| Topic: |
Science > Physics |
| User: |
"Mark Teller" |
| Date: |
28 May 2007 08:21:03 AM |
| Object: |
Does physical displacement require force? |
Is there anything in physics that suggests that an external force is
essential to move a body at rest (wrt an inertial frame) from place A
to place B (again at rest) in that ref frame?
Thanks
Mark
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| User: "Sam Wormley" |
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| Title: Re: Does physical displacement require force? |
28 May 2007 08:27:29 AM |
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Mark Teller wrote:
Is there anything in physics that suggests that an external force is
essential to move a body at rest (wrt an inertial frame) from place A
to place B (again at rest) in that ref frame?
Look carefully at Newton's three laws of motion.
http://scienceworld.wolfram.com/physics/NewtonsLaws.html
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| User: "CWatters" |
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| Title: Re: Does physical displacement require force? |
28 May 2007 10:45:34 AM |
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"Sam Wormley" <swormley1@mchsi.com> wrote in message
news:5NA6i.75439$n_.62879@attbi_s21...
Mark Teller wrote:
Is there anything in physics that suggests that an external force is
essential to move a body at rest (wrt an inertial frame) from place A
to place B (again at rest) in that ref frame?
Look carefully at Newton's three laws of motion.
http://scienceworld.wolfram.com/physics/NewtonsLaws.html
Movement from rest means acceleration and that implies a change of energy in
the system. The universe appears to conserve energy therefore energy has to
be applied to accelerate your system. I'm not sure we understand _why_
energy is conserved.
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| User: "Llanzlan Klazmon the 15th" |
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| Title: Re: Does physical displacement require force? |
28 May 2007 10:20:12 PM |
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"CWatters" <colin.watters@turnersNOSPAMoak.plus.com> wrote in
news:465af91d$0$8736$ed2619ec@ptn-nntp-reader02.plus.net:
"Sam Wormley" <swormley1@mchsi.com> wrote in message
news:5NA6i.75439$n_.62879@attbi_s21...
Mark Teller wrote:
Is there anything in physics that suggests that an external force is
essential to move a body at rest (wrt an inertial frame) from place A
to place B (again at rest) in that ref frame?
Look carefully at Newton's three laws of motion.
http://scienceworld.wolfram.com/physics/NewtonsLaws.html
Movement from rest means acceleration and that implies a change of
energy in the system. The universe appears to conserve energy therefore
energy has to be applied to accelerate your system. I'm not sure we
understand _why_ energy is conserved.
http://en.wikipedia.org/wiki/Noether's_theorem
Klazmon.
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| User: "" |
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| Title: Re: Does physical displacement require force? |
28 May 2007 11:50:49 AM |
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On 28 mai, 11:45, "CWatters" <colin.watt...@turnersNOSPAMoak.plus.com>
wrote:
"Sam Wormley" <sworml...@mchsi.com> wrote in message
news:5NA6i.75439$n_.62879@attbi_s21...
Mark Teller wrote:
Is there anything in physics that suggests that an external force is
essential to move a body at rest (wrt an inertial frame) from place A
to place B (again at rest) in that ref frame?
Look carefully at Newton's three laws of motion.
http://scienceworld.wolfram.com/physics/NewtonsLaws.html
Movement from rest means acceleration and that implies a change of energy=
in
the system. The universe appears to conserve energy therefore energy has =
to
be applied to accelerate your system. I'm not sure we understand _why_
energy is conserved.
It seems to me that we do.
It is conserved if it is not expended as work being done.
2nd Principle of Thermodynamics.
Andr=E9 Michaud
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| User: "Richard Tobin" |
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| Title: Re: Does physical displacement require force? |
28 May 2007 10:53:59 AM |
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In article <5NA6i.75439$n_.62879@attbi_s21>,
Sam Wormley <swormley1@mchsi.com> wrote:
Is there anything in physics that suggests that an external force is
essential to move a body at rest (wrt an inertial frame) from place A
to place B (again at rest) in that ref frame?
Look carefully at Newton's three laws of motion.
http://scienceworld.wolfram.com/physics/NewtonsLaws.html
And observe that though an internal force can set the parts of a body
in motion, the centre of mass of the complete body does not move.
-- Richard
--
"Consideration shall be given to the need for as many as 32 characters
in some alphabets" - X3.4, 1963.
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| User: "" |
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| Title: Re: Does physical displacement require force? |
28 May 2007 11:54:08 AM |
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On 28 mai, 09:21, Mark Teller <markteller2...@yahoo.com> wrote:
Is there anything in physics that suggests that an external force is
essential to move a body at rest (wrt an inertial frame) from place A
to place B (again at rest) in that ref frame?
