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Author Topic: Are inertial forces real?  (Read 11631 times)

lean bean

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Re: Are inertial forces real?
« Reply #50 on: 02/12/2013 13:25:19 »
tip is at the center of the body and whose tail is the center of the cavity. The force is parallel to and in the direction of this vector.

Be patient here, so, if I have a ring of test particles around the cavity walls would they converge to centre of cavity? What will they do at the centre? I may be getting my tip and tail confused...

Or, other way round. If I have a sphere of test particles centred on the cavity centre, would each particle travel radially outwards to the walls? :)

Thank goodness for the modify button :)




« Last Edit: 02/12/2013 15:50:16 by beany »
 

Offline Pmb

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Re: Are inertial forces real?
« Reply #51 on: 02/12/2013 17:39:53 »
tip is at the center of the body and whose tail is the center of the cavity. The force is parallel to and in the direction of this vector.

Be patient here, so, if I have a ring of test particles around the cavity walls would they converge to centre of cavity? What will they do at the centre? I may be getting my tip and tail confused...

Or, other way round. If I have a sphere of test particles centred on the cavity centre, would each particle travel radially outwards to the walls? :)
Neither. That would imply the presense of tidal force. Remember that the field is uniform which means that no matter where you place a particle in the field the magnitude and direction of the force on the particle will be indepenant of where the particle is. Therefore the field lines are parallel and all point in the same direction. I updated the page with a new diagram to illustrate this fact. See Figure 2 below

http://home.comcast.net/~peter.m.brown/gr/grav_cavity.htm
 

lean bean

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Re: Are inertial forces real?
« Reply #52 on: 02/12/2013 18:56:36 »
Neither. That would imply the presense of tidal force. Remember that the field is uniform which means that no matter where you place a particle in the field the magnitude and direction of the force on the particle will be indepenant of where the particle is. Therefore the field lines are parallel and all point in the same direction. I updated the page with a new diagram to illustrate this fact. See Figure 2 below
http://home.comcast.net/~peter.m.brown/gr/grav_cavity.htm

Yes, I did 'see' the element of tidal accelerations there in my own descriptions and  was confused by that. :)
You must have updated just as I come away from that page, I will have a chew on the new page now. And, yes, I see what you mean now about the placing of tip and tail giving the vector direction, I had the vector joining particle and centre!!
« Last Edit: 03/12/2013 18:36:15 by beany »
 

lean bean

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Re: Are inertial forces real?
« Reply #53 on: 03/12/2013 18:37:02 »
Pete, I have looked at your updated page and have to say it's way above my head.
So, all I can say is, Iím obviously  not qualified to say whether your selection and use of the equations is correct or not, but it would be the cherry on the cake if you could have explained the mechanism by which the force attracts, and not just the behaviour of an assumed force of attraction. :)
 

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Re: Are inertial forces real?
« Reply #54 on: 03/12/2013 23:25:25 »
Pete, I have looked at your updated page and have to say it's way above my head.
So, all I can say is, Iím obviously  not qualified to say whether your selection and use of the equations is correct or not, but it would be the cherry on the cake if you could have explained the mechanism by which the force attracts, and not just the behaviour of an assumed force of attraction. :)

I don't understand. All I did was include a new figure at the bottom of the page to illustrate the field inside the cavity.

Here's how it works; the electric field is defined as force per unit charge, i.e. E = F/q. In gravity the same thing holds true. The "gravitational charge" of the gravitational force is the passive gravitational mass, m. So F/m is the gravitational field. It so happens that F/m is gravitational acceleration.

Nobody knows what the force of attraction is. Even general relativity can't tell us that.
« Last Edit: 03/12/2013 23:33:52 by Pmb »
 

lean bean

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Re: Are inertial forces real?
« Reply #55 on: 04/12/2013 18:15:42 »
I don't understand. All I did was include a new figure at the bottom of the page to illustrate the field inside the cavity.

