# How is gravity manifested?

The explanation of the interrelation between mass and gravity is not any more helpful than explaining magnetism as molecules lining-up in a mass or like-charges repel and unlike-charges attract.
Everything I read is like that! It does not explain the mechanisms; but how they work.
It is like asking someone what is time. They start explaining how a time-piece works: not what time is.
E.g. What is a charge on an electron or a proton? The mention of quarks or strings do not do it. Their presence may be the cause; but how do they cause it?
With regards to gravity --- how is the effect of gravity caused by the presence of mass?

 zanderbaxa Posts: 62, Reputation: 10 Junior Member #11 Nov 7, 2011, 02:55 AM
http://nykkyo.byethost5.com/doppler.pdf
 ebaines Posts: 10,138, Reputation: 5589 Expert #12 Nov 8, 2011, 09:47 AM
Quote:
 Originally Posted by zanderbaxa http://nykkyo.byethost5.com/doppler.pdf
 zanderbaxa Posts: 62, Reputation: 10 Junior Member #13 Nov 8, 2011, 05:24 PM
I tried attaching it here
Attached Images
 doppler.pdf (49.0 KB, 69 views)
 ebaines Posts: 10,138, Reputation: 5589 Expert #14 Nov 9, 2011, 06:06 AM
There are at least three significant errors in your attachment. Before getting into the details, note the graph you present is clearly incorrect, which provides a strong clue that there are errors. Note that it predicts that it's impossible to hear an ambulance siren approaching you. You say that the frequency of the sound as the source approaches you goes "beyond the hearing range" as the angle $\theta$ goes to $\pi/2$. Actually the graph says it goes all the way to infinity. And that this happens even if V_s is very small. Consequently - your graph says that it's impossible to hear a car passing you at, say, 30 MPH. Obviously this is not correct.

So given the clearly incorrect results let's see where the errors in your math are. There are three that I see:

1. The relative velocity of the the source as seen by the observer is $V_o = V_s \cos \theta$, not $
V_s \sec \theta$
. Your formula goes to infinity at $\theta = \pi/2$ when clearly it should go to zero (as a source passes you for a brief instant it is neither approaching nor receeding - so it's relative velocity is 0). hence it's clear that the secant term is incorrect.

2. The velocity of the wave front is set by the properties of the medium (air, in the case of sound), NOT by the speed of the source. So your equation $f_o = (V_s/\lambda) sec \theta$ is not right on two counts - first because the secant tem is incorrect and second because of your incorrect assumption that the velocity of the wave front is dependent on the velocity of the source.

3. Third error is in coming up with the function $\sec(x) + \tan(x)\sec(x)$ You don't indicate why you think it appropriate to add together what you claim are the relative velocity and relative frequency.

Back in post #6 of this thread I had directed you to a web site that demonstrates the Doppler effect pretty clearly - did you look at at that, and if so do you have any questions about it? I had also posted a formula in post #8 for frequency as measured by the observer as determined by the source frequency and relative velocity - again, have you read it?
 zanderbaxa Posts: 62, Reputation: 10 Junior Member #15 Nov 9, 2011, 09:34 PM
f+dela-x is appropriate. The derivative of f (delta-x) is sec(x)tan\n(x)! Are you implying f=1/T
(by definition) is wrong? Because f tends to infinity as T goes to zero? Or black holes do not exist
because their mass is infinite and matter entering its horizon does not disappear? Or singularities are fictitious (in complex variable theory, in wave filters) because at that poinbt f is 1/0?
 ebaines Posts: 10,138, Reputation: 5589 Expert #16 Nov 10, 2011, 06:57 AM
You are confusing so many things that it's going to be difficult to untangle.

1. Your sec(x) function is wrong, as shown earlier. Yes, the derivative of sex(x) is sec(x)tan(x), but that simply shows that you know how to take the derivative of the wrong function.

2. Yes f=1/T, where T is defined as the period of the wave. But no, f does not go to infinity, because T does not go to zero unless the source velocity is equal to the speed of sound. When a jet airplane travels at the speed of sound in essence all the sound waves pile on top of each other creating a discontinuity that we perceive as the sonic boom. But your PDF document claims that sounds from all objects create sonic booms independent of how fast they are traveling. Don't you see that that's just plain wrong?

3. Your past few posts have been all about Doppler effects for non-relativistic conditions, such as sound waves in air. Please do not start throwing in issues about black holes as that just confuses things. Let's get the Doppler effect understood for the simple case of sound waves in air before worrying about how gravity can affect light waves. But ... no, the mass of a black hole is not infinite.

You have not as yet responded as to whether you agree or not with posts #6 or #8.
 zanderbaxa Posts: 62, Reputation: 10 Junior Member #17 Nov 11, 2011, 08:26 PM
I am not just throwing black holes ... Red-Shift is touted as similar to Doppler shift, is that also confusing?
 zanderbaxa Posts: 62, Reputation: 10 Junior Member #18 Apr 4, 2012, 05:42 PM
I think I figured it out. Matter displaces an elastic medium (like quantum foam) and the restoring force (trying to compressing the matter) is gravity (like a rock submerged in water).
 sean_s Posts: 103, Reputation: 1 Junior Member #19 Apr 9, 2012, 01:49 PM
the task of science is to describe the WHAT question, not HOW question. Hence,science can only answer what happenes when there is gravity (they follow the rule of gravity)

Science attempts to answer a modifyied HOW question, as in "WHAT makes gravity", which is a modified version of "HOW is gravity made", but it won't really work out.

In the last century, i read in the book, title translates to "consequence of critical scientific theory" that the what question was "made cheaper" by high thinking school of scientists, who attempted to hit the "how" question. Indeed they were of extraordinary genius, but then, science left it's own definition and got merged with philosophy.

I myself have an undergraduate degree in astrophysics, and geology (dual program), so i guess i am lucky enough to compare the science that engages with "how" question (cosmology, sr, gr ) and the "what" question (what animal is that fossil)...

I think we need some radical exploratory discovery, to handle the manifestation question.

I know this question does not answer "how gravity is manifested", but it would be nice to have a more well formed question.

Assuming you wanted to ask "What happens when a mass is placed": The answer is, spacetime bends. The mass changes the geodesics (geodesics are the lines a non-accelerating particle would follow, a generalization of straight line, geodesic to relativity, as straightlines to first law) to a curved shape. All particles now must follow the curved geodesic. A particle that followes a curved path near a massive object, is accelerating according to 1st law, which you see as the "action of gravity"

This explaination indeed consists of holes, which are not quite unambiguously solved.
 zanderbaxa Posts: 62, Reputation: 10 Junior Member #20 Apr 9, 2012, 04:55 PM
Geodesics do follow contours but the contours of space are strains on space as a result of mass displacing it. The bigger the mass the farther reaching the deformation: thus, masses far apart interact. For the most part quantum theory explains subatomic interactions; but when it goes meta-physical (e.g., Schrodinger's cat, entanglement and conscientiousness influencing measurements) it is going off track,

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