[Halc]

Anyway, point being, on the earth's surface you don't get the swimming up and down a river effect, so Michelson's experiment would not show earth rotation effects on light, but would it show effects from earth's orbit around the sun?

It was designed to detect motion relative to the medium (aether) in any direction. If there was such a medium and the current Newtonian model was accurate, all orbits, spins, etc would involve daily and annual variations due to changes from spin and orbit. The instrument was sufficiently sensitive to detect 1500 mph changes, which is the typical change in velocity over the course of 12 hours.
The experiment measured isotropy in all frames, which resolved the conflict between Newton's equations and Maxwell's equation. They couldn't both be right. Newton's model had been falsified.

So Michelson did prove a lack of aether but not a lack of Sagnac effect from earth's rotation.

Yet again, no proof of lack of aether was made. It was simply demonstrated to be superfuous. No test for Sagnac was made since the experiment didn't involve a loop enclosing an area.

Apparently you agree that said Sagnac effect exists

It had better. There are devices in use every day that depend on it.

but you explain it as a relativity consistent effect because it involves a rotating frame.

One can explain any situation using one's choice of frame. Sagnac is no exception, and can be explained via the properties of rotating frames, or it can be explained using only an inertial frame.

It doesn't actually confirm relativity

Relativity has little to say about the Sagnac effec that Newtonian physics didn't already explain. Unless the device is rotated at relativistic speeds, there's no need to invoke relativity theory to predict the Sagnac effect, so no, it isn't really a test of relativity since relativity doesn't predict anything different.

Einstein just gave himself an out by saying that rotating frames are not inertial.

Newton said that actually. He demonstrated that rotation is absolute, while linear velocity is not necessarily so (per Galileo).

Now there's the conundrum of why a rotating frame can be confirmed to be in rotation like that, what is it in rotation relative to?

No relation needed in the case of rotation. That's what it means to say rotation is absolute. The rate of rotation of a closed system can be determined from within a box.

The same would apply to binary stars in orbit with each other, what are they rotating in relation to? Presumably an imaginary point between them called the barycenter, but how is the barycenter a stationary reference? It seems counter to relativity theory.

Well, for a closed system, there is a frame independent worldline for the center of gravity of the system which does not accelerate, so is stationary in the frame of the system. The word 'barycenter' only applies to two-body system since with more bodies, nothing necessarily moves in a predictable path about the center of gravity, nor is even particularly attracted in its direction.
Picture a rock in space, not rotating. It has zero angular momentum relative to its center of gravity, and for that matter, relative to any point in space in the frame where that rock is stationary. But in a frame where the rock is moving, the rock has angular momentum relative to any point in space that is not on the line of its motion. So in that sense, angular energy and momentum about random points in space are frame dependent.

If there are two equal disks with the same axis, with a space between the two, what is the difference between one being stationary and the other rotating and the other way around, or both rotating in opposite directions at equal angular velocity?

The first system has nonzero angular momentum. The 2nd system has zero angular momentum. Remember that momentum, like velocity, is a vector, and one must use vector addition when adding up the momentums of the respective parts.

To illustrate this, you can have a small box with two disks in it spinning on an axis fixed to the box. In the first case, the box has angular momentum and if you hold it, you'll notice a resistance to turning it due to gyroscopic effects. In the second case with the disks spinning in opposite directions, the box has zero angular momentum and will not resist being turned this way and that. There would be an effortless test to determine which case is which, without having to look inside the box.

Another test: if you're on the ring of a windowless space station rotating for gravity, you can tell the direction of rotation by peeing in a bucket and seeing which way the stream curves. Even light bends to the side due to Coriolis forces.

The only difference between the two disk frames is that an observer on one would perceive centrifugal force and one on the other would not.

There you go. It's not the only difference, but it's the most obvious. You could do really subtle special relativity stuff like measure the diameter and circumference of the disk, which will have a ratio of π only for a non-rotating disk, but to get a measurable difference with say just a tape measure, you'd have to spin it at a rate which would kill a human.

The use of energy to create force to produce rotational motion in one.

Force (torque actually) is only needed to change the angular momentum of the thing. No torque is needed to keep it spinning, per Newton's laws.

Kinetic energy had been stored in the disk as inertial motion. The disk would continue to rotate, assuming no external friction or resistance, until that kinetic energy was transferred to another mass by exerting a force moving it outward from a position close to the axis to one farther away from it.

