According to Newton, an orbiting body feels a centrifugal
force from gravity, like a bola, a rock on a rope. This
is a striking difference from general relativity, where a
body in free fall is inertial.

To my knowledge, this property has never been tested.
But it must apply to satellites in orbit around earth.
Could an experiment be performed on the space station
to test this prediction? Or is the effect too small to detect
with current technology?

--
Rich

On 15-Oct-21 12:51 pm, RichD wrote:
> According to Newton, an orbiting body feels a centrifugal
> force from gravity, like a bola, a rock on a rope. This
> is a striking difference from general relativity, where a
> body in free fall is inertial.
>
> To my knowledge, this property has never been tested.
> But it must apply to satellites in orbit around earth.
> Could an experiment be performed on the space station
> to test this prediction? Or is the effect too small to detect
> with current technology?
>
> --
> Rich
>

Leaving aside the differences between GR and Newton at high velocities
and masses, these are different mathematical formulations of the same
thing. Outside those more extreme scenarios, they cannot be
distinguished by experiment.

Sylvia.

That is rotation's weight not a force weight...
A centrifuge is not a creator of its own force.

Mitchell Raemsch

Op 15-okt.-2021 om 03:51 schreef RichD:
> According to Newton, an orbiting body feels a centrifugal
> force from gravity, like a bola, a rock on a rope. This
> is a striking difference from general relativity, where a
> body in free fall is inertial.
>
> To my knowledge, this property has never been tested.
> But it must apply to satellites in orbit around earth.
> Could an experiment be performed on the space station
> to test this prediction? Or is the effect too small to detect
> with current technology?
>
> --
> Rich
>

Think about this.
According to Newton, an orbiting object does not
"feel a centrifugal force from gravitity." It feels
nothing. That has been tested.
A satellite in orbit (aka free fall) is not on a rope.
If you would attach a rope to an already circularly
orbiting satellite, there would be no tension in that
rope.
With a rope you could imagine making it go "faster",
there *would* be a tension in the rope, and the
satellite would be no longer in free fall.
A rock on a rope is not in orbit around your hand.

Dirk Vdm

RichD <r_delaney2001@yahoo.com> wrote:
> According to Newton, an orbiting body feels a centrifugal
> force from gravity, like a bola, a rock on a rope.

This is a mistake even at the basic freshman classical physics level.
No body feels a centrifugal force. The rock does feel the force from the
rope. That’s a centripetal force, not a centrifugal force. If you sit on a
merry-go-round, there is a force of friction that is pulling your rear end
toward the center of the carousel; that’s a centripetal force, not a
centrifugal force. Nor do you feel an outward force on your head. What you
DO feel is the unaccustomed sensation of having to use your abdominal
muscles to keep your head above your rear end, which you don’t normally
have to do in linear motion. That’s action required of your abdominal
muscles to deviate the path of your head from a straight, tangential line.

There are many cases where we confuse a change in sensation in our bodies
with some (fabricated) force in the opposite direction.

When an elevator starts to descend, you FEEL lighter, when in fact the
downward force on you due to gravity has not changed one bit. Instead,
what’s changed is the UPWARD pressure the elevator floor exerts on your
feet. You are accustomed to that upward force being equal to your weight in
equilibrium, and now that the equilibrium has been upset, your mind makes
the mistake of assuming that your weight has also changed, just because the
upward force on your feet has lowered.

> This
> is a striking difference from general relativity, where a
> body in free fall is inertial.
>
> To my knowledge, this property has never been tested.
> But it must apply to satellites in orbit around earth.
> Could an experiment be performed on the space station
> to test this prediction? Or is the effect too small to detect
> with current technology?
>
> --
> Rich
>

--
Odd Bodkin -- maker of fine toys, tools, tables

Sylvia Else wrote:

>> To my knowledge, this property has never been tested.
>> But it must apply to satellites in orbit around earth.
>> Could an experiment be performed on the space station to test this
>> prediction? Or is the effect too small to detect with current
>> technology? -- Rich
>
> Leaving aside the differences between GR and Newton at high velocities
> and masses, these are different mathematical formulations of the same
> thing. Outside those more extreme scenarios, they cannot be
> distinguished by experiment.

you can, when the speed is different from the world line. Faster gives
elongated orbits.

On Friday, October 15, 2021 at 9:34:00 AM UTC-7, Kendale Gross wrote:
> Sylvia Else wrote:
>
> >> To my knowledge, this property has never been tested.

