of weight now?

It has been for some time now...

So if you write a report you write that you started with 2 kilograms which weghed 19.6 kilograms? 

It would be nice if you could keep your units straight.  Maybe that is why all your arguments suck so badly...

I am not the one arguing that it is fine to use kilograms as a unit of force and as a unit of mass

Neither am I.   

The  optical Aharonov-Bohm cannot be explained by gravity as a fictitious force? I'm not disagreeing with you I'm just not sure how. Is this because light in moving media is analogous to light traveling in a curved spacetime?

I don't think you have actually read the first post.  You keep saying the same things over and over.  There is a difference between gravity and gravitation.

For a start every textbook I have read including my first year textbook (Young & Freedman) calls it Newtons Universal Law of Gravitation. A quick check on t'internet seems seems to show this as well. So I'm not sure that I agree with the statement that only gravity comes from Newton. This means that I also disagree with;
"Gravity is a pseudo force that only arises by taking a non inertial frame of reference to be inertial.  Gravitation is a consequence of the deformation of space, no force between objects necessary."

The Internet links in that post seem to pick one word and stick with it (what I normally do). I forget what my old GR textbook does, I seem to remember that its pretty liberal with its usage of both not that I was paying that much attention. The rule of thumb I use is gravity is the force that keeps us on the ground and gravitation is the general attraction between two massive bodies, obviously extended to anything with energy in GR. The most rigorous formal definition that I know of in relationship to the Earth is from an old mechanics textbook (Goldstein if memory serves). Where the Earths gravity field is defined as the sum of its gravitational field and its centripetal acceleration and its gravitational field is the field due to its mass distribution. This is the one I would use in an exam.

edit: note to self - read; then click post.

The  optical Aharonov-Bohm cannot be explained by gravity as a fictitious force? I'm not disagreeing with you I'm just not sure how. Is this because light in moving media is analogous to light traveling in a curved spacetime?

It's possible I was referring to a specific example I had in mind with respect to frame dragging, so in some cases perhaps it can be.  I'd have to think a bit more about it before I could answer that one for definite. Light travelling through a medium can be compared, in some respects, to light travelling through curved spacetime, although one must be careful to avoid making the link too all-encompassing since curved spacetime has some unique effets which even variable refractive index media do not share.

The possible experimental angles into quantum gravity are something I feel I should no more about. Though its a bit far more my normal track to justify learning about in work time. I am trying to understand looking at high energy cosmic neutrinos as a source of lorentz invariance violation. I was just wondering if you knew of some good material.

This means that I also disagree with;
"Gravity is a pseudo force that only arises by taking a non inertial frame of reference to be inertial.  Gravitation is a consequence of the deformation of space, no force between objects necessary."

What about it is too much for you?

For a start every textbook I have read including my first year textbook (Young & Freedman) calls it Newtons Universal Law of Gravitation.

You might as well chuck that book into the trash.

So I'm not sure that I agree with the statement that only gravity comes from Newton. This means that I also disagree with;
"Gravity is a pseudo force that only arises by taking a non inertial frame of reference to be inertial.  Gravitation is a consequence of the deformation of space, no force between objects necessary."

Why are you disagreeing with that?

The rule of thumb I use is gravity is the force that keeps us on the ground

Only when we assume we are at rest. In fact, we are not at rest.

Neither am I.   

So only a pound is a force not a mole?

A mole is not a force, no.   

A mole is not a force, no.   

I meant to say slug.

Quote from: TheEngineer on February 12, 2009, 04:56:40 PM

A mole is not a force, no.   

I meant to say slug.

A slug is not a force, no.   

Quote from: cbarnett97 on February 12, 2009, 05:03:55 PM

Quote from: TheEngineer on February 12, 2009, 04:56:40 PM

A mole is not a force, no.   

I meant to say slug.

A slug is not a force, no.   

So lbft/s² is not a force?

Quote from: TheEngineer on February 12, 2009, 05:31:04 PM

Quote from: cbarnett97 on February 12, 2009, 05:03:55 PM

Quote from: TheEngineer on February 12, 2009, 04:56:40 PM

A mole is not a force, no.   

I meant to say slug.

A slug is not a force, no.   

So lbft/s² is not a force?

No, it is not.

Quote from: cbarnett97 on February 12, 2009, 05:35:11 PM

Quote from: TheEngineer on February 12, 2009, 05:31:04 PM

Quote from: cbarnett97 on February 12, 2009, 05:03:55 PM

Quote from: TheEngineer on February 12, 2009, 04:56:40 PM

A mole is not a force, no.   

I meant to say slug.

A slug is not a force, no.   

So lbft/s² is not a force?

No, it is not.

Uh yeah it is, just not in SI units

An lb is a unit of force, not mass.  Therefore, your definition of a slug is not correct.

The proper definition of a slug is

1 slug = 1 lb s^2/ft

and it is a unit of mass.  Please, for your own sake, look it up.

Lol.