Thanks
Mark
You need application of an external force to start it moving
towards B and application of an opposite force to have it
stop moving at B.
Newton's laws explain why.
Andr=E9 Michaud
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| User: "CWatters" |
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| Title: Re: Does physical displacement require force? |
28 May 2007 03:54:09 PM |
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<srp@microtec.net> wrote in message
news:1180371248.405284.92350@q69g2000hsb.googlegroups.com...
On 28 mai, 09:21, Mark Teller <markteller2...@yahoo.com> wrote:
Is there anything in physics that suggests that an external force is
essential to move a body at rest (wrt an inertial frame) from place A
to place B (again at rest) in that ref frame?
Thanks
Mark
You need application of an external force to start it moving
towards B and application of an opposite force to have it
stop moving at B.
Newton's laws explain why.
Newtons laws model how the universe works but do we know why the universe
follows Newtons laws? What's the fundamental reason why energy is conserved
and can't be used up for example.
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| User: "" |
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| Title: Re: Does physical displacement require force? |
28 May 2007 05:17:36 PM |
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On 28 mai, 16:54, "CWatters" <colin.watt...@turnersNOSPAMoak.plus.com>
wrote:
<s...@microtec.net> wrote in message
news:1180371248.405284.92350@q69g2000hsb.googlegroups.com...
On 28 mai, 09:21, Mark Teller <markteller2...@yahoo.com> wrote:
Is there anything in physics that suggests that an external force is
essential to move a body at rest (wrt an inertial frame) from place A
to place B (again at rest) in that ref frame?
Thanks
Mark
You need application of an external force to start it moving
towards B and application of an opposite force to have it
stop moving at B.
Newton's laws explain why.
Newtons laws model how the universe works but do we know why the universe
follows Newtons laws?
I don't think we do from this perspective. We observe that it does
and
that's about it, generally speaking. No one knows the fundamental
cause yet.
What's the fundamental reason why energy is conserved
and can't be used up for example.
Well, the all encompassing statement that the total complement
of energy in the universe is conserved is more of a postulate
than a verified fact.
This idea was first aired hundreds of years ago as astronomers
observed that the planets seemed to be perfectly stable on
their orbits.
How could this stability be explained (then) otherwise than
by concluding that no expenditure of energy was involved
in maintaining the planets on their orbits. The alternative
seemed to be that if energy was expended, then the planets
would eventually slow down and ultimately fall into the Sun.
They could just as well have concluded that energy was
expended as the planets constantly changed direction as
they followed their orbits but that the expended energy
was also constantly replenished by the force of gravity
that was constantly accelerating them.
But the 2nd principle of thermodynamics had not yet
come to light then, so it could not influence nor cause
them to cast doubt on their first conclusion.
We know more now about freely rotating bodies and
have on record that the rotation of both the Pioneer 10
and 11 on their axis to maintain their antena directed
towards the Earth have been "unexplainedly" slowing
down. (unexplainable in regard to the postulate that
rotation involves no expenditure of energy).
What is the difference between the Pioneers motion
and stable planetary motion ?
Simply that the Pioneers have been mechanically set
onto their hyperbolic trajectories and rotating motion
by artificial means, that ceased to apply their force as
soon as the initial impulse ended, while the planets are
permanently subjected to a force.
The 2nd principle of Thermodynamics mandates that
for any change of state requires expenditure of energy.
Changing direction is a change of state even in classical
mechanics, except for the permanent change in direction
of planets on their orbits. This idea has been extended to
all rotating motion and all translation motion without
ever being reconsidered, whether or not a sustaining
force is acting or not.
But note that such thinking about reconsideration is
very heavily frowned upon by orthodox physics.
Andr=E9 Michaud
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| User: "Sam Wormley" |
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| Title: Re: Does physical displacement require force? |
28 May 2007 07:58:49 PM |
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wrote:
Well, the all encompassing statement that the total complement
of energy in the universe is conserved is more of a postulate
than a verified fact.
Noether's theorem demands that the conservation of energy is a
consequence of invariance under time translations. Observation
confirms the conservation of energy.
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| User: "" |
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| Title: Re: Does physical displacement require force? |
28 May 2007 10:07:50 PM |
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On 28 mai, 20:58, Sam Wormley <sworml...@mchsi.com> wrote:
s...@microtec.net wrote:
Well, the all encompassing statement that the total complement
of energy in the universe is conserved is more of a postulate
than a verified fact.
Noether's theorem demands that the conservation of energy is a
consequence of invariance under time translations. Observation
confirms the conservation of energy.