"Maxwell's electrodynamics proceeds in the same unusual way already analyzed in studying his electrostatics. Under the influence of hypotheses which remain vague and undefined in his mind, Maxwell sketches a theory which he never completes, he does not even bother to remove contradictions from it; then he starts changing this theory, he imposes on it essential modifications which he does not notify to his reader; the latter tries in vain to fix the fugitive and intangible thought of the author; just when he thinks he has got it, even the parts of the doctrine dealing with the best studied phenomena are seen to vanish. And yet this strange and disconcerting method led Maxwell to the electromagnetic theory of light!" (Duhem, 1902).

Duhem was an old crank too and he also had a cat name Lester and played with hot wheels and did the Wobbly (a dance popular at the time)

On October 15, Dirk Van de moortel wrote:
>> According to Newton, an orbiting body feels a centrifugal
>> force from gravity, like a bola, a rock on a rope. This
>> is a striking difference from general relativity, where a
>> body in free fall is inertial.
>> To my knowledge, this property has never been tested.
>> But it must apply to satellites in orbit around earth.
>> Could an experiment be performed on the space station
>> to test this prediction?
>
> Think about this.
> According to Newton, an orbiting object does not
> "feel a centrifugal force from gravitity." It feels
> nothing. That has been tested.
> A satellite in orbit (aka free fall) is not on a rope.
> A rock on a rope is not in orbit around your hand.

The origin of this idea stems from describing Newtonian gravity
as a central force (on the planets, typically). The physics of a bola
is described the same way. It's misleading, to say the least.

On second and third thought, I admit error here. They are different.
But the error is subtle, and no one has explained the discrepancy.

THINK:
The rock travels in a circular trajectory, around the ground point
of the rope.
It is driven by a centripetal force, always perpendicular
to its velocity.
It moves at constant speed.
It moves with constant angular acceleration.

AND:
The satellite travels in a circular trajectory, around the earth center.
It is driven by a centripetal force - gravity - always perpendicular
to its velocity.
It moves at constant speed.
It moves with constant angular acceleration.

Finally:
There is tension in the rope, which transmits the force to the rock,
which experiences internal stresses (the centrifugal force, loosely
speaking), hence strain, in the direction along the rope.
The strain is measurable, in principle.

Then, why is there no such centrifugal force felt by the satellite?

Waving your hands and shouting "They're very different!" is mere
hand waving. Asserting a fact does not explain the fact.

There is an explanation. A challenge to the student: can you offer one?

PS Your claim that this has been tested is silly.

--
Rich

RichD <r_delaney2001@yahoo.com> wrote:
> On October 15, Dirk Van de moortel wrote:
>>> According to Newton, an orbiting body feels a centrifugal
>>> force from gravity, like a bola, a rock on a rope. This
>>> is a striking difference from general relativity, where a
>>> body in free fall is inertial.
>>> To my knowledge, this property has never been tested.
>>> But it must apply to satellites in orbit around earth.
>>> Could an experiment be performed on the space station
>>> to test this prediction?
>>
>> Think about this.
>> According to Newton, an orbiting object does not
>> "feel a centrifugal force from gravitity." It feels
>> nothing. That has been tested.
>> A satellite in orbit (aka free fall) is not on a rope.
>> A rock on a rope is not in orbit around your hand.
>
> The origin of this idea stems from describing Newtonian gravity
> as a central force (on the planets, typically). The physics of a bola
> is described the same way. It's misleading, to say the least.
>
> On second and third thought, I admit error here. They are different.

I’m glad you admit error. This is basic stuff.

> But the error is subtle, and no one has explained the discrepancy.
>
> THINK:
> The rock travels in a circular trajectory, around the ground point
> of the rope.
> It is driven by a centripetal force, always perpendicular
> to its velocity.
> It moves at constant speed.
> It moves with constant angular acceleration.

No, the angular acceleration is zero. Constant tangential speed means zero
angular acceleration. The centripetal acceleration is nonzero of course,
because the centripetal force is unbalanced.

>
> AND:
> The satellite travels in a circular trajectory, around the earth center.
> It is driven by a centripetal force - gravity - always perpendicular
> to its velocity.
> It moves at constant speed.
> It moves with constant angular acceleration.

No, the angular acceleration is zero. Constant tangential speed means zero
angular acceleration. The centripetal acceleration is nonzero of course,
because the centripetal force is unbalanced.

>
> Finally:
> There is tension in the rope, which transmits the force to the rock,
> which experiences internal stresses (the centrifugal force, loosely
> speaking), hence strain, in the direction along the rope.

It isn’t centrifugal force, even loosely speaking. It’s the centripetal
force exerted by the rope.

> The strain is measurable, in principle.
>
> Then, why is there no such centrifugal force felt by the satellite?

