Groups > sci.physics.relativity > #461629

Re: Why does gravity have to be transmitted through particles when gravity isn't a force in general relativity?

From	Thomas 'PointedEars' Lahn <PointedEars@web.de>
Newsgroups	sci.physics.relativity
Subject	Re: Why does gravity have to be transmitted through particles when gravity isn't a force in general relativity?
Date	2018-06-18 19:25 +0200
Organization	PointedEars Software (PES)
Message-ID	<a35d6346-6e63-0f3a-a7cd-e91c70949698@PointedEars.de> (permalink)
References	(16 earlier) <pff044$sdo$1@gioia.aioe.org> <831dafe6-ff07-44c8-bbca-3161a212b36b@googlegroups.com> <pfglqd$1dsu$1@gioia.aioe.org> <5bfd9a93-b08b-4254-ab87-843d2b050238@googlegroups.com> <9f000d1c-6bbc-4f6c-8b7f-5a6df071664d@googlegroups.com>

Show all headers | View raw

Edward Prochak wrote:
> On Saturday, June 9, 2018 at 11:00:02 AM UTC-4, kenseto wrote:
>> On Saturday, June 9, 2018 at 9:48:01 AM UTC-4, Odd Bodkin wrote:
>>> kenseto <setoken@att.net> wrote:
>>>> There is a formula for centrifugal acceleration
>>>> and that is tangential acceleration.
>>> […]
> 
> I know Odd has read this already. the problem is centrifugal acceleration
> is a vector pointing perpendicular to the tangential motion.
> IOW, centrifugal acceleration is NOT tangential to the orbit!!!!

Good grief.  Go back and pass Physics 101 first.  All of you.

           *There* *is* *no* *centrifugal* *acceleration*!

  “A body remains at rest, or in uniform motion on a straight line,
   unless a force is acting upon it.”

    —Newton’s First Law of Motion (paraphrased)

<https://en.wikipedia.org/wiki/Newton%27s_laws_of_motion>

Thus, a body in (relative) motion would continue to move uniformly on a
straight line if *no* force would act upon it.

But because there *is* a _centripetal_ force (i.e. a force directed
*towards* a center), imparting a _centripetal_ acceleration a_c on the body,
it moves on a curved trajectory.  The tangents of that trajectory are the
straight lines it would have moved on in absence of the force at that point
on the trajectory.  If the centripetal force is continuous, such as is the
case with gravity, the body goes into orbit around the center of the curve.

<https://en.wikipedia.org/wiki/Centripetal_force>

                  ^
       . -'< .    .
     '    :    `  . v
   '      :      '.                      Tangential _speed_
  v       v   F   .                     /
  :------>+<------* m    F = m a_c = m v²∕r
  '       ^   r   ^      :      \
   '      :      '       :       Centripetal acceleration:
     '.   :   .'         :       a_c = v²∕r = ω² r
         >''             :                               __
                         Centripetal force              |PE

ObRelativity:

General relativity (GR) provides the better (and also experimentally
confirmed) explanation for curved motion.  It says that energy–momentum
density is equivalent to spacetime curvature, thus spacetime geodesics of
curved spacetime, along which *inertial* (free-fall) motion must proceed
(e.g. near a massive body like a star or a planet), are not straight lines.

See also: <https://www.youtube.com/watch?v=0jjFjC30-4A>

-- 
PointedEars

Twitter: @PointedEars2
Please do not cc me. / Bitte keine Kopien per E-Mail.

Thread

(Thread has 565 articles, showing 500 — browse group in flat view)

csiph-web