Not in the case of both Pioneers rotation about their
antena axis, it seems to me. This case precisely
contradicts conservation.
The only man made bodies to be left rotating in deep space
long enough after initial impulse for the "anomaly" to be
noted and measured.
I tend to trust experimental reality more than any theory that
comes in apparent contradiction.
Andr=E9 Michaud
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| User: "Sam Wormley" |
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| Title: Re: Does physical displacement require force? |
28 May 2007 10:22:15 PM |
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wrote:
On 28 mai, 20:58, Sam Wormley <sworml...@mchsi.com> wrote:
s...@microtec.net wrote:
Well, the all encompassing statement that the total complement
of energy in the universe is conserved is more of a postulate
than a verified fact.
Noether's theorem demands that the conservation of energy is a
consequence of invariance under time translations. Observation
confirms the conservation of energy.
Not in the case of both Pioneers rotation about their
antena axis, it seems to me. This case precisely
contradicts conservation.
Seem to me that the Pioneers' anomalous accelerations are due to
processes explained by classical mechanics, especially since
all bodies of the solar system don't share the anomalous acceleration.
The only man made bodies to be left rotating in deep space
long enough after initial impulse for the "anomaly" to be
noted and measured.
I tend to trust experimental reality more than any theory that
comes in apparent contradiction.
André Michaud
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| User: "" |
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| Title: Re: Does physical displacement require force? |
29 May 2007 12:47:04 AM |
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On 28 mai, 23:22, Sam Wormley <sworml...@mchsi.com> wrote:
s...@microtec.net wrote:
On 28 mai, 20:58, Sam Wormley <sworml...@mchsi.com> wrote:
s...@microtec.net wrote:
Well, the all encompassing statement that the total complement
of energy in the universe is conserved is more of a postulate
than a verified fact.
Noether's theorem demands that the conservation of energy is a
consequence of invariance under time translations. Observation
confirms the conservation of energy.
Not in the case of both Pioneers rotation about their
antena axis, it seems to me. This case precisely
contradicts conservation.
Seem to me that the Pioneers' anomalous accelerations are
due to processes explained by classical mechanics,
especially since all bodies of the solar system don't share
the anomalous acceleration.
I was not talking about the so-called anomalous acceleration,
which by the way has not been explained either by classical
mechanics nor by GR.
I was talking about the second anomaly that was noted.
That regarding the so-called anomalous slowing down of
the spin of the crafts about their axis.
Which has not been explained either by CM nor by GR
either.
Ref:
John D. Anderson et al., Study of the anomalous acceleration
of Pioneer 10 and 11, gr-qc/0104064, 10 Mar 2005
The only man made bodies to be left rotating in deep space
long enough after initial impulse for the "anomaly" to be
noted and measured.
I tend to trust experimental reality more than any theory that
comes in apparent contradiction.
Andr=E9 Michaud
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| User: "CWatters" |
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| Title: Re: Does physical displacement require force? |
29 May 2007 04:33:01 AM |
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<srp@microtec.net> wrote in message
news:1180417624.131120.41190@q75g2000hsh.googlegroups.com...
I was talking about the second anomaly that was noted.
That regarding the so-called anomalous slowing down of
the spin of the crafts about their axis.
Interesting. I hadn't heard about that one.
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| User: "" |
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| Title: Re: Does physical displacement require force? |
29 May 2007 09:30:55 AM |
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On 29 mai, 05:33, "CWatters" <colin.watt...@turnersNOSPAMoak.plus.com>
wrote:
<s...@microtec.net> wrote in message
news:1180417624.131120.41190@q75g2000hsh.googlegroups.com...
I was talking about the second anomaly that was noted.
That regarding the so-called anomalous slowing down of
the spin of the crafts about their axis.
Interesting. I hadn't heard about that one.
Very interesting indeed, since it directly contradicts
the universality of absolute energy conservation.
But the 2nd principle of thermo much more fundamentally
contradicts it also, since it mandates that no change of
state can occur in a closed system without the expenditure
of energy (work).
Sam was under the impression that the first anomaly, that
regarding the so-called anomalous acceleration directed
towards the Sun had been dealt with with classical mechanics,
but this is impossible since, just as with GR, this would mean
that a means had been found to explain in these theories
that the crafts have become slightly more massive as they
reached space and maintained that increased mass as they
followed their hyperbolic trajectories.
Impossible predicament since rest mass is deemed
invariant in both CM and GR.
Andr=E9 Michaud
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| User: "Sam Wormley" |
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| Title: Re: Does physical displacement require force? |
29 May 2007 10:48:50 AM |
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wrote:
On 29 mai, 05:33, "CWatters" <colin.watt...@turnersNOSPAMoak.plus.com>
wrote:
<s...@microtec.net> wrote in message
news:1180417624.131120.41190@q75g2000hsh.googlegroups.com...