We do not feel gravity. We feel pressures on our body from material
surfaces, like from the floor.

Again, this is all basic stuff.

To understand relativity, you first have to learn basic stuff.

>
> Waving your hands and shouting "They're very different!" is mere
> hand waving. Asserting a fact does not explain the fact.
>
> There is an explanation. A challenge to the student: can you offer one?
>
> PS Your claim that this has been tested is silly.
>
> --
> Rich
>

--
Odd Bodkin -- maker of fine toys, tools, tables

On Thursday, October 14, 2021 at 6:51:42 PM UTC-7, RichD wrote:
> According to Newton, an orbiting body feels a centrifugal
> force from gravity, like a bola, a rock on a rope. This
> is a striking difference from general relativity, where a
> body in free fall is inertial.
>
> To my knowledge, this property has never been tested.
> But it must apply to satellites in orbit around earth.
> Could an experiment be performed on the space station
> to test this prediction? Or is the effect too small to detect
> with current technology?
>
> --
> Rich

Actually the fugal and petal have that the centri-fugal,
which is used to explain that swinging the bucket has
its weight on the axle besides that gravity keeps it,
that the tension on the rope basically establishes the
centrifugal frame as what holds the bucket "up" in its
new frame rotating with the angular: it's derived or
built up instead that's centri-petal force not centri-fugal,
that the usually derivation builds the centripetal not
the centrifugal, because, the centrifugal is in the potential
moment, while, the centripetal is in the what's also
used to compute the usual gravitational frame.

Then, the notion is that the "gravific" is the true centrifugal,
that for the gravitic and action over potential or "real action",
that the gravific is "real potential" and that also the centrifugal
is real potential while the usual centrifugal is a correct adjective
in the usual centripetal, that for the angular moment it's the terms,
basically for that gravity is gravific and the centripetal is centrifugal.

(Or where it is.)

Local boosts and the invariant make for that: field theory:
admits large standing waves.

Which is real potential action.

Remember that acceleration is smooth while at the same
time turns are abrupt, or vice versa and for stopping or
straightening, what results classical rest is classical motion.

So, "according to Newton, ... [for example], an orbiting body feels a
centripetal force, that according to Fatio/LeSage [for example] an
orbiting body feels a centrifugal force".

On Friday, October 15, 2021 at 2:22:53 AM UTC-7, Dirk Van de moortel wrote:
> Op 15-okt.-2021 om 03:51 schreef RichD:
> > According to Newton, an orbiting body feels a centrifugal
> > force from gravity, like a bola, a rock on a rope. This
> > is a striking difference from general relativity, where a
> > body in free fall is inertial.
> >
> > To my knowledge, this property has never been tested.
> > But it must apply to satellites in orbit around earth.
> > Could an experiment be performed on the space station
> > to test this prediction? Or is the effect too small to detect
> > with current technology?
> >
> > --
> > Rich
> >
> Think about this.
> According to Newton, an orbiting object does not
> "feel a centrifugal force from gravitity." It feels
> nothing. That has been tested.
> A satellite in orbit (aka free fall) is not on a rope.
> If you would attach a rope to an already circularly
> orbiting satellite, there would be no tension in that
> rope.
> With a rope you could imagine making it go "faster",
> there *would* be a tension in the rope, and the
> satellite would be no longer in free fall.
> A rock on a rope is not in orbit around your hand.
>
> Dirk Vdm

Any acceleration is that as though the force vector at
the instant is between them, each the centers of moments,
any acceleration is free in its own center what results though
that orbits are usually in larger orbits, whether an object
usually orbits by itself or spherically or together or planarly.

I.e., where the "speed of gravity" is the limit, just because the
local moment is free to displace its center, or leave it, that
the displacement would reconstitute itself an orbit while
the leaving would escape, still there that where the system
itself is also in a planar orbit, it's more likely to de-orbit back
from that it enters or leaves planar orbit for spherical orbit.

The speed of gravity is usually the limit.

