How Does Energy Influence Our Understanding of Inertia?

[Physics101]

When dealing with the concept of Inertia (Newton's First Law of motion), is there an explanation of why this is so or do we accept it for what it is based on observations and experiments? While realizing that asking for more and more underlying reasons can be recursive and has to stop somewhere, I was just wondering if Inertia was to be taken as a given.

 

[Danger]

As far as I know, it's based upon very well established measurements. The underlying reason might be known to the biggies in physics, but I've never seen it explained. Okay, this wasn't really helpful, but at least it's a response.

 

[Physics101]

As far as I know, it's based upon very well established measurements. The underlying reason might be known to the biggies in physics, but I've never seen it explained. Okay, this wasn't really helpful, but at least it's a response.

LOL. At least I got a response to this very mundane question.
Okay. Here's my take on it followed by another related question. If I'm off by a lot, then someone please stop and correct me. If I were to take an educated guess at the reason for Inertia, I suppose it has to do with conservation of Energy (never mind the underlying reason for that for a second). When force is applied to an object (mass) causing it to gain velocity, this Inertia is retained as long as the object doesn't encounter some other external force. I suppose in this sense, it makes perfect sense that an object in motion should stay in motion while at rest, it should stay at rest (speaking relative to any given frame of reference).The above behavior seems rather obvious when viewed against background devoid of everything (traditional view of vaccum), but what if this weren't the case? If Space-Time isn't as simple as "nothing," but rather much more complex (as suggested by modern physics), can Inertia be equally sensible and explainable?Consider this scenerio, and once again, stop me if I'm straying into erroneous region. If Space-Time can be thought of as forever expanding (be it in the form of Field or quantized unit that multiplies endlessly -- perhaps the remnant of the Big Bang...) in an isotropic fashion, isn't Inertia simply built-in to the system/background? The force required to "nudge" an object can be equated to moving that mass through this background activity, after which the mass finds itself in a newly shifted point of reference (equilibrium) which will in turn appear as moving away at constant velocity from the original frame of reference (before the force was applied). I believe what I'm trying to describe is somewhat similar to the concept presented in SED.If my line of thinking so far is not too far off the center, I have few more follow-up questions and thoughts. Any responses and guidances will be appreciated.

 

[Danger]

Overlooking the fact that I've had an awful lot of beer at this point, you seem to present a fascinating question. Unfortunately, you're beyond my field of knowledge. I can't wait to see what Astro, Chronos, Chi Meson and others of their ilk have to contribute here.

 

[Physics101]

Overlooking the fact that I've had an awful lot of beer at this point, you seem to present a fascinating question. Unfortunately, you're beyond my field of knowledge. I can't wait to see what Astro, Chronos, Chi Meson and others of their ilk have to contribute here.

LOL. Lots of beer? Some might argue that I've consumed too much alcohol to even suggest this type of notion. If you think this is fascinating or crazy, then read the following thread I started on the QM board. It sort of is a continuation of this concept, but related more to QM.

https://www.physicsforums.com/showthread.php?t=102640

 

[Sir_Deenicus]

Haha, if I had a conclusive answer to your question then be certain that I would already be preparing my nobel speech for next year.

The nature and origin of inertia is unknown and is a subject to strong debates and arguments among its discussers. Take for example Mach's principle, which (in one of its many forms) states that inertia is a result of a bodies interaction with the rest of the universe; some argue such is incosistent with General Relativity while others point out sensbily that such a conclusion can only be reached if the conceptualization of the principle is [mis]approached in an inconsistent manner.

See D Sciama's http://adsabs.harvard.edu/abs/1953MNRAS.113...34S" by the General relativity master, Hermann Bondi and [Joseph Samuel].

There are even more convtraversial claims which argue that inertia is electromagnetic in origin.

http://arxiv.org/abs/physics/0012025"

http://arxiv.org/abs/gr-qc/0209016"

 

[Physics101]

Thaks, Sir_Deenicus. I'll be sure to catch up on reading the links you provided. To tell you the truth, I wasn't even aware that there was any controversy associated with the origin of inertia.

