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### Messages - spaceman spiff

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1
##### Flat Earth Theory / Re: Found a fully working flat earth model?
« on: June 08, 2022, 09:44:34 PM »
For the sake of clarity: Do you think the OP is suggesting they are showing us a Euclidean space FE in this thread?

Don't know if this was intended to me or not, but OP's model is not Euclidian

2
##### Flat Earth Theory / Re: Found a fully working flat earth model?
« on: June 06, 2022, 11:06:26 PM »
Could you point me to an example of a tensor that IS NOT INVARIANT under coordinate transformation?
I don't know how many times I need to say that coordinate transforms are completely irrelevant here, but I'll try once more. If you keep rambling about this, I'll just ignore you.

Tensors are invariant with coordinate transformations.
Assuming a Euclidean space, which this emphatically is not.

But all of this started by you qualifying a claim that tensors are invariant under coordinate transformations, saying it assumes Euclidian space. Now coordinate transformations are irrelevant. Perhaps if you don't mean invariant under coordinate transformations, invariant with respect to what?
If you ignore it, ok no problem. We all will carry on with our lives

3
##### Flat Earth Theory / Re: Found a fully working flat earth model?
« on: June 06, 2022, 09:58:54 PM »
Complexity is an FE tactic to make their idea possible by obscuring simple truth.
This is your twice-pagely reminder that OP is a RE'er and he's making fun of all of you. There are no "FE tactics" in place here. OP is a RE'er and he is presenting RET, unaltered. It is extremely disingenuous of you to take a RE troll and describe his jokes as "FE tactics".

This is incorrect, tensors are invariant under coordinate transformations in any space they are defined, Euclidian or not. Perhaps my post wasn't clear enough
Your post was quite clear, and my response stands. If you think repeating yourself for the fourth time will help, it will not.

[/b]Perhaps your confusion lies in the fact that it is possible to come up with a non-Euclidean space in which your assertion holds.[/b] I could have been more precise, but I wasn't - it wasn't particularly necessary given that the exact space we're discussing has been specified, and given that the incorrect assumptions about this space were also made clear.

My assertion: Tensors are invariant under coordinate transformations.

Perhaps then you could help me clear my confusion please, because I'm having trouble coming up with an example that is the exact opposite of the bolded part in your quote.
Could you point me to an example of a tensor that IS NOT INVARIANT under coordinate transformation? Everything I'm reading says that this is not possible since the definition of a tensor does not rely on any coordinate basis, confirming my assertion.

4
##### Flat Earth Theory / Re: Found a fully working flat earth model?
« on: June 06, 2022, 07:32:47 PM »
A true tensor is invariant under any coordinate transformation.
I said nothing about coordinate transformations, merely the assumptions required for this statement to hold. Restating the statement louder is not gonna help.

Its components in a give base may change when you change coordinates (and this happens whether in euclidian or non-euclidian spaces), but a tensor is not defined by its coordinates.
Correct, but also delightfully irrelevant.

You didn't say, but you quoted specifically a part of someone else's post mentioning tensors are invariant under coordinate transformations, stating that this assumes Euclidian space. This is incorrect, tensors are invariant under coordinate transformations in any space they are defined, Euclidian or not. Perhaps my post wasn't clear enough

5
##### Flat Earth Theory / Re: Found a fully working flat earth model?
« on: June 06, 2022, 01:56:51 PM »

Tensors are invariant with coordinate transformations.
Assuming a Euclidean space, which this emphatically is not.

This is incorrect. A true tensor is invariant under any coordinate transformation. A tensor is a multilinear map from vectors and dual vectors to real numbers and does not depend on a coordinate system to be defined. Its components in a give base may change when you change coordinates (and this happens whether in euclidian or non-euclidian spaces), but a tensor is not defined by its coordinates.

6
##### Flat Earth Theory / Re: Found a fully working flat earth model?
« on: February 25, 2022, 09:16:10 PM »
Quote from: troolon
You can have infinitely many distance metrics. You have to choose one that make sense and haversine seems to match reality.
Yes, but a flat surface, by definition, has an euclidian metric. That is, the euclidian metric gives the shortest distance between 2 points, not haversine.