To move mass inward, energy needs to be imparted to the system. The ice skater needs to perform work to pull her arms in and spin faster. Likewise, to move outward, excess energy must go somewhere. So for example, the spin of Earth momentum is slowly being transferred to the moon, raising its orbital radius. Of all the energy Earth loses in this process, only about 3% of it goes to the moon (a higher radius orbit is a higher energy orbit) and the excess is radiated away as heat.

We're getting pretty off topic here. OK, a lot of this is discussion of relations, and that's good. But very little of it differs between Einstein's physics and what came before. Newton may have been falsified for the boundary cases, but they very much still teach Newtonian physics in schools. It works just fine for most applications, and nobody needed to apply relativity theory to get a man on the moon.

[Origin]

It was designed to detect motion relative to the medium (aether) in any direction.

Excellent post, too bad Centra won't read it with an open mind, I have no doubt many of the members and guests will however.  I admire your patience with posters like Centra, keep up the good work.

[Centra (OP)]

That last post was actually somewhat informative, Halc, which is a nice change from the usual insulting. As a brief aside from relativity, something I find interesting involving rotation is that to equal earth's gravitational acceleration of 9.807 m/sē with rotation all that's required is a 10 m diameter and an angular velocity of 13.374 rpm. That's slow, over 4 seconds per rotation, you could easily achieve that by manually pushing it around. It seems like earth gravity is strong when you think of a boulder or something heavy like that but it's surprisingly weak if you look at it as the equivalent of centrifugal force.

[Centra (OP)]

It was designed to detect motion relative to the medium (aether) in any direction.

Excellent post, too bad Centra won't read it with an open mind, I have no doubt many of the members and guests will however.  I admire your patience with posters like Centra, keep up the good work.

Patience, are you kidding? He insults me regularly. You know, like you.

[Origin]

Patience, are you kidding? He insults me regularly. You know, like you.

This is a science site and your pseudoscience attitude is insulting.  It's also insulting to take time to help you understand a concept and have you ignore it.  Purposely or not you are trolling so don't be surprised to be treated like a troll.

[Centra (OP)]

Patience, are you kidding? He insults me regularly. You know, like you.

This is a science site and your pseudoscience attitude is insulting.  It's also insulting to take time to help you understand a concept and have you ignore it.  Purposely or not you are trolling so don't be surprised to be treated like a troll.

You too huh?

[Centra (OP)]

Here is a comment about the illusion of relative motion, which is in the same vein as the illusion of velocity, it shows how wrong assumptions can be made in the subject of relativity. I mentioned something about this earlier but I was thinking about again just now so thought I would write a new comment about it.

Seems to me that two objects of very different masses shouldn't really be considered interchangeable as to mutual motion. It's obvious that it would take 10 times as much energy or force to move a 10 kg object the same distance as a 1 kg object, so why should they be given equal relative motion? If they move apart 100 m then isn't it logical that the 10 kg object should be regarded as having moved 9.090909 m and the 1 kg object 90.90909 m? Granted the velocity between the two objects would be the same, but the relative share of the distance between the two objects would not. Two objects moving apart, regardless of how it came about, can be viewed as the two spaces between the barycenter and each object both increasing while maintaining the same ratio. I think Einstein overlooked that important concept.

 Now you might ask what if a planet and a rocket are involved? The planet's share off the distance would be practically nil in that case and couldn't even be calculated with accuracy. Such are the problems that can arise in working with relative motion, sometimes it's essentially a stationary frame and a moving one, the mismatch in mass is so extreme. The speed of light would be constant in relation to the center of mass, like the earth, not necessarily the surface thereof, if it's in rotation. Why? because it would have to be constant in relation to different levels of the surface, and even underground levels, all of which would be moving at different angular velocities, thus, light would have no one constant reference at all. Looking at light at sea level from the top of a mountain would present some simultaneity problems, even though there was seemingly only a single frame, the ground at sea level would not actually be in relative motion to the mountaintop and yet light would seem to move at different rates.

[Bored chemist]

so why should they be given equal relative motion?

Because it's exactly as far from A to B as it is from B to A.
So, when you write stuff like  this, and then say

Granted the velocity would be the same, but the relative motion would not.

It looks like you are trolling.
Because the time taken is the same, and the velocity is the same, but somehow, you think the distance (which you can calculate by multiplying the same velocity by the same time) is different.