I was talking about the second anomaly that was noted.
That regarding the so-called anomalous slowing down of
the spin of the crafts about their axis.
Interesting. I hadn't heard about that one.
Very interesting indeed, since it directly contradicts
the universality of absolute energy conservation.
But the 2nd principle of thermo much more fundamentally
contradicts it also, since it mandates that no change of
state can occur in a closed system without the expenditure
of energy (work).
Sam was under the impression that the first anomaly, that
regarding the so-called anomalous acceleration directed
towards the Sun had been dealt with with classical mechanics,
but this is impossible since, just as with GR, this would mean
that a means had been found to explain in these theories
that the crafts have become slightly more massive as they
reached space and maintained that increased mass as they
followed their hyperbolic trajectories.
Impossible predicament since rest mass is deemed
invariant in both CM and GR.
André Michaud
You should ask yourself, André, "knowing that the conservation of
energy reigns supreme in the universe, how am I being fooled"?
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| User: "" |
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| Title: Re: Does physical displacement require force? |
29 May 2007 11:02:01 AM |
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On 29 mai, 11:48, Sam Wormley <sworml...@mchsi.com> wrote:
s...@microtec.net wrote:
On 29 mai, 05:33, "CWatters" <colin.watt...@turnersNOSPAMoak.plus.com>
wrote:
<s...@microtec.net> wrote in message
news:1180417624.131120.41190@q75g2000hsh.googlegroups.com...
I was talking about the second anomaly that was noted.
That regarding the so-called anomalous slowing down of
the spin of the crafts about their axis.
Interesting. I hadn't heard about that one.
Very interesting indeed, since it directly contradicts
the universality of absolute energy conservation.
But the 2nd principle of thermo much more fundamentally
contradicts it also, since it mandates that no change of
state can occur in a closed system without the expenditure
of energy (work).
Sam was under the impression that the first anomaly, that
regarding the so-called anomalous acceleration directed
towards the Sun had been dealt with with classical mechanics,
but this is impossible since, just as with GR, this would mean
that a means had been found to explain in these theories
that the crafts have become slightly more massive as they
reached space and maintained that increased mass as they
followed their hyperbolic trajectories.
Impossible predicament since rest mass is deemed
invariant in both CM and GR.
You should ask yourself, Andr=E9, "knowing that the conservation of
energy reigns supreme in the universe, how am I being fooled"?
:-)
Maybe you should ask yourself "knowing that current
experimental evidence contradicts centuries old theories,
cooked up when less was known about physical reality,
how am I being fooled?"
Andr=E9 Michaud
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| User: "Sue..." |
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| Title: Re: Does physical displacement require force? |
28 May 2007 04:55:28 PM |
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On May 28, 10:21 am, Mark Teller <markteller2...@yahoo.com> wrote:
Is there anything in physics that suggests that an external force is
essential to move a body at rest (wrt an inertial frame) from place A
to place B (again at rest) in that ref frame?
Thanks
Mark
The Wikipedia definition for IFR gurantees the
motion can only be the result of a force.
<< Hence, within the inertial frame, an object or body
accelerates only when a physical force is applied, >>
http://en.wikipedia.org/wiki/Inertial_frame_of_reference
Whether that is a fair specification for an inertial interaction
might be open to debate.
Tajmar and de Matos concluded: <<... that the presence of
Cooperpairs inside the superconductor leads to a deviation
from the equivalence principle and from the classical
gravitational Larmor theorem. A rigid reference frame
mixed with non-coherent and coherent matter is not equivalent
to a rigid reference frame made of normal matter alone, with
respect to its inertial and gravitational properties.
However, in the case of a Bose-Einstein condensate
where we have only coherent matter, Equ. (13) transforms
into the usual expression for normal matter and the
equivalence principle is again conserved. >>
http://arxiv.org/abs/gr-qc/0603032
http://www.esa.int/SPECIALS/GSP/SEM0L6OVGJE_0.html
Sue...
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| User: "Timo A. Nieminen" |
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28 May 2007 03:02:57 PM |
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On Mon, 28 May 2007, Mark Teller wrote:
Is there anything in physics that suggests that an external force is
essential to move a body at rest (wrt an inertial frame) from place A
to place B (again at rest) in that ref frame?
Sounds like you are talking about instantaneous teleportation.
OK, ask (1) is energy conserved, (2) momentum, (3) angular momentum.