 

[Danger]

Me neither. I just figured that I didn't know enough about it.
And just so's you know's... that's 8 Keith's (pronounced Keets), a couple of Canuk's, and a Kokanee.

Yes, I know that it's kind of wimpy, but given my weight/height rato, it's enough to get me pissed.

 

[Averagesupernova]

What inertia actually is has perplexed me for a very long time. I keep trying to relate it to rotational inertia. Take for instance a flywheel rotating on a horizontal axis that is spun up to a fairly good speed that easily demonstrates resistance to rotating it 90 degrees from its axis. Just why is this? What causes this resistance? I would say that it is because the mass in the flywheel has to follow a back and forth path while rotating. As the mass travels UP on one side of the wheel while the rotating wheel is turning on a vertical axis it has to travel sideways also (left for instance). But when it travels DOWN the other side of the wheel it has to travel right. So the faster it turns in the vertical axis the more distance it has to cover in a left to right motion in the same amount of time. Obviously this takes more energy which is noticed by the resistance in turning the flywheel in the vertical axis. So how does this relate to plain old inertia? I don't know, you tell me. But I've often wondered if it has to do with the orbiting electrons themselves since more electrons means more mass which means more inertia. So assuming that what I've (very) briefly suggested is true, then the particles/subatomic particles must be somehow tied in with spacetime. Yes, I know I haven't really said anything here, I've just illustrated another path that leads to the same old conclusion that matter seems to have a direct connection with spacetime. May I be so bold as to wonder if I have sparked something in someones mind who is much smarter than me who will take this a step farther?

 

[Danger]

The only thing about that that strikes me as maybe a little 'off' is the contribution of electrons to mass. They barely make themselves noticeable in an atom from that standpoint. It's the protons and neutrons that provide the mass.

 

[vaishakh]

Please guys, correct where my concepts are wrong? Inertia as far as understood by me is due to the mass of an object. It is just a ratio between force and acceleration. If there were no inertia all objects would have moved with equal acceleration when provided with equal forces. Does that sound funny or this? Anyway according to me inertia cannot disallow an object from moving. The definition of inertia as the tendency of an object to remain at its state is just a twist of the statement that a net external force needs to be applied on an object to accelerate it. Anyway whatever may be the inertia of an object and may force be as small as it be, still an object should have some displacement. If no then that is not due to inertia. So that way a question that why does objects have mass or what is mass is more meaningful.

 

[Boffin]

There are different competing explanations for this out there. My own view is largely based on Einstein's original concepts, but not necessarily the modern interpretations of them. Inertia is the resistance of energy wavicles changing in the amount of energy they contain as they travel relative to the space continuum. Some people believe that the space continuum is totally empty, but even Einstein believed that the space continuum was a system in which energy moved relative to. When a body changes velocity relative to the space continuum it's energy must change due to the relative change in frequency of the energy, and for this to happen there must be energy supplied. If no energy is supplied then there must of course be a resistance to change in velocity. How the space continuum works is still a great mystery. If it is a granular or grid based system, how does it differentiate between moving in a straight line or arc. Does this make sense?

 

[Danger]

I've never heard that before, Ben. Thanks for the info.

 

[DaTario]

Hi,

I think the author Andre Koch Torres Assis has done an interesting work linking inertia with global gravitational scenario.

I guess this reference (googling his name its enough) will be very interesting to this discussion.

Best Wishes

DaTario

 

[Wishbone]

Can't intertia be defined as an objects tendency for a mass to remain at a certain velocity unless force is acted upon it? Couldn't you say that it is due to the fact that the equation for acceleration does not take into account the time that the partcile has been moving at a certain speed? i.e. it doesn't matter how long something has been moving, it needs a force to accelerate?