Op 17-okt.-2021 om 17:21 schreef Ross A. Finlayson:
> On Friday, October 15, 2021 at 2:22:53 AM UTC-7, Dirk Van de moortel wrote:
>> Op 15-okt.-2021 om 03:51 schreef RichD:
>>> According to Newton, an orbiting body feels a centrifugal
>>> force from gravity, like a bola, a rock on a rope. This
>>> is a striking difference from general relativity, where a
>>> body in free fall is inertial.
>>>
>>> To my knowledge, this property has never been tested.
>>> But it must apply to satellites in orbit around earth.
>>> Could an experiment be performed on the space station
>>> to test this prediction? Or is the effect too small to detect
>>> with current technology?
>>>
>>> --
>>> Rich
>>>
>> Think about this.
>> According to Newton, an orbiting object does not
>> "feel a centrifugal force from gravitity." It feels
>> nothing. That has been tested.
>> A satellite in orbit (aka free fall) is not on a rope.
>> If you would attach a rope to an already circularly
>> orbiting satellite, there would be no tension in that
>> rope.
>> With a rope you could imagine making it go "faster",
>> there *would* be a tension in the rope, and the
>> satellite would be no longer in free fall.
>> A rock on a rope is not in orbit around your hand.
>>
>> Dirk Vdm
>
> Any acceleration is that as though the force vector at
> the instant is between them, each the centers of moments,
> any acceleration is free in its own center what results though
> that orbits are usually in larger orbits, whether an object
> usually orbits by itself or spherically or together or planarly.
>
> I.e., where the "speed of gravity" is the limit, just because the
> local moment is free to displace its center, or leave it, that
> the displacement would reconstitute itself an orbit while
> the leaving would escape, still there that where the system
> itself is also in a planar orbit, it's more likely to de-orbit back
> from that it enters or leaves planar orbit for spherical orbit.
>
>
> The speed of gravity is usually the limit.
>

"Basically", you should have stayed at sci.math, fumbling and
ranting about the cardinality of the even numbers.

Dirk vdm

On Sunday, October 17, 2021 at 10:40:13 AM UTC-7, Dirk Van de moortel wrote:
> Op 17-okt.-2021 om 17:21 schreef Ross A. Finlayson:
> > On Friday, October 15, 2021 at 2:22:53 AM UTC-7, Dirk Van de moortel wrote:
> >> Op 15-okt.-2021 om 03:51 schreef RichD:
> >>> According to Newton, an orbiting body feels a centrifugal
> >>> force from gravity, like a bola, a rock on a rope. This
> >>> is a striking difference from general relativity, where a
> >>> body in free fall is inertial.
> >>>
> >>> To my knowledge, this property has never been tested.
> >>> But it must apply to satellites in orbit around earth.
> >>> Could an experiment be performed on the space station
> >>> to test this prediction? Or is the effect too small to detect
> >>> with current technology?
> >>>
> >>> --
> >>> Rich
> >>>
> >> Think about this.
> >> According to Newton, an orbiting object does not
> >> "feel a centrifugal force from gravitity." It feels
> >> nothing. That has been tested.
> >> A satellite in orbit (aka free fall) is not on a rope.
> >> If you would attach a rope to an already circularly
> >> orbiting satellite, there would be no tension in that
> >> rope.
> >> With a rope you could imagine making it go "faster",
> >> there *would* be a tension in the rope, and the
> >> satellite would be no longer in free fall.
> >> A rock on a rope is not in orbit around your hand.
> >>
> >> Dirk Vdm
> >
> > Any acceleration is that as though the force vector at
> > the instant is between them, each the centers of moments,
> > any acceleration is free in its own center what results though
> > that orbits are usually in larger orbits, whether an object
> > usually orbits by itself or spherically or together or planarly.
> >
> > I.e., where the "speed of gravity" is the limit, just because the
> > local moment is free to displace its center, or leave it, that
> > the displacement would reconstitute itself an orbit while
> > the leaving would escape, still there that where the system
> > itself is also in a planar orbit, it's more likely to de-orbit back
> > from that it enters or leaves planar orbit for spherical orbit.
> >
> >
> > The speed of gravity is usually the limit.
> >
> "Basically", you should have stayed at sci.math, fumbling and
> ranting about the cardinality of the even numbers.
>
> Dirk vdm

Somebody had to do it....

Thank you though for your initial kindness.

(As if you don't know the argument about uncountability and
the Cantorian is about as cranky in mathematics as the argument
about relativity and the Einsteinian is in physics, i.e., it's usually
the hopelessly all-the-way-cranky. So, arguing for the absolute
usually eg the total field or domain principle, without visiting the
entire edifice of the relativistic and transfinite hierarchy or at least
overall its parts, is more than less hopelessly cranky or crankish,
though for foundations, while any plank of belief of course is
itself a theoretical edifice. Also the retro-fixed or retro-finite are
not the same as retro-total or retro-absolute, what the theory includes.)

Then the difference between centrifugal and centripetal about
what formulas are used to write the each, and that they point
to each other and together, "the" force vectors of each with respect
to the other the potential or action, here is for the inertial moment
as angular, because no two centers ever collide exactly.