In an inertial frame where the body is at rest both before and after,
clearly we can answer "yes" to 1, 2, and 3.
The problems come when we consider inertial frames where the body is
moving both before and after. Most notably, for (3), we must usually say
"no" - the expection is the special case when the object re-appears along
its original line of motion.
Perhaps more subtly, the relativity of simultaneity means that while you
can get 1, 2, 3 conserved in some frames, the act of "instantaneous"
teleportation will only be instantaneous in some frames, and in other
frames, the object will reappear before disappearing, violating
conservation of energy, and in others will not reappear immediately,
likewise violating conservation of energy.
--
Timo Nieminen - Home page: http://www.physics.uq.edu.au/people/nieminen/
E-prints: http://eprint.uq.edu.au/view/person/Nieminen,_Timo_A..html
Shrine to Spirits: http://www.users.bigpond.com/timo_nieminen/spirits.html
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| User: "Greg Neill" |
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| Title: Re: Does physical displacement require force? |
29 May 2007 08:11:28 AM |
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"Timo A. Nieminen" <timo@physics.uq.edu.au> wrote in message
news:Pine.WNT.4.64.0705290556410.708@serene.st...
On Mon, 28 May 2007, Mark Teller wrote:
Is there anything in physics that suggests that an external force is
essential to move a body at rest (wrt an inertial frame) from place A
to place B (again at rest) in that ref frame?
Sounds like you are talking about instantaneous teleportation.
OK, ask (1) is energy conserved, (2) momentum, (3) angular momentum.
In an inertial frame where the body is at rest both before and after,
clearly we can answer "yes" to 1, 2, and 3.
Careful there. Energy comes in various forms, and the
energy of a system is not all tied up in mass or momentum!
If you shift the location of something you can change potential
energy. You will also change the center of mass of the system,
which is equivalent to moving the ensemble as far as external
observers are concerned. You will also change the angular
momentum of the system for any frame of reference that happens
to be in motion w.r.t. the object.
The problems come when we consider inertial frames where the body is
moving both before and after. Most notably, for (3), we must usually say
"no" - the expection is the special case when the object re-appears along
its original line of motion.
It requires only that there exist other objects in the
universe for teleportation without force (or energy
expediture) to cause infractions of the laws.
Perhaps more subtly, the relativity of simultaneity means that while you
can get 1, 2, 3 conserved in some frames, the act of "instantaneous"
teleportation will only be instantaneous in some frames, and in other
frames, the object will reappear before disappearing, violating
conservation of energy, and in others will not reappear immediately,
likewise violating conservation of energy.
--
Timo Nieminen - Home page: http://www.physics.uq.edu.au/people/nieminen/
E-prints: http://eprint.uq.edu.au/view/person/Nieminen,_Timo_A..html
Shrine to Spirits: http://www.users.bigpond.com/timo_nieminen/spirits.html
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| User: "boson boss" |
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| Title: Re: Does physical displacement require force? |
29 May 2007 11:49:50 AM |
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On May 29, 3:11 pm, "Greg Neill" <gneill...@OVEsympatico.ca> wrote:
"Timo A. Nieminen" <t...@physics.uq.edu.au> wrote in messagenews:Pine.WNT.4.64.0705290556410.708@serene.st...
On Mon, 28 May 2007, Mark Teller wrote:
Is there anything in physics that suggests that an external force is
essential to move a body at rest (wrt an inertial frame) from place A
to place B (again at rest) in that ref frame?
Sounds like you are talking about instantaneous teleportation.
OK, ask (1) is energy conserved, (2) momentum, (3) angular momentum.
In an inertial frame where the body is at rest both before and after,
clearly we can answer "yes" to 1, 2, and 3.
Careful there. Energy comes in various forms, and the
energy of a system is not all tied up in mass or momentum!
Can we make a some kind of orienting map of what kind of energy can be
transduced into kinetic energy and back into something (probably some
potential state)? We can at least a little, and there are rules.
If you shift the location of something you can change potential
energy. You will also change the center of mass of the system,
which is equivalent to moving the ensemble as far as external
observers are concerned. You will also change the angular
momentum of the system for any frame of reference that happens
to be in motion w.r.t. the object.
The problems come when we consider inertial frames where the body is
moving both before and after. Most notably, for (3), we must usually say
"no" - the expection is the special case when the object re-appears along
its original line of motion.
It requires only that there exist other objects in the
universe for teleportation without force (or energy
expediture) to cause infractions of the laws.
Perhaps more subtly, the relativity of simultaneity means that while you
can get 1, 2, 3 conserved in some frames, the act of "instantaneous"
teleportation will only be instantaneous in some frames, and in other
frames, the object will reappear before disappearing, violating
conservation of energy, and in others will not reappear immediately,
likewise violating conservation of energy.