 

[Physics101]

Can't intertia be defined as an objects tendency for a mass to remain at a certain velocity unless force is acted upon it? Couldn't you say that it is due to the fact that the equation for acceleration does not take into account the time that the partcile has been moving at a certain speed? i.e. it doesn't matter how long something has been moving, it needs a force to accelerate?

Well, that is more or less how inertia behaves, but I was asking a more fundamental question of why it behaves that way. For example, we know that light bends under the influence of gravity (takes geodesic path), so we can explain such behavior. Now, inertia dictates that an object in motion tends to stay in motion and object at rest tends to stay at rest (all relatively speaking, of course). Why the heck is that? Is it some force (dark energy?) or some space-time curvature that causes this? I would tend to go with some form of isotropic dark energy as the underlying cause, but this is pure speculation (and we know how dangerous that can be on these boards).

 

[Wishbone]

Well I think when you ask why at that fundamental of a level, you are really getting into more of philisophical or religious questions, something that is out of the boundraies of physics. I always looked at physics as descripitions of events, unable of answering the question why at that fundamental of a level

 

[Astronuc]

http://www.padrak.com/ine/INERTIA.html
Interesting comment about Ernst Mach.

http://en.wikipedia.org/wiki/Inertia
Nice summary of the matter. [pun unintended]

Inertia is "a body's resistance to change" in motion. Mass is a measure of inertia, by vitue of \vec{F} = m\vec{a} = \dot{\vec{p}}, where \vec{a} is acceleration, and \vec{p} is momenum (\vec{p} = m\vec{v}), or m = |\vec{F}|/|\vec{a}|.

Weight and Mass
http://theory.uwinnipeg.ca/mod_tech/node25.html

Presumably GR and String Theory would attempt to explain Interia, but I am not familiar with any theories.

I tend to agree with Wishbone, that the understanding of some things is possibly beyond science. The question "What is charge?", would also be as difficult to answer as "What is Inertia?", or more generally, "Why does charge/inertia behave the way it does?"

Physics (from the Greek, φυσικός (physikos), "natural", and φύσις (physis), "nature") is the science of the natural world dealing with the fundamental constituents of the universe, the forces they exert on one another, and the results produced by these forces.

http://en.wikipedia.org/wiki/Physics - a nice discussion of physics.

We tend to define things in terms of change or how things influence/interact with one another, and most of the time that is sufficient, i.e. for the most part, it is more important to know how things work than why, but sometimes it is important to know why.

 

[X-43D]

No one knows. I think it has to do with the properties of the vacuum.

 

[vaishakh]

Well, that is more or less how inertia behaves, but I was asking a more fundamental question of why it behaves that way. For example, we know that light bends under the influence of gravity (takes geodesic path), so we can explain such behavior. Now, inertia dictates that an object in motion tends to stay in motion and object at rest tends to stay at rest (all relatively speaking, of course). Why the heck is that? Is it some force (dark energy?) or some space-time curvature that causes this? I would tend to go with some form of isotropic dark energy as the underlying cause, but this is pure speculation (and we know how dangerous that can be on these boards).

Inertia is due to a body having mass. That is the physical reason behind a body's tendency to remain at its mechanical state.

 

[Dmstifik8ion]

Doesn’t inertia speak for itself? An object which is no longer influenced by a cause will no longer be effected to change; its identity is established. Cause and effect imply interaction between two or more objects, an exchange of energy or mass.

I don’t suppose it would suffice to ask, “Why should/would an object exhibit any change in its properties or characteristics when not being effected by another (causal) object?”

A perspective for those under the influence: Once the universe has taken to spinning around and/or moving relative to an object this establishes the nature of the object the universe and their relationship as well. We no longer need to consider which caused and which was effected.

 

[Yor_on]

Reading Astronuc.
" We tend to define things in terms of change or how things influence/interact with one another, and most of the time that is sufficient, i.e. for the most part, it is more important to know how things work than why, but sometimes it is important to know why."


