# The Naked Scientists Forum

### Author Topic: Are gravity and inertia closely related?  (Read 5672 times)

#### Gary L Kettlewood Jr

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##### Are gravity and inertia closely related?
« on: 26/03/2011 22:30:03 »
Gary L Kettlewood Jr  asked the Naked Scientists:

Hello from Middletown, Delaware  USA,

First, let me express how much I love your podcasts. I am constantly thirsting for knowledge, and your show fits the bill for quenching that thirst.

Now for the question:

When I think of electromagnetism, or time/space, I always get stuck thinking of gravity and inertia.  I somehow feel that they are linked.  I know of no proper theories along these lines, but something feels right in my gut about a special relationship between them.  I have no math or research to back it up, it's just an idea that I have had for quite a while.

Has this idea come up in Physics before that you know of, or am I just off my rocker?  And if there is such speculation already, what impact if any, would it have on helping gravity fit into a unified theory?

Thank you for so much information so entertainingly put forth.

Gary Kettlewood.

What do you think?
« Last Edit: 26/03/2011 22:30:03 by _system »

#### yor_on

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##### Are gravity and inertia closely related?
« Reply #1 on: 26/03/2011 23:03:56 »
Then we are two that thinks so :)
To me inertia is the proof of gravity being 'everywhere'.

It's quite simple, any inertia is a 'gravity' even if 'instantaneous'. An acceleration is, as Jaztra would say, constant 'jerks', also able to be defined as inertial 'reactions' on your accelerations 'action'. which should make even a Geezer to nod agreeably :)
« Last Edit: 26/03/2011 23:22:55 by yor_on »

#### JMLCarter

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##### Are gravity and inertia closely related?
« Reply #2 on: 26/03/2011 23:55:48 »
Both gravity and any other force can cause one frame of reference to accelerate relative to another.
It is one of the founding principals of relativity that an observer inside the accelerating frame cannot distinguish acceleration due to one force from another.

I think there is no doubt that this means that at least in that way gravity is like other forces. There is no "inertial acceleration" in the absence of on force or another.

#### yor_on

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##### Are gravity and inertia closely related?
« Reply #3 on: 27/03/2011 00:21:15 »
If you by that mean that acceleration and gravity is the same?
Yes, I agree.

If you mean that it is the same as Electromagnetism?
No, I do not agree.

#### JMLCarter

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##### Are gravity and inertia closely related?
« Reply #4 on: 27/03/2011 02:33:08 »
Well except that gravity is a force, and acceleration is not; so they don't have the same units. That's a bit pedantic, perhaps, if we are trying to develop an intuitive feel for what the way things work.

What I am saying is that it is the acceleration that impacts observations in/from the frame of reference and NOT the force that causes is, which might be gravity, electromagnetism, weak/strong nuclear etc.

Acceleration can be cause by electromagnetism as much as it can by gravity. Probably we agree.

#### Phractality

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##### Are gravity and inertia closely related?
« Reply #5 on: 27/03/2011 07:57:03 »
Gravity and inertia are two properties of mass. In all known situations, gravitational mass is directly proportional to inertial mass. So yes; they are closely related.

Departing from the mainstream, I believe there is an ether which is incredibly dense in terms of inertial mass; but it has zero gravitation mass. Other than that, I know of no situation where the two properties of mass are not directly proportional to one another.

#### Geezer

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##### Are gravity and inertia closely related?
« Reply #6 on: 27/03/2011 09:05:18 »

Well except that gravity is a force, and acceleration is not; so they don't have the same units. That's a bit pedantic,

It's not pedantic. Force and acceleration are entirely different things. They were both defined long before the concept of Relativity. If the proponents of Relativity wish to define similar concepts, they should define their own terms rather than hijacking terms from another theory.

(I'm anticipating some hate-mail now.)

#### yor_on

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##### Are gravity and inertia closely related?
« Reply #7 on: 27/03/2011 09:44:20 »
JML "What I am saying is that it is the acceleration that impacts observations in/from the frame of reference and NOT the force that causes is, which might be gravity, electromagnetism, weak/strong nuclear etc."