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| User: "boson boss" |
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| Title: Re: Does physical displacement require force? |
28 May 2007 04:11:31 PM |
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On May 28, 10:02 pm, "Timo A. Nieminen" <t...@physics.uq.edu.au>
wrote:
On Mon, 28 May 2007, Mark Teller wrote:
Is there anything in physics that suggests that an external force is
essential to move a body at rest (wrt an inertial frame) from place A
to place B (again at rest) in that ref frame?
Sounds like you are talking about instantaneous teleportation.
OK, ask (1) is energy conserved, (2) momentum, (3) angular momentum.
In an inertial frame where the body is at rest both before and after,
clearly we can answer "yes" to 1, 2, and 3.
The problems come when we consider inertial frames where the body is
moving both before and after. Most notably, for (3), we must usually say
"no" - the expection is the special case when the object re-appears along
its original line of motion.
Perhaps more subtly, the relativity of simultaneity means that while you
can get 1, 2, 3 conserved in some frames, the act of "instantaneous"
teleportation will only be instantaneous in some frames, and in other
frames, the object will reappear before disappearing, violating
conservation of energy, and in others will not reappear immediately,
likewise violating conservation of energy.
So this was about teleportation? I think the question is: "Is there
anything in physics that suggests that an external force is essential
to move a body". And the answer is actually no... because going down
to so fundamental translates into "motions of energy happen" and
nothing more. Thats why I'd disregard question and go for a random
improvement of topic. Such as "teleportation" and examining something
concrete like statement "force exists". So... it does? Well, I guess
that "interaction" is just that and it has some rules and ingredients
which seem fixed with extreme prejudice.
As for the "teleportation" ... it sounds cool. MAybe in magick tricks
though - ("pss there was a stunt double") better. What kind of energy
are we talking about when moving energy across distance? Is that
teleportation? Oh well.
:-))
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| User: "Mark Teller" |
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| Title: Re: Does physical displacement require force? |
29 May 2007 05:42:08 AM |
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On May 29, 1:02 am, "Timo A. Nieminen" <t...@physics.uq.edu.au> wrote:
On Mon, 28 May 2007, Mark Teller wrote:
Is there anything in physics that suggests that an external force is
essential to move a body at rest (wrt an inertial frame) from place A
to place B (again at rest) in that ref frame?
Sounds like you are talking about instantaneous teleportation.
OK, ask (1) is energy conserved, (2) momentum, (3) angular momentum.
In an inertial frame where the body is at rest both before and after,
clearly we can answer "yes" to 1, 2, and 3.
The problems come when we consider inertial frames where the body is
moving both before and after. Most notably, for (3), we must usually say
"no" - the expection is the special case when the object re-appears along
its original line of motion.
Perhaps more subtly, the relativity of simultaneity means that while you
can get 1, 2, 3 conserved in some frames, the act of "instantaneous"
teleportation will only be instantaneous in some frames, and in other
frames, the object will reappear before disappearing, violating
conservation of energy, and in others will not reappear immediately,
likewise violating conservation of energy.
--
Timo Nieminen - Home page:http://www.physics.uq.edu.au/people/nieminen/
E-prints:http://eprint.uq.edu.au/view/person/Nieminen,_Timo_A..html
Shrine to Spirits:http://www.users.bigpond.com/timo_nieminen/spirits.html
Thanks.
I certainly didnt mean teleportation. However as you mentioned, it is
the fact that conservation of energy, momentum and angular momentum
alone are not enough to preclude that is interesting to me.
Am I right in saying that Lagrangian and Hamiltonian mechanics is
based on the above conservation principle?
Then however would you explain the shift in centre of mass. Is it
acceptable in Classical mechanics?
Thanks.
Mark
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| User: "Ben C" |
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| Title: Re: Does physical displacement require force? |
29 May 2007 08:56:46 AM |
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On 2007-05-29, Mark Teller <markteller2000@yahoo.com> wrote:
On May 29, 1:02 am, "Timo A. Nieminen" <t...@physics.uq.edu.au> wrote:
[...]
Perhaps more subtly, the relativity of simultaneity means that while you
can get 1, 2, 3 conserved in some frames, the act of "instantaneous"
teleportation will only be instantaneous in some frames, and in other
frames, the object will reappear before disappearing, violating
conservation of energy, and in others will not reappear immediately,
likewise violating conservation of energy.