I know that this is an old question:) in many ways.
But the main attraction to me with physics is not to be able to describe 'forces' mathematically.
Rather it is to try to understand the reasons why 'forces' do as they do.
That to me is physics.

The first description is more about those tools handmade by us to manipulate those same 'forces'.
The mathematical tools will change with our understanding but the underlaying questions remain.
Or do you disagree?

 

[russ_watters]

Disagree. What you describe is philosophy, not physics.

 

[||spoon||]

When some of you say you believe such questions as this (fundamental questions about WHY things are as they are) are beyond the realm of science, it made me wonder: Would a grand unified theory be expected to explain such fundamental questions about nature?

On a side note; if a grand unified theory does exist, would the theory itself predict the outcome of physicists' quest to discover said theory? I suppose this is a question for the philosophers, but nevertheless quite thought provoking.

 

[Yor_on]

If so, how would you characterize Einstein, or Feynman?
The impression I got from both is that they first had an idea (well, more than one perhaps:)
Then they started to test them.
And after that came the mathematical tools for using, testing and developing those ideas further.

I think?

 

[Tac-Tics]

If so, how would you characterize Einstein, or Feynman?
The impression I got from both is that they first had an idea (well, more than one perhaps:)
Then they started to test them.
And after that came the mathematical tools for using, testing and developing those ideas further.

I think?

There are countless terrible, awful, worthless theories. People have thought all sorts of crazy, stupid things in the history of physics and science in general. (Actually, they still do). People thought the Earth was the center of what we would consider now a teeny-tiny universe. People thought heat was a liquid. That electricity was a kind of fire. That light would travel at speeds dependent on the observer. That matter was made of indivisible balls that stuck together. All sorts of crazy stuff.

You don't just come up with a theory out of nowhere. The best method we have is to refine existing theories. To take a model which almost works and tweak it until it does work. Even with Einstein, his idea that time is relative didn't spring from a vacuum. He lived in a time when intelligent people began to question Newton's assumptions about the nature of time. Feynman built his gem QED by smelting three decades worth of quantum theory and broken glass.

The exact mathematical statement doesn't come until later, but the reasoning up to the creation of a good theory is always going to be heavily rooted in intuition which follows the known mathematical laws of the universe.

 

[Yor_on]

Einsteins world had very little to do with the one preceding it, to my eyes.
I agree on that the 'ground' existed, but the way(s) he 'twisted' spacetime together was new.
And still are:)

You're quite right in saying that a new theory will have to be grounded somewhere though.
As for the best method would be to 'tweak' existing theories into better compliancy?
Depends on how big the discrepancies are I would say.

" Renormalization was first developed in quantum electrodynamics (QED) to make sense of infinite integrals in perturbation theory. Initially viewed as a suspect, provisional procedure by some of its originators, renormalization eventually was embraced as an important and self-consistent tool in several fields of physics and mathematics. "

:)

 

[D H]

Einsteins world had very little to do with the one preceding it, to my eyes.

It certainly did. Special relativity falls out from two simply stated hypotheses: the laws of physics are the same in all inertial frames and that the speed of light is the same to all inertial observers. The first hypothesis, the principle of relativity, goes back to Galileo. The second hypothesis, the invariance of the speed of light, was exactly what Maxwell's equations predicted and was well-confirmed by the Michelson-Morley experiments. While Einstein may or may not have been familiar with the Michelson-Morley experiments, he most certainly was familiar the Maxwell's equations.

The Nobel committee did not mention Einstein's work on special relativity in part because there were several people who contributed to the theory, primarily Lorentz and Poincaré. Lorentz and Poincaré came up with a theory before Einstein whose results are mathematically indistinguishable from Einstein's special relativity. Einstein's genius was in identifying his two simple hypotheses as the basis for his theory. The theory developed by Lorentz and Poincaré was very ad-hoc in comparison to special relativity.