Why don't you stop this nonsense?

[Centra (OP)]

so why should they be given equal relative motion?

Because it's exactly as far from A to B as it is from B to A.
So, when you write stuff like  this, and then say

Granted the velocity would be the same, but the relative motion would not.

It looks like you are trolling.
Because the time taken is the same, and the velocity is the same, but somehow, you think the distance (which you can calculate by multiplying the same velocity by the same time) is different.

Why don't you stop this nonsense?

Because the velocity is the time and distance between the two points but the relative motion is split at the barycenter into two sections, that's why. Now Why don't you stop this nonsense of critiquing things which are apparently beyond your level of comprehension?

[Bored chemist]

but the relative motion is split at the barycenter into two sections, that's why

Why?
Why not split it in the middle or, even better, why not decide that splitting it at all is pointless?

The reason why the distance between the two is not split is because there's no reason to.
Once you stop doing the pointless thing, it stops mattering how you might choose to do it.

Now Why don't you stop this nonsense of critiquing things which are apparently beyond your level of comprehension?

Everyone here apart from you agrees.
The whole of the world of physics agrees.
You are the only one who thinks you are right.
And it's clear  that you do not know what you are talking about.

So why are you trolling?

[Kryptid]

Because the velocity is the time and distance between the two points but the relative motion is split at the barycenter into two sections, that's why.

I'd like to see a source that supports this claim.

[Origin]

It's obvious that it would take 10 times as much energy or force to move a 10 kg object the same distance as a 1 kg object, so why should they be given equal relative motion? If they move apart 100 m then isn't it logical that the 10 kg object should be regarded as having moved 9.090909 m and the 1 kg object 90.90909 m?

No that would be absurd.  We are talking about relative velocity between objects.  It takes exactly the same amount of force to maintain the velocity of a 10 ton object as it does a 1 gram object.  They both require 0.0N to maintain their velocities.

[Centra (OP)]

Because the velocity is the time and distance between the two points but the relative motion is split at the barycenter into two sections, that's why.

I'd like to see a source that supports this claim.

Uh, you need a source for something which is obvious? You know a barycenter is a real thing, right? Well, if there were two unequal masses in outer space and a spring between them was released what do you think would happen? Would they both move an equal distance from the barycenter? Unless your answer is yes, no source is required, much like no source is required for me stating that the sky is blue, though for you, I guess i should specify when there are no clouds and it's noon. If you claim that the statement I just made is false then YOU are the one who would require a source, because then you're statement would be in contradiction to the established laws of physics, not mine. My source is the established laws of physics? Just Google "laws of physics". Do you want me to provide the URL for Google?

[Centra (OP)]

It's obvious that it would take 10 times as much energy or force to move a 10 kg object the same distance as a 1 kg object, so why should they be given equal relative motion? If they move apart 100 m then isn't it logical that the 10 kg object should be regarded as having moved 9.090909 m and the 1 kg object 90.90909 m?

No that would be absurd.  We are talking about relative velocity between objects.  It takes exactly the same amount of force to maintain the velocity of a 10 ton object as it does a 1 gram object.  They both require 0.0N to maintain their velocities.

No, YOU'RE talking about relative velocity between two objects, I'm talking about relative motion based on mass. Did the two objects start moving in opposite directions instantly and with equal velocity relative to the barycenter between them? What I stated is exactly what would happen if equal force was applied to both objects in opposite directions with no source of friction or resistance. By the time the distance between them was 100 m, the 10 kg one would be 9.090909 cm from their barycenter and the 1 kg object would be 90.90909 cm from it. Let's see you refute that.

[Centra (OP)]

People will say "but uniform motion does not involve accelerating so it would be equally interchangeable between objects of different mass". Maybe, but maybe not. To get to that uniform motion, one had more kinetic energy added to it than the other. A 10 kg mass moving away at 100 m/s from the same reference object that a 1 kg mass is also moving away from at the same velocity in the opposite direction has more stored kinetic energy than the 1 kg mass. Can objects of equal mass, one with no kinetic energy stored and the other with a certain amount stored be considered equally in motion relative to each other? I contend that they cannot, there is an asymmetry so how can they be considered equal?