Ah, then if you'll excuse me, or won't, please let's relate acceleration
usually as there are the terms from rest to velocity, and, the terms
from velocity to rest, either of which are acceleration with respect
to v = 0 or v = 1. These are differential terms though what with
respect to that angular rotation is either spinning the hub or the
hub, spinning.

The turning Earth has anti weight.
Rotation came from formation of the Earth.
The angular momentum speed is not
a force weight but a weight from turning motion..
There is force weight then motion weight.

Mitchell Raemsch

On 10/14/21 8:51 PM, RichD wrote:
> According to Newton, an orbiting body feels a centrifugal
> force from gravity, like a bola, a rock on a rope.

Newton said no such thing. Neither does Newtonian mechanics (including
gravitation).

In Newtonian mechanics, F=ma applies in an inertial frame. There's no
"centrifugal force" there in any way, shape, or form, for any sort of
motion (including orbiting satellites and bolas).

[Ditto for "Coriolis force", and the less well known
"Euler force" in a non-uniformly-rotating system.]

If you analyze a rock on a rope circulated by hand, using an inertial
frame, there is no "centrifugal force", and the tension in the rope is
simply the centripetal force causing the rock to move in a circle. If
you analyze a satellite using the locally inertial frame in which the
earth is at rest, there is similarly no "centrifugal force", and the
centripetal force is that of gravity.

In a ROTATING system, in order to apply F=ma one must IMAGINE a
fictitious "centrifugal force" -- it is not a real force and actually
accounts for the non-inertial, rotating coordinates used.

Note it is IMPOSSIBLE to measure "centrifugal force" [#]. One can
calculate its effect in any system of rotating coordinates, but there is
no way to connect up a spring scale (or equivalent) to measure it.

[The kicker is: there is no way to measure gravitational
force, either, and for the same reason -- there is no
place to connect up a spring scale (or equivalent) to
measure it. That is, at base, why GR can do without
"gravitational force" and model gravity as curvature
of spacetime.]

[#] Nor can one feel "centrifugal force" -- humans
can only feel real forces, such as the pull from a
seat belt on a person's right side when the car
turns rapidly to the left. We cannot feel the force
of gravity, we only feel the upward push from floor
or chair.

> This
> is a striking difference from general relativity, where a
> body in free fall is inertial.

The non-existent "centrifugal force" is not the difference, the
difference actually is modeling gravitation as a force (Newton) or as
the curvature of space-time (GR).

> To my knowledge, this property has never been tested.

Then you are extraordinarily ignorant about very basic physics, and its
history. The "centrifugal and Coriolis forces" were invented to explain
the behavior of long-range artillery on the surface of the (rotating)
earth. They have been tested literally zillions of times -- so much so
that such tests are no longer interesting or published.

> But it must apply to satellites in orbit around earth.

Certainly, IF ONE USES A ROTATING SYSTEM TO MODEL THEM. If one uses
inertial coordinates, there is no "centrifugal force" and the issue
simply never comes up. For a satellite, nobody in their right mind would
use rotating coordinates.

> Could an experiment be performed on the space station
> to test this prediction? Or is the effect too small to detect
> with current technology?

As I said before, this has been tested zillions of times; the ISS is not
at all an appropriate venue for such tests.

> why is there no such centrifugal force felt by the satellite?

Because "centrifugal force" is not real, it is only a mathematical
artifice for using rotating coordinates in Newtonian mechanics.

> Waving your hands and shouting "They're very different!" is mere
> hand waving. Asserting a fact does not explain the fact.

The fact is that "centrifugal force" is an artifact of using rotating
coordinates; the consequence is that it is neither real nor subject to
feeling by humans, because neither nature nor human sense organs use any
coordinates at all. This is not mere "hand waving", this is what these
words mean and how they relate to each other.

Tom Roberts

Circular motion is not a force of its own.
It creates weight from its speed not
by being a force...

Mitchell Raemsch

On October 17, tjrob137 wrote:
>> According to Newton, an orbiting body feels a centrifugal
>> force from gravity, like a bola, a rock on a rope.

This is admittedly erroneous.
The question is, what makes it so?
You miss the point by a mile. Instead, you run off on canned
Physics 101 lectures.

[snip lecture on centrifugal force fallacy]

Yes yes, a million physics students have been told "There's no such thing!"
I use 'centrifugal force' deliberately, because it's colloquial, I talk plain English.

A billion chinese don't know what's a centripetal force, but they do
understand a centrifuge. Centrifuge, centrifugal, get it?

> If you analyze a rock on a rope circulated by hand, using an inertial
> frame, ... the tension in the rope is simply the centripetal force causing
> the rock to move in a circle. If you analyze a satellite using the locally
> inertial frame in which the earth is at rest, ... and the centripetal force is that of gravity.