Sorry, What I meant was... I didn't understand the whole page even before the new figure. Like many people, I may be able to do equations as such (do the equation and get the right answer), but that does not mean I understand the logic in the process. Or is that just me :) :) I'm not saying your wrong or right.


« Last Edit: 04/12/2013 18:19:36 by beany »
 

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Re: Are inertial forces real?
« Reply #56 on: 05/12/2013 02:06:14 »
I don't understand. All I did was include a new figure at the bottom of the page to illustrate the field inside the cavity.

Sorry, What I meant was... I didn't understand the whole page even before the new figure. Like many people, I may be able to do equations as such (do the equation and get the right answer), but that does not mean I understand the logic in the process. Or is that just me :) :) I'm not saying your wrong or right.
I see. I've been thinking for a while now that I should do the full fledged derivation anyway. I'll work on that tomorrow.
 

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Re: Are inertial forces real?
« Reply #57 on: 05/12/2013 04:48:49 »
Pete, I have looked at your updated page and have to say it's way above my head.
So, all I can say is, Iím obviously  not qualified to say whether your selection and use of the equations is correct or not, but it would be the cherry on the cake if you could have explained the mechanism by which the force attracts, and not just the behaviour of an assumed force of attraction. :)

I don't understand. All I did was include a new figure at the bottom of the page to illustrate the field inside the cavity.

Here's how it works; the electric field is defined as force per unit charge, i.e. E = F/q. In gravity the same thing holds true. The "gravitational charge" of the gravitational force is the passive gravitational mass, m. So F/m is the gravitational field. It so happens that F/m is gravitational acceleration.

Nobody knows what the force of attraction is. Even general relativity can't tell us that.

This may be the mechanism. As the wave ripples through the mass the contraction exerts a pull n the opposite direction. How does this relate to the stress-energy tensor? This would explain the mechanism of length contraction. The stronger the wave front the more compression is induced. In a balanced system such as the hollow planet example the effects would be of special interest and may involve unique tidal forces.

If the gravitational field increases in strength then the rate of compression increases. At near light speed a mass will encounter more gravitational waves simply by travelling trough them faster. This situation is equivalent to being in the stronger field around a mass of significant size. I agree with Pete that the gravitational field does not need a source. Gravity had to already exist during or immediately after the big bang as did everything else. It was just there along with all the other energy.
« Last Edit: 05/12/2013 06:15:25 by jeffreyH »
 

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Re: Are inertial forces real?
« Reply #58 on: 05/12/2013 11:28:21 »
Quote from: jeffreyH
This may be the mechanism. As the wave ripples through the mass the contraction exerts a pull n the opposite direction.
Jeff - If you're going to make an argument like this you should at least explain the terms that you're using. E.g. why would anybody reading your response know what this wave that you're talking about is?

Quote from: jeffreyH
In a balanced system such as the hollow planet example the effects would be of special interest and may involve unique tidal forces.
Again please define your terms. What tidal forces are you talking about? Inside the cavity, where the field that this conversation is about resides, there are no tidal forces present.
 

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Re: Are inertial forces real?
« Reply #59 on: 05/12/2013 14:52:02 »
Quote from: jeffreyH
This may be the mechanism. As the wave ripples through the mass the contraction exerts a pull n the opposite direction.
Jeff - If you're going to make an argument like this you should at least explain the terms that you're using. E.g. why would anybody reading your response know what this wave that you're talking about is?

Quote from: jeffreyH
In a balanced system such as the hollow planet example the effects would be of special interest and may involve unique tidal forces.
Again please define your terms. What tidal forces are you talking about? Inside the cavity, where the field that this conversation is about resides, there are no tidal forces present.

The wave is a gravitational wave. I don't see why there wouldn't be tidal forces as the mass surrounding the cavity would be exerting an influence on the matter in the cavity from all directions. This would be pulling the mass outward in all directions. It can be claimed that these forces cancel out but what physical evidence do we have to support that proposition.
 

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Re: Are inertial forces real?
« Reply #59 on: 05/12/2013 14:52:02 »

 

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