--
Timo Nieminen - Home page:http://www.physics.uq.edu.au/people/nieminen/
E-prints:http://eprint.uq.edu.au/view/person/Nieminen,_Timo_A..html
Shrine to Spirits:http://www.users.bigpond.com/timo_nieminen/spirits.html
Thanks.
I certainly didnt mean teleportation. However as you mentioned, it is
the fact that conservation of energy, momentum and angular momentum
alone are not enough to preclude that is interesting to me.
I found that interesting too, but note that it only precludes
_instantaneous_ teleportation. Teleporting at finite speed (the speed of
light say) might be OK.
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| User: "Timo A. Nieminen" |
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| Title: Re: Does physical displacement require force? |
29 May 2007 01:53:22 PM |
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On Tue, 29 May 2007, Mark Teller wrote:
On May 29, 1:02 am, "Timo A. Nieminen" <t...@physics.uq.edu.au> wrote:
On Mon, 28 May 2007, Mark Teller wrote:
Is there anything in physics that suggests that an external force is
essential to move a body at rest (wrt an inertial frame) from place A
to place B (again at rest) in that ref frame?
Sounds like you are talking about instantaneous teleportation.
OK, ask (1) is energy conserved, (2) momentum, (3) angular momentum.
In an inertial frame where the body is at rest both before and after,
clearly we can answer "yes" to 1, 2, and 3.
The problems come when we consider inertial frames where the body is
moving both before and after. Most notably, for (3), we must usually say
"no" - the expection is the special case when the object re-appears along
its original line of motion.
Perhaps more subtly, the relativity of simultaneity means that while you
can get 1, 2, 3 conserved in some frames, the act of "instantaneous"
teleportation will only be instantaneous in some frames, and in other
frames, the object will reappear before disappearing, violating
conservation of energy, and in others will not reappear immediately,
likewise violating conservation of energy.
I certainly didnt mean teleportation. However as you mentioned, it is
the fact that conservation of energy, momentum and angular momentum
alone are not enough to preclude that is interesting to me.
Conservation of momentum means you can't do it without teleportation (with
no external force, you can't get the momentum you'd need to have the
centre of mass moving at some speed > 0).
The conservation laws in _some_ frames are not enough to preclude it.
Insisting that they hold in _all_ inertial frames is enough to do so.
Am I right in saying that Lagrangian and Hamiltonian mechanics is
based on the above conservation principle?
No. Newton's laws are all about conservation of momentum, and conservation
of angular momentum can be obtained from them too. L/H mechanics and
Newton's laws can be gotten from each other. However, classical mechanics,
however expressed, doesn't give us conservation of energy, as only
mechanical energy is considered - what does classical mechanics say about,
e.g., chemical energy?
But you could say classical mechanics is based on conservation of momentum
and angular momentum. (Or that conservation of momentum and angular
momentum is a concise summary of the principles of classical mechanics -
which one is based on which one?)
Then however would you explain the shift in centre of mass. Is it
acceptable in Classical mechanics?
In a Newtonian universe, teleportation of objects appears compatible with
Newton's laws, as long as the teleportation conserves momentum. No
conservation of angular momentum. Can one then build a perpetual motion
machine with a teleporting ball and a lever (or two balls and a lever)?
But if you want to look at a real, working system along the lines of your
original question: cats. Cats successfully change their orientation in
space, starting from rest, finishing at rest, with no external torques.
--
Timo Nieminen - Home page: http://www.physics.uq.edu.au/people/nieminen/
E-prints: http://eprint.uq.edu.au/view/person/Nieminen,_Timo_A..html
Shrine to Spirits: http://www.users.bigpond.com/timo_nieminen/spirits.html
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| User: "Mark Teller" |
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| Title: Re: Does physical displacement require force? |
08 Jun 2007 02:20:13 AM |
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But if you want to look at a real, working system along the lines of your
original question: cats. Cats successfully change their orientation in
space, starting from rest, finishing at rest, with no external torques.
Changing orientation in space.....
True that cats or even divers do it skillfully.
Consider an object at rest consisting of a square box and a particle
lying in its diagonal (for brevity sake, lets talk 2D) off centre. At
an instant the particle splits into two and flies off in opposite
directions perpendicular to the diagonal. It hits the walls and joins
back again at the diagonal, this time offset in the opposite
direction.
Orientation changed, centre of mass at rest.
Now what would happen if we fill the box with a fluid?
There would of course be some energy loss.
Would it be-------orientation changed, centre of mass at rest, energy
lost?
Thanks
Mark
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| User: "Edward Green" |
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| Title: Re: Does physical displacement require force? |
11 Jun 2007 03:42:19 PM |
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On Jun 8, 3:20 am, Mark Teller <markteller2...@yahoo.com> wrote:
But if you want to look at a real, working system along the lines of your
original question: cats. Cats successfully change their orientation in
space, starting from rest, finishing at rest, with no external torques.