Bravo.
In both cases, orbital motion results from a constant centripetal force,
the so-called 'central force'.
This is the crux of the biscuit.

[snip rambling on Coriolis and rotating coordinates]
> [The kicker is: there is no way to measure gravitational
> force, either, and for the same reason -- there is no
> place to connect up a spring scale to measure it. That is,
> at base, why GR can do without "gravitational force" and model
> gravity as curvature of spacetime.]
> [#] Nor can one feel "centrifugal force" -- humans
> can only feel real forces, such as the pull from a
> seat belt on a person's right side when the car
> turns rapidly to the left. We cannot feel the force
> of gravity, we only feel the upward push from floor
> or chair.
>
> The fact is that "centrifugal force" is an artifact of using rotating
> coordinates; the consequence is that it is neither real nor subject to
> feeling by humans, because neither nature nor human sense organs use any
> coordinates at all.

Centrifuges don't work, they're illusions.
OK

Amidst your stream of consciousness, you somehow overlooked
the equivalence of inertial and gravitational mass.

Thus, for the simplest case - a body falling straight to earth center -
one doesn't feel any applied force, they cancel. A spring gauge
doesn't respond.

But the question here concerns orbiting bodies, circular motion. The
rock on a bola (or spokes on a wheel) feels stress, due to centrifugal
force. A satellite feels no such internal stresses. Yet both follow the
same trajectory, resulting from a constant centripetal force.

How to explain the difference?
The equivalence principle is part of the answer, but incomplete.

This is amusing. It started with a misconception, but has evolved into
a conundrum which no one can handle, although it's schoolboy level.

--
Rich

On October 17, bodk...@gmail.com wrote:
>>>> According to Newton, an orbiting body feels a centrifugal
>>>> force from gravity, like a bola, a rock on a rope. This
>>>> is a striking difference from general relativity, where a
>>>> body in free fall is inertial.
>>>> But it must apply to satellites in orbit around earth.
>>>> Could an experiment be performed on the space station
>>>> to test this prediction?
>
>>> According to Newton, an orbiting object does not
>>> "feel a centrifugal force from gravitity." It feels nothing.
>>> A satellite in orbit (aka free fall) is not on a rope.
>>> A rock on a rope is not in orbit around your hand.
>
>> The origin of this idea stems from describing Newtonian gravity
>> as a central force (on the planets, typically). The physics of a bola
>> is described the same way. It's misleading, to say the least.
>> On second and third thought, I admit error here. They are different.
>> But the error is subtle, and no one has explained the discrepancy.
>
>> The rock travels in a circular trajectory, around the ground point
>> of the rope.
>> It is driven by a centripetal force, always perpendicular
>> to its velocity.
>> It moves at constant speed.
>> It moves with constant angular acceleration.
>
> No, the angular acceleration is zero.

oops, typo.
constant angular velocity, etc.

>> AND:
>> The satellite travels in a circular trajectory, around the earth center.
>> It is driven by a centripetal force - gravity - always perpendicular
>> to its velocity.
>> Then, why is there no such centrifugal force felt by the satellite?
>
> We do not feel gravity. We feel pressures on our body from material
> surfaces, like from the floor.
> To understand relativity, you first have to learn basic stuff.

Recap the dialogue so far:
"What is the difference between a whirling rock on a rope, vs. a satellite,
both driven by a centrally directed centripetal force, where one experiences
a strain, while the other doesn't?"
"Because in an elevator, you feel pressure on the soles of your feet!"

Thank you for playing our game.

There is a BASIC explanation, of substance, which obviously eludes you.
You might ask, and learn something. But apparently, you'd rather
spout off about learning the basics.

--
Rich

On Monday, October 18, 2021 at 5:34:02 PM UTC-7, RichD wrote:
> On October 17, bodk...@gmail.com wrote:
> >>>> According to Newton, an orbiting body feels a centrifugal

> Rich

Off topic

RichD <r_delaney2001@yahoo.com> wrote:
> On October 17, tjrob137 wrote:
>>> According to Newton, an orbiting body feels a centrifugal
>>> force from gravity, like a bola, a rock on a rope.
>
> This is admittedly erroneous.
> The question is, what makes it so?
> You miss the point by a mile. Instead, you run off on canned
> Physics 101 lectures.
>
> [snip lecture on centrifugal force fallacy]
>
> Yes yes, a million physics students have been told "There's no such thing!"
> I use 'centrifugal force' deliberately, because it's colloquial, I talk plain English.
>
> A billion chinese don't know what's a centripetal force, but they do
> understand a centrifuge. Centrifuge, centrifugal, get it?

