Re: Does physical displacement require force?

"Timo A. Nieminen" <timo@xxxxxxxxxxxxxxxxx> wrote in message
news:Pine.WNT.4.64.0705290556410.708@xxxxxxxxxxxx
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



.

Relevant Pages

  • the final complete collection of ideas
    ... Law of Conservation of Energy ... E) Outsider System vs. Insider System ... is relative to the frame of reference you are in. ...
    (sci.physics)
  • the final complete collection of ideas
    ... Law of Conservation of Energy ... E) Outsider System vs. Insider System ... is relative to the frame of reference you are in. ...
    (rec.sport.pro-wrestling)
  • the final complete collection of ideas
    ... Law of Conservation of Energy ... E) Outsider System vs. Insider System ... is relative to the frame of reference you are in. ...
    (rec.sport.football.college)
  • the final complete collection of ideas
    ... Law of Conservation of Energy ... E) Outsider System vs. Insider System ... is relative to the frame of reference you are in. ...
    (sci.skeptic)
  • the final complete collection of ideas
    ... Law of Conservation of Energy ... E) Outsider System vs. Insider System ... is relative to the frame of reference you are in. ...
    (sci.math)
Quantcast