Changing orientation in space.....
True that cats or even divers do it skillfully.
Consider an object at rest consisting of a square box and a particle
lying in its diagonal (for brevity sake, lets talk 2D) off centre. At
an instant the particle splits into two and flies off in opposite
directions perpendicular to the diagonal. It hits the walls and joins
back again at the diagonal, this time offset in the opposite
direction.
Orientation changed, centre of mass at rest.
That's a neat, atypical example (taking cats to be typical).
We might think, reductionistically, that any COM preserving
rearrangement of a static configuration of matter into a second static
configuration of matter is permitted: "reorientations" are simply a
special case where the final configuration can be mapped into the
initial configuration by a rotation.
Now what would happen if we fill the box with a fluid?
There would of course be some energy loss.
Would it be-------orientation changed, centre of mass at rest, energy
lost?
Sure... why not? Cats do not have frictionless innards.
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| User: "Edward Green" |
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| Title: Re: Does physical displacement require force? |
03 Jun 2007 08:56:43 PM |
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On May 29, 2:53 pm, "Timo A. Nieminen" <t...@physics.uq.edu.au> wrote:
But if you want to look at a real, working system along the lines of your
original question: cats. Cats successfully change their orientation in
space, starting from rest, finishing at rest, with no external torques.
Yes -- I've thought about the cat question. I came to the conclusion
that the reason this is possible with angular displacement but not
with linear displacement is that we can independently vary the angular
inertia (aka moment of inertia) of parts of the body, whereas we
certainly can't independently vary the linear inertia, aka inertial
mass.
If we could, the linear scheme would go something like -- let the
leading mass be B, the trailing A, B > A. Pull in the tail mass,
which comes in farther than the head mass retreats, magically alter
the masses so that the leading body now masses A, the trailing B, and
extend the inchworm: the head now moves out farther than the tail,
and the think inches forward.
Possible by extending and retracting parts in the angular case,
impossible in the linear case.
Another way of expressing this seems to be that if a body, of the same
form before and after the displacement, relocates, the COM must have
been in motion some time inbetween, whereas there is no concept of
"angular center of mass" to get us in trouble in the reorientation.
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| User: "boson boss" |
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| Title: Re: Does physical displacement require force? |
05 Jun 2007 10:47:25 AM |
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On Jun 4, 3:56 am, Edward Green <spamspamsp...@netzero.com> wrote:
On May 29, 2:53 pm, "Timo A. Nieminen" <t...@physics.uq.edu.au> wrote:
But if you want to look at a real, working system along the lines of your
original question: cats. Cats successfully change their orientation in
space, starting from rest, finishing at rest, with no external torques.
Yes -- I've thought about the cat question. I came to the conclusion
that the reason this is possible with angular displacement but not
with linear displacement is that we can independently vary the angular
inertia (aka moment of inertia) of parts of the body, whereas we
certainly can't independently vary the linear inertia, aka inertial
mass.
If we could, the linear scheme would go something like -- let the
leading mass be B, the trailing A, B > A. Pull in the tail mass,
which comes in farther than the head mass retreats, magically alter
the masses so that the leading body now masses A, the trailing B, and
extend the inchworm: the head now moves out farther than the tail,
and the think inches forward.
Possible by extending and retracting parts in the angular case,
impossible in the linear case.
Another way of expressing this seems to be that if a body, of the same
form before and after the displacement, relocates, the COM must have
been in motion some time inbetween, whereas there is no concept of
"angular center of mass" to get us in trouble in the reorientation.
I don't know what you just wrote (little time at hand), but I
understand the thing about inner energy of cats. But also, cats push
themselves off the ground, and since it is action/reaction we can say
something is "external" about this.
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| User: "Edward Green" |
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| Title: Re: Does physical displacement require force? |
05 Jun 2007 11:36:01 AM |
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On Jun 5, 11:47 am, boson boss <junker...@gmail.com> wrote:
I don't know what you just wrote (little time at hand), but I
understand the thing about inner energy of cats. But also, cats push
themselves off the ground, and since it is action/reaction we can say
something is "external" about this
The point is that a cat -- or any sufficiently flexible object, but
cats are famous for it -- can reorient themselves without any external
force whatsoever. "No external force" mean in mid-air, with any
contact with the ground. (Real cats may make use of air resistance,
but there is no requirement: satelites can be reoriented in vacuum).
This is different than the behavior of the center of mass of the
object: at rest in some inertial frame it cannot be moved at all in
the absense of external forces.
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