Quote from: troolon
Intrinsically my model behaves like a globe. Extrinsically it's flat. When we look at a model, we look at it from the outside so extrinsically.
So i would argue it's possible to create a flat earth representation, that mathematically behaves just like a globe would.

There seems to be a bit of confusion here. Extrinsic curvature has a very precise definition: it's the curvature seen by embedding the surface in a higher dimensional manifold. In order to see the extrinsic curvature of a 3-sphere, you'd need to be in 4 spatial dimensions. We are not, therefore we cannot see the extrinsic curvature in reality. You could, if you embed your earth in R4, but that's a purely mathematical tool that has no correspondence in reality since we live in 3 spatial dimensions. So in this sense you could "look at the model from outside", with the caveat that this cannot be done in the real world. So if you claim that earth is flat in 4D space, whatever. It's untestable and unfalsifiable, specially because you said if behaves exactly like a globe in 3D space. Furthermore, for the inhabitants of this world, it would appear curved since the intrinsic curvature is not zero.

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- What does the earth look like in an orthonormal reference frame/euclidian geometry
This question is a bit strange. We have mentioned this before, but curvature does not care about coordinates. I don't understand how you can look at a surface in "euclidian geometry". Its properties are not dependent on the coordinate system you use. And by the way, a (lon,lat) system of coordinates on a sphere is also orthonormal, as are polar coordinates in a plane, cylindrical coordinates, ...

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- Can we model physics on a flat earth?
You have yet to show that since your model is not flat, unless in the sense described above.

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- What is the real shape of the planet / what is the correct coordinate system?
These questions are completely unrelated, and there's no correct coordinate system. You can choose whatever you want, but as we said before, the properties of the surface such as curvature are not coordinate dependent.

7
##### Flat Earth Theory / Re: Found a fully working flat earth model?
« on: February 23, 2022, 01:18:36 PM »
https://www.education.vic.gov.au/school/teachers/teachingresources/discipline/science/continuum/Pages/scimodels.aspx
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A scientific model is a physical and/or mathematical and/or conceptual representation of a system of ideas, events or processes. Scientists seek to identify and understand patterns in our world by drawing on their scientific knowledge to offer explanations that enable the patterns to be predicted. The models scientists create need to be consistent with our observations, inferences and current explanations. However, scientific models are not created to be factual statements about the world.

It's... not a model?

OP's model is a model of the round earth, agreed. But it's not a model of a flat earth according to the quote, since there's no current explanation for bendy light (or light behaviour in general).

8
##### Flat Earth Theory / Re: Found a fully working flat earth model?
« on: February 22, 2022, 07:28:16 PM »
Also, this is wrong. As it has been mentioned, curvature is invariant over a change of coordinates. If it's non-zero, there is no possible change of coordinates that can turn it to zero globally.
Doesn't matter the axis or coordinate basis. If your model has non-zero intrinsic curvature, it isn't flat
You're quite right the intrinsic curvature is indeed curved. Mathematically it's a curved space.
But i believe extrinsic curvature to be zero (i'm sure Rog will have a 70 page proof or something about this

When you look at a model of the world, you look at the model from the outside. So i believe it's correct to say it's a flat representation of physics.

For me personally i can even look at the world and experience it as the flat representation.
For example when i see a picture of a ship with a missing keel, i can very often imagine it's the light that's curving.
Or when i see a globe from space, i can superimpose the model and tell myself: ah yes, that's a flat disc distorted by curvy light.

Some people seem to feel more comfortable looking at the world as flat, and now science can explain the world in their view if they want to...

The extrinsic curvature is only defined when you embed a submanifold in a higher dimensional one. So for us it does not matter, since we can only experience 3 space dimensions; if the earth has zero extrinsic curvature for some beings that can experience 4D space, whatever. But even they will agree that for us mere 3D beings, earth is curved. So your model is curved (where it matters), not flat.