 If there are two equal mass objects with rocket engines on them and rocket fuel is added to one and it fires the rocket until all fuel is consumed, both objects would then have equal mass but one would have the kinetic energy added by that fuel burn. Could you then say that both objects are identical because they are moving apart at the same relative velocity? There is clearly an asymmetry, one has momentum and kinetic energy and the other doesn't so they cannot be considered equal. The rocket that did not burn fuel could be considered to be moving away from the one that did at the same velocity but would it have momentum and kinetic energy? Logically it would not, it didn't do anything, it just sat there. Stored energy is a real thing, it can't just be disregarded, so the two objects cannot be considered equal, the one with stored kinetic energy is in motion, the other is not, even though they may appear equally in motion relative to each other.

[Bored chemist]

Uh, you need a source for something which is obvious?

It's only "obvious" to you.
The rest of us realise it's wrong or meaningless.

[Bored chemist]

Well, if there were two unequal masses in outer space and a spring between them was released what do you think would happen?

From the point of view of an ant standing on one of the masses, the other mass moves.
That's what relative means.

[Origin]

No, YOU'RE talking about relative velocity between two objects,

This thread is about velocity, but I guess you forgot.  Now you want to talk about acceleration.

I'm talking about relative motion based on mass.

Now you want to talk about velocity again.  Relative motion is not based on mass.

Did the two objects start moving in opposite directions instantly and with equal velocity relative to the barycenter between them?

It does not matter, one or both objects could have accelerated at any rate in the past it is immaterial.

What I stated is exactly what would happen if equal force was applied to both objects in opposite directions with no source of friction or resistance.

Now you want to talk about forces.  Yes a given force will accelerate different mass at different rates.  F=ma.

[Centra (OP)]

No, YOU'RE talking about relative velocity between two objects,

This thread is about velocity, but I guess you forgot.  Now you want to talk about acceleration.

I'm talking about relative motion based on mass.

Now you want to talk about velocity again.  Relative motion is not based on mass.

Did the two objects start moving in opposite directions instantly and with equal velocity relative to the barycenter between them?

It does not matter, one or both objects could have accelerated at any rate in the past it is immaterial.

What I stated is exactly what would happen if equal force was applied to both objects in opposite directions with no source of friction or resistance.

Now you want to talk about forces.  Yes a given force will accelerate different mass at different rates.  F=ma.

Oh I didn't realize I had to start a new thread for every word. Maybe I should have called it the Mass Velocity Force Rotation Motion Kinetic Energy Momentum Relativity Acceleration Gravity Light Theory. Would that make you happy?

[Origin]

People will say "but uniform motion does not involve accelerating so it would be equally interchangeable between objects of different mass". Maybe, but maybe not.

No maybes about it the answer is yes.

To get to that uniform motion, one had more kinetic energy added to it than the other.

False.

A 10 kg mass moving away at 100 m/s from the same reference object that a 1 kg mass is also moving away from at the same velocity in the opposite direction has more stored kinetic energy than the 1 kg mass.

From the frame of the reference object the 10 kg object would have the highest KE.  From the frame of the 10 kg object the 1 kg object would have the highest KE unless the reference object was much more massive in which case the reference object would have the highest KE, but you didn't specify the mass of the reference object so I can't say for sure.

Can objects of equal mass, one with no kinetic energy stored and the other with a certain amount stored be considered equally in motion relative to each other?

Yes they absolutely can.  Energy is frame dependent.  Let's name the objects of equal mass A and B.  From As frame it has no KE and object B has KE.  From Bs frame it has no KE and object A has KE.
By the way KE isn't "stored".

If there are two equal mass objects with rocket engines on them and rocket fuel is added to one and it fires the rocket until all fuel is consumed, both objects would then have equal mass but one would have the kinetic energy added by that fuel burn. Could you then say that both objects are identical because they are moving apart at the same relative velocity?

The rocket that had the fuel let's call A and the other we will call B.  Once As burn is over then you can say that from As frame it has no KE and that rocket B is moving away from it at some velocity and that it has KE.  From Bs frame it has no KE and A is moving away at some velocity and has KE.

The rocket that did not burn fuel could be considered to be moving away from the one that did at the same velocity but would it have momentum and kinetic energy?

Yes, absolutely from the frame of the rocket that did the burn.

Stored energy is a real thing, it can't just be disregarded, so the two objects cannot be considered equal, the one with stored kinetic energy is in motion, the other is not, even though they may appear equally in motion relative to each other.

There is no such thing as 'stored KE', KE is frame dependent.

You know Centra you could always learn some physics before you try to teach it!