You are thinking of a gravitational acceleration there, right?
As seen from earth watching that apple fall.

To me the apple is in a 'free fall' or better expressed, following a geodesic. That a planet is in 'its way' doesn't matter for that definition. It's about the equivalence of all uniformly moving, or in this case possibly formulated as 'uniformly accelerating' as seen from Earth, frames of reference. A real 'accelerating frame' will have a 'gravity' created as its expression.

If you're inside a dark room, ignoring tidal effects, there will be no difference between that room free falling in the sky above Earth, or 'free falling' in a geodesic in space. You will be weight less in both cases, and all experiments you can do inside it will give the same results, in both cases, as far as I know?

If you can prove it otherwise I'll be interested.
Not using tidal forces, Coriolis etc.
==

Reading this, what one has to consider to accept it is that all uniform motions are the same, no matter their relative speed. It doesn't matter what reference frame you use for defining that speed. Close yourself into that dark room and do your experiments. Ignoring tidal forces there will be no way I know of separating any uniform frame from another, no matter their 'speed', including the apples free fall. What that states is the strongest type of equivalence I know of, that and the way a real accelerating frame always will create a 'gravity' as observed inside that frame, and in the case of a constantly accelerating, at one G, indivisible from Earths own 'gravity'.

And if that is true, a gravitational 'acceleration' is no different. It's still a uniform motion, even though a special case of it. The special case here is called matter, who has some real weird properties, amongst them the ability to 'punch holes' in space :) aka 'warping/distorting' it.
« Last Edit: 27/03/2011 10:05:44 by yor_on »

#### yor_on

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##### Are gravity and inertia closely related?
« Reply #8 on: 27/03/2011 10:27:26 »
That warping matter offers can be seen two ways, as far as I'm concerned (for the moment) that is :) You can see it as a direct effect of matter existing. Something intrinsic to 'invariant mass', stretching space, sort off. Or you just might consider what it would be like if 'gravity' was existent everywhere, but more or less 'neutralized' by SpaceTime? Except in two cases, in the vicinity of 'invariant mass' and possibly also in the vicinity of pure 'energy'. A black hole is defined as being 'energy' at its center, which makes a awful lot of sense, :) if you consider what happens to 'matter' before it ever can become a 'black hole' breaking down all bondings a particle can have.

So what would that make those singularities if that was correct? And what would it make matters affinity for 'gravitational acceleration'? And at what possible 'speed' will we find that same matter before the 'Black Hole' breaks its 'bondings' down?

Pure speculation this :)

#### Phractality

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##### Are gravity and inertia closely related?
« Reply #9 on: 28/03/2011 00:44:31 »
Well except that gravity is a force, and acceleration is not; so they don't have the same units. ...

Einstein's though experiments with elevators demonstrate that gravitational attraction to a large mass, like a planet, is indistinguishable from uniform linear acceleration of the reference frame. Force is mass times acceleration, which is the same as mass times gravity. It's called the equivalence principle.

#### JMLCarter

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##### Are gravity and inertia closely related?
« Reply #10 on: 29/03/2011 01:03:19 »
Phac: "is the same as mass times gravity"

you mean "is the same as mass * acceleration due to gravity". g is acceleration in F=GMm/r². a=F/m. g=GM/r².
this is pretty basic stuff... must be a misunderstanding.

I found a typo in my earlier post
"What I am saying is that it is the acceleration that impacts observations in/from the frame of reference and NOT the force that causes is"
should be
"What I am saying is that it is the acceleration that impacts observations in/from the frame of reference and NOT the force that causes it [the acceleration]"

I don't think I'm breaking the equivalence principle, (whatever form it is quoted in).

« Last Edit: 29/03/2011 01:34:51 by JMLCarter »

#### The Naked Scientists Forum

##### Are gravity and inertia closely related?
« Reply #10 on: 29/03/2011 01:03:19 »