To the second part: of course you can assume earth is any shape you like and imagine light does whatever to conform to that. But then you're taking the shape as a premise, not conclusion. And "science" cannot explain a flat earth, since by definition it has to invoke yet unexplained physics, such as the behaviour of light. Which has never been seen to do what you want it for earth to be flat, and furthermore has no explanation at all beyond "light curves in the exact way for earth to be seen as a globe from space, for us to see sunsets and sunrises, for us to see objects with their bottom part obscured...". If you want to call this a "model" sure, but I think most of us expect a little more. And this is certainly not science

9
##### Flat Earth Theory / Re: Found a fully working flat earth model?
« on: February 17, 2022, 01:35:06 PM »
The really impressive thing is how patient OP has been in explaining it in 10 pages of posts.

He had me worried for a minute talking about teleporting, but it was just a lack of a better word to describe some of the artefacts in looking at things after the coordinate transformation in the model

At least from what I've seen, most of the pushback is coming from the fact that OP claimed to have found a "working flat earth model". And that it's impossible to know the shape of the earth, it could a disk, globe, cuboid, Klein bottle, etc. What he/she did was a simple coordinate transformation, and therefore the representation is still of a globe. The pictures he/she showed are not representing a flat surface, but a sphere. Then everything else is made to fit that particular representation

Quote from: troolon
A disc in an orthonormal basis, with orthonormal distances, will have a curvature of 0.
A disc in celestial coords, with spherical distances, will have the curvature of a sphere. (as shown)
Also, this is wrong. As it has been mentioned, curvature is invariant over a change of coordinates. If it's non-zero, there is no possible change of coordinates that can turn it to zero globally.

Quote from: troolon
The model has intrinsic curvature but noone says an orthonormal axis is the only way it can be viewed.
Doesn't matter the axis or coordinate basis. If your model has non-zero intrinsic curvature, it isn't flat

10
##### Flat Earth Theory / Re: Found a fully working flat earth model?
« on: February 10, 2022, 05:40:17 PM »
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And to finish it, if you calculate the curvature of your model to be different from 0, you don't have a flat earth. I hope this is clear
Only in an orthonormal reference frame. Shapes only make sense if you have defined a basis.

No, curvature does not depend on the choice of coordinates. You could define curvature without ever mentioning coordinates.

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We have presented two differently shaped models of the same physics.
They can't be differentiated by any test.
Therefore it's impossible to know the shape of the earth.
You don't have two different shapes. You said it yourself - take the globe, change coordinates, this is what you get. This cannot alter the "shape" you were using, no matter what coordinates you try to use. If your curvature was non-zero to start with, you can't make it zero (globally) just by a change in coordinate system.

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We now have 2 models: one with a flat earth, and one with a globe.
No, still only a globe represented differently than usual
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How do we know which one is correct? We device a test and check which model matches the results.
Only problem, both models are identical and always give the same result. There's no way to tell which one is right.
Ergo, we can't measure the true shape of the earth.
They give you the same result because they are the same model. Try to explain the sun/moon going below the horizon for an observer, but for others is still visible high in the sky. Or the fact that constellations keep their shape throughout the night, or the sun keeping the same size all day, or earth being seen as a globe from space. Of course you could chalk it up to "earth is flat, therefore some weird thing happens". But then you're not devising a test to know the shape, you're assuming the shape and then fitting everything else to that. Or, again, you invoke some handwavy-not-supported physics for that.
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As for inventing physics: please tell me why light travels straight in a globe world?
My guess is because it matches observations. Same thing with curvy light on a flat planet.
The two models are just one. The explanation remains the same.
Light travels straight provided there are no ways to refract, deflect or interact with light. We see they go straight (as in follow a geodesic) because this is what is observed and measured, no matter what the shape of the earth is. The sun is not the only source of light we have, you know. In this case, theory and experiment agree. However, bendy light on a flat earth is a complete ad hoc hypothesis, as it starts with the earth being flat and then it has to explain sunsets, sunrises, etc.
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Only if you're assuming an orthonormal basis. In an orthonormal basis Australia is broken.
The flat world i'm presenting has the equator and the NS-line as axis and coordinates are expressed in degrees (lat/long along these axis, just like a celestial coordinates)
I'm not assuming any basis. If the earth is flat, any map of it is a projection of a disk onto a smaller disk; no distortion happens. That means that if I measured the width of Australia to be 3000km (random number, doesn't matter for the argument) and 3000 pixels in a map, the scale is 1km/pixel everywhere. Therefore, measuring 3000 pixels anywhere else on the map means that distance is also 3000km.
And just to reiterate, distance is invariant by a change in coordinate system.