In defense of my and many other 1st year texts the following book also refer either to Newtons Universal Law of Gravitation or Newtonian Gravitation.

Gravitation and Spacetime (Moller)
300 Years of Gravitation (Hawking and Istral)
Relativity and Gravitation (Tourrenc)

The very complete book, Gravitation by Misner, Thorne and Wheeler doesnt really go into the definitions but infers that gravitation is the mutual attraction of two massive bodies and refers to a curved space time as what me mean today by gravitation. Though refers to Newtonian and Einstein's gravity. I'd be lying if I said I cared but I sticking the the one from Goldstein's classical mechanics.

The very complete book, Gravitation by Misner, Thorne and Wheeler doesnt really go into the definitions but infers that gravitation is the mutual attraction of two massive bodies

Then they are wrong.

and refers to a curved space time as what me mean today by gravitation.

Right.  So where is all of your confusion coming from?

Because the way you word it it sounds like the word gravitation comes only from that interpretation. Myself, wikipedia (eugh, but its easily checkable) and every book I can find that says it explicitly refers to Newton's Universal Law of Gravitation. It was only when I came to the forum that I heard gravitation defined as anything of than the mutual attraction between two bodes. I have no dispute that the current interpretation of that is a curved space time. It was before that explained by Newtons laws albeit without a mechanism. I'd much rather discuss how we will be interpreting it in 100 years time rather than how we did 100 years ago. Without meaning any offense I'm going to take my definitions from what I think the best book on classical mechanics every not a forum trying to show the world is flat.

Mate, it's really not worth it - just accept the definitions of this forum and work within that framework.  In the main the words are interchangable, but here where there has been intense debate over the differences between Newtonian and Einsteinian gravitation, this consensus has emerged... best just to roll with it.

Also, an excellent point to start in your studies of potential Lorentz Invariance-violating experiments is the work of Matthew Mewes and Alan Kostelecky on the 'Standard Model Extension' (SME).  They have also released a paper that summarises all the various experiments and the experimental limits they have established, but to understand that you would need to read their original papers. Try this link to the arXiv:

http://arxiv.org/PS_cache/arxiv/pdf/0801/0801.0287v2.pdf   (their latest update on experimental constraints in all sectors of the theory)

http://arxiv.org/find/all/1/au:+kostelecky/0/1/0/all/0/1   (link to the search results for all the papers you should need)

I stress that these guys are serious theorists and have built up what is now the accepted framework for testing for Lorentz Invariance violations.  Have a hunt around the results and try not to lose heart if you run into maths you don't understand - it took me a whole PhD to get my head around the most basic bits!!

Yeah im not so sure why im getting wound up by this, its not like I dont know how things work around here.

Thanks for those links anyway ill take a look.

Yeah im not so sure why im getting wound up by this, its not like I dont know how things work around here.

Thanks for those links anyway ill take a look.

Eh, yeah, Engy just likes to do this so he can take pleasure in pwning noobs.  It's a little funny that he just called one of the most authoritative books on general relativity (Gravitation by Misner, Thorne and Wheeler) wrong.

It's a little funny that he just called one of the most authoritative books on general relativity (Gravitation by Misner, Thorne and Wheeler) semantically wrong in the context of this forum.

Fixed.   

Why are the definitions of gravity and gravitation different on this website? Presumably the definitions changing is just going confuse people who know what they are and make learning harder for those who don't as it will not make sense if they try to read physics text books.

Because in most textbooks, the main goal is ease of understanding. The kind of nuances discussed here are not considered relevant in globularist physics. For that reason, they do not force their readers to learn about distinctions they will never need to discuss (unless of course they stumble upon fes.org).

Why are the definitions of gravity and gravitation different on this website? Presumably the definitions changing is just going confuse people who know what they are and make learning harder for those who don't as it will not make sense if they try to read physics text books.

Because they like to be pedantic jerks and harass the noobs (not that most of the noobs don't deserve it). 

The main thrust of this forum is at times unclear to me but seems to revolve around gravity being Newtons theory and gravitation being Einsteins theory. This is just plain wrong and I don't understand how it helps the debate here either. To me definitions the rest of the world uses are actually more useful here. As I understand it Fe theory explains gravity as the Earth being in a frame accelerating at g. I have no problem with this, in any theory we could be in an accelerating frame, or the rest of the universe accelerating in the other direction or something. Still though the contribution of the Earths mass distribution needs to be discussed. I don't understand how any of this is helped by using a set of custom and physically not very useful definitions.

Its not pedantic, its just different. Its not the physics version of going through checking everyones grammar its randomly redefining what a verb and what a noun is.

Quote from: bowler on February 16, 2009, 02:26:12 PM

Why are the definitions of gravity and gravitation different on this website? Presumably the definitions changing is just going confuse people who know what they are and make learning harder for those who don't as it will not make sense if they try to read physics text books.

Because they like to be pedantic jerks and harass the noobs (not that most of the noobs don't deserve it).