General relativity builds on top of special relativity. Einstein needed help from many other physicists and mathematicians to finally arrive at general relativity eleven years later.

 

[Fra]

But the main attraction to me with physics is not to be able to describe 'forces' mathematically.
Rather it is to try to understand the reasons why 'forces' do as they do.
That to me is physics.

I doubt these question belongs to "classical physics" but I think the ultimate question here is the distinction between what one can call "the body of established scientific theories" as in the strongly and well corroborated theories, and the growth/creation/expansion of science (ie. the scientific METHOD).

If we take Poppers view of the scientific metod, the question is, if the scientific process itself can be described in a scientific way? Or is the "notion of scientific method" itself somehow philosophy?

In his desired to bring deduction into the scientific method, popper IMHO fails to acknowledge the importance of the hypothesis generation (which is clearly important for the GROWTH of new science), popper dismisses this important question to at best the "psychology of the scientists".

I can help holding the opinion that someone that wants to understand how nature works, can not accept such easy escape.

When we are talking about the expansion of science, or the "scientific method", rather than just the body of "established scientific theories" things do get philosophical. Now if one accepts that as an excuse for thinking it's not relevant to the progress of physics is a matter of opinion I think. I think it's important.

I also think that the "logic" of using/exploiting currently established theories, is totally different than the "logic of discovering" new theories. In the latter case it seems difficuly to be categorical on what's relevant or not.

/Fredirk

 

[Yor_on]

DH, Thanks for your thoughtful reply here.
Although I agree that Einstein built on others he didn't do it without choosing.
If you have an idea that you want to prove to others, you will look for already existing evidence for it.
That's how I see Einstein 'building' on others, not unlike most of us:) when/if we believe we got something interesting/new.
As an example I would like to point out that even when he a good idea of how acceleration equalized gravity he still didn't have the math for describing it.
This I hope explains how I see Lorentz and Poincaré work, as relating to Einstein.
First you need to 'invent' SpaceTime, then see the implications, and search/find the appropriate math for describing it.
That as you naturally will use/look for the best tools you can find, to define your thoughts that others might accept them.

I'm not saying that he was 'alone' either.
But he developed a very new 'vision' of Space and Time, and thereafter kept building mathematical and experimental evidence for it.
Not 'alone' any more, but that first 'vision' of his, that was his own.
And that is to me 'pure physics'.
Somewhat like 'magic':)

---------------
Fra we seem to be thinking along similar lines here.

Popper is interesting.
He says that you should make your most daring theory and then test it for fallibility.
If it fails in any way it would be proved false, As when a hypothesis fails to describe reality.
(although he changed/loosened up that view later if I got it right?)

Also he found no proofs to be without reasonable doubts.
His view (as I understand it) was that there was no 'archetypal' truths at all.
Although falsifications there existed in abundance :)

In a way he is similar to George Berkeley.
Berkeley said " To be is to be perceived "
Both refused to believe in any ultimate truth.
For myself I find Berkeley to be nearer my view of the world than Popper though.
That as it's the observer that is the final arbiter of 'reality'.

So where Popper is trying to create a phenomenological world 'outside' ourselves when 'spliting' our experience of the world in those three parts.
The 'material' world, (stars, Earth etc), the world of our 'experiences' and the world of 'produce' from our thoughts and endeavors.
Berkeley instead goes to the 'center' of all phenomenology, namely consciousness itself.
Which after all is the very thing making any 'sense' out of SpaceTime:)

"There was a young man who said, "God
Must think it exceedingly odd
If he finds that this tree
Continues to be
When there´s no one about in the Quad."


Dear Sir,
Your astonishment´s odd
I am always about in the Quad.
And that´s why the tree
Will continue to be,
Since observed by
Yours faithfully,
God"

And yes, Berkeley was a priest.
But then again, there are Gods and there are Gods:

(Sorry but I just had to rewrite this..
The 'flow' of it was terrible.)