Yes, see that’s the problem with “plain English”. There’s a lot of baggage
and assumptions and vagueness that threads through plain English. This is
why learning the subject from the beginning helps with the precise meanings
of physics terms as used in physics.

>
>> If you analyze a rock on a rope circulated by hand, using an inertial
>> frame, ... the tension in the rope is simply the centripetal force causing
>> the rock to move in a circle. If you analyze a satellite using the locally
>> inertial frame in which the earth is at rest, ... and the centripetal
>> force is that of gravity.
>
> Bravo.
> In both cases, orbital motion results from a constant centripetal force,
> the so-called 'central force'.
> This is the crux of the biscuit.
>
> [snip rambling on Coriolis and rotating coordinates]
>
>> [The kicker is: there is no way to measure gravitational
>> force, either, and for the same reason -- there is no
>> place to connect up a spring scale to measure it. That is,
>> at base, why GR can do without "gravitational force" and model
>> gravity as curvature of spacetime.]
>> [#] Nor can one feel "centrifugal force" -- humans
>> can only feel real forces, such as the pull from a
>> seat belt on a person's right side when the car
>> turns rapidly to the left. We cannot feel the force
>> of gravity, we only feel the upward push from floor
>> or chair.
>>
>> The fact is that "centrifugal force" is an artifact of using rotating
>> coordinates; the consequence is that it is neither real nor subject to
>> feeling by humans, because neither nature nor human sense organs use any
>> coordinates at all.
>
> Centrifuges don't work, they're illusions.
> OK

Sure they work. They just don’t work with centrifugal force, no matter how
lay people describe their operations. If what’s in the centrifuge is a
fluid, for example, the active force is a pressure differential in the
fluid, sometimes called a buoyancy force, and that is centripetal, not
centrifugal. It’s only the sloppy “plain English” that describes poorly how
centrifuges work.

>
> Amidst your stream of consciousness, you somehow overlooked
> the equivalence of inertial and gravitational mass.
>
> Thus, for the simplest case - a body falling straight to earth center -
> one doesn't feel any applied force, they cancel. A spring gauge
> doesn't respond.
>
> But the question here concerns orbiting bodies, circular motion. The
> rock on a bola (or spokes on a wheel) feels stress, due to centrifugal
> force. A satellite feels no such internal stresses. Yet both follow the
> same trajectory, resulting from a constant centripetal force.
>
> How to explain the difference?
> The equivalence principle is part of the answer, but incomplete.
>
> This is amusing. It started with a misconception, but has evolved into
> a conundrum which no one can handle, although it's schoolboy level.
>
> --
> Rich
>

--
Odd Bodkin -- maker of fine toys, tools, tables

Round motion creates weight.
Gyro and centrifuge rotation speed
is creating outward weight.
They do not have a force for
them selves along...
Weight is made by force and also
motion.

Mitchell Raemsch

On 10/18/21 7:31 PM, RichD wrote:
> [... to me] Amidst your stream of consciousness, you somehow
> overlooked the equivalence of inertial and gravitational mass.

I did not "overlook" it, because it is irrelevant to the discussion.
Nowhere do I use that equivalence.

Note: The context here is Newtonian mechanics (NM).

> Thus, for the simplest case - a body falling straight to earth
> center - one doesn't feel any applied force, they cancel.

For the case you describe, there is just ONE force on the falling body,
that of gravity. What "they" do you think "cancel"????

In fact, in NM, one uses an earth-fixed set of coordinates, and relative
to them the falling body accelerates: F=ma applies.

A human in freefall, neglecting air, does not feel any force, for the
simple reason that there is no strain on any part of the body, and our
ability to feel forces is really due to internal strains in our bodies
(the sensory nerves get stretched and report this to the brain).

> A spring gauge doesn't respond.

WHERE would you connect a spring gauge to a body in freefall????

If you connect it between a support and the body, then that body is no
longer in freefall, and the spring gauge measures its own force of
tension supporting the body -- it DOES NOT measure the gravitational
force (though under the right circumstances it measures a force equal
and opposite to the gravitational force on the body).

> But the question here concerns orbiting bodies, circular motion.

OK. So why do you immediately turn to a quite different situation? I'll
follow your lead and do so, too.

> The rock on a bola (or spokes on a wheel) feels stress, due to
> centrifugal force.

No. You are confused.
1) This is not stress, it is strain.
2) This is not due to "centrifugal force", it is simply due to
the force of tension in the rope, which diverts the rock from
its straight-line inertial path; F=ma in the inertial frame of
the center.
3) The rock feels strain because the rope is connected to a specific
part of the rock, and the pull must be distributed internally
throughout the rock via strains. This has nothing whatsoever to
do with "centrifugal force", but rather with how the rope is
attached to the rock; it applies to any pull on the rope connected
to the rock (not just circular motion).

If you analyze the rock in the rotating coordinates in which it is at
rest, then you need to account for it being at rest while the tension of
the rope is pulling on it -- THAT requires you to imagine a "centrifugal
force", wholly determined by the rotating coordinates, that balances the
tension force on the rock and leaves the rock unaccelerated and motionless.

But in the inertial frame of the center, the rock is obviously not at
rest, and not unaccelerated -- one does not need the "centrifugal force"
-- if you attempt to apply it you will get the wrong answer.

> A satellite feels no such internal stresses. Yet both follow the
> same trajectory, resulting from a constant centripetal force.

These are strains, not stresses.

The rock has internal strains due to the fact that the rope is connected
to a specific part of itself, so the pull has to be distributed
internally throughout the rock, via strains. The satellite has no
internal strains due to the fact that the gravitational force keeping it
in its orbit is "connected" to every infinitesimal part of its body;
there is no need to distribute the force via internal strains.

> How to explain the difference?

I just did.

> The equivalence principle is part of the answer, but incomplete.

Not in NM. Nowhere above did I need the EP.

> This is amusing. It started with a misconception, but has evolved
> into a conundrum which no one can handle, although it's schoolboy
> level.

You are acting like an idiot here -- your personal limitations and
inabilities need not apply to everyone. Any physicist can "handle" this
just fine.

Tom Roberts

Rotation is motion creating weight...
not a force...

On October 21, tjrob137 wrote:
>> But the question here concerns orbiting bodies, circular motion.
>> The rock on a bola (or spokes on a wheel) feels stress, due to
>> centrifugal force.
>
> No. You are confused.
> 1) This is not stress, it is strain.
> 2) This is not due to "centrifugal force", it is simply due to
> the force of tension in the rope, which diverts the rock from
> its straight-line inertial path; F=ma in the inertial frame of
> the center.

You're too literal.

> 3) The rock feels strain because the rope is connected to a specific
> part of the rock, and the pull must be distributed internally
> throughout the rock via strains. This has nothing whatsoever to
> do with "centrifugal force", but rather with how the rope is
> attached to the rock; it applies to any pull on the rope connected
> to the rock (not just circular motion).

This is elementary, and nobody is confused on this point.

>> A satellite feels no such internal stresses. Yet both follow the
>> same trajectory, resulting from a constant centripetal force.
>
> The rock has internal strains due to the fact that the rope is connected
> to a specific part of itself, so the pull has to be distributed
> internally throughout the rock, via strains.
> The satellite has no internal strains due to the fact that the gravitational force
> keeping it in its orbit is "connected" to every infinitesimal part of its body;
> there is no need to distribute the force via internal strains.

Finally. That's the answer I looked for.

My point is, the textbooks are misleading. They paint a picture of gravity emanating
from earth center like a rope, swinging the moon around. Then the student infers a
centrifugal force, internally to the moon.

Of course the correct picture is the G field, acting at every point in space. Every
atom in the moon responds to that force, separately and independently. Carrying
this logic to its extreme, the moon is no longer a single object, but every atom is
an independent satellite of earth.

This is a strange way to think, but pedagogically, it's worthwhile.

--
Rich

On October 21, tjrob137 wrote:
> In fact, in NM, one uses an earth-fixed set of coordinates, and relative
> to them the falling body accelerates: F=ma applies.
> A human in freefall, neglecting air, does not feel any force, for the
> simple reason that there is no strain on any part of the body, and our
> ability to feel forces is really due to internal strains in our bodies
>
>> A spring gauge doesn't respond.
>
> WHERE would you connect a spring gauge to a body in freefall????
> If you connect it between a support and the body, then that body is no
> longer in freefall, and the spring gauge measures its own force of
> tension supporting the body -- it DOES NOT measure the gravitational
> force.

Another thought -

The debate concerns extended bodies; a rope attaches to one point on the
load, the force transmits through the bulk, which then strains.

What about a point particle? In free fall, it doesn't feel 'the force of gravity'
(also true for an extended body).

But what about other forces? No length, no stress, no strain. A point particle
doesn't feel a force, never knows it's accelerating?

e.g. an electron in a vacuum, gets popped by an EM wave. It accelerates
(relative to an external frame) and radiates energy. It has rest mass and inertia.
It doesn't feel anything? It has no clue it's radiating?

This question never occurred to me before.

--
Rich