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How will you tell?
Both models are indistinguishable. You called them a single model.
There is no measurement or observation of reality that can tell them apart. They both represent is equally well.
They are a single model, and it was not me who said it, it was you. You took a globe earth, changed coordinates and projected it in a disk. Everything else was made to fit that disk based on the observations made on a globe earth.

11
##### Flat Earth Theory / Re: Found a fully working flat earth model?
« on: February 09, 2022, 03:21:15 PM »
I don't get what all the fuss is about, really, unless I've missed something.
Based on your reactin, you have probably totally understood.
From a physics viewpoint this model has nothing new to offer.
However in the context of the flat-earth-"debate", it offers a few interesting tidbits:
- There exists a working flat-earth model. People have been looking for this for over 100 years
- The true shape of the earth can never be known. It can be a globe, or flat or a pyramid. There's no way to measure it. It seems people do not always realize this.

But yes, you have probably understood everything correctly and your reaction is very typical for a physics graduate.

First bold quote contradicts what you said. You don't have a flat earth model, you have a globe earth model represented in a disk. A projection, nothing new. Then you make everything else fit to that shape, starting from a globe.

What people are trying to say is that reality gets in the way. If your model is meant to represent a truly, real, physical flat earth, there is absolutely no reason whatsoever for the scale of the map to be different depending on the location, and the distance metric should be euclidian everywhere. This clearly does not work, as you have mentioned about Australia.

On the second point, it can only be right if you disregard physics completely and only care about a purely mathematical model. The shape of sunlight, sunsets and sunrises, constellation retaining shapes throughout the night... all these are observations that point to a globe. You could MAKE them fit any projection of the earth you want, sure. But the instant you claim that any projection is actually reality, you'll need to invoke completely new and unsupported (by evidence) physics to explain the behaviour of light, the fact that people circumnavigate Antarctica, observations of earth from space, etc.

And to finish it, if you calculate the curvature of your model to be different from 0, you don't have a flat earth. I hope this is clear

12
##### Flat Earth Theory / Re: Found a fully working flat earth model?
« on: February 07, 2022, 01:27:27 AM »
I don't get what all the fuss is about, really, unless I've missed something.

Quote from: troolon
But as a general answer, my 3D model is globe physics, just rendered differently. If you take a globe, express it in in celestial coords (lat, long, distance), and then draw latitude on a straight instead of a radial axis, you'll get a flat-earth-universe. Physics works with celestial coords, and so it behaves like a globe, it just looks flat. So if a wave works on a globe, it also works on the flat renderering. The only difference is the shape of one axis.
The OP him/herself said that the model is globe earth rendered on a flat disk, with whatever it takes to make the shape of the sun's illumination match the observations, and calling the boundary of the disk a  "mathematical artefact".  It is not flat earth. The title of the thread is a bit disingenuous.

Saying that you can't differentiate between the models is also strange, since there aren't two models, but only one represented in different ways.

13
##### Flat Earth Investigations / Re: Fixed Planetary Mass and Dark Matter
« on: July 13, 2018, 03:25:41 AM »
You got it, DM has no efficient way of losing energy, that's why it's more diffuse. I still don't understand why the fixation with earth; if anything it would be attracted to the sun in the solar system, not the earth (or earth-moon). Besides that, there are millions of other stars way more massive than the sun. Given the collisionless nature of DM, it would most likely follow the denser regions. And models of structure formation predict that there are subhalos within the halo, exactly what you are saying. And we see that the distribution is not totally uniform. But, as we both agreed that DM is collisionless, the substructures formed are larger than that of ordinary matter.
The (possible) reason that there's more DM in the center it's because the halo was formed by gravitational collapse. It grew later on by mergers or pure accretion.
The same point works for the Sun too, added mass is even less likely there given it's primarily said to be composed of the lightest elements (and the only way to do away with that is to lose a gaseous Sun altogether, which RET can't do without a lot of revision) so there's no room to remove any as dark matter.
I agree dark matter would form larger haloes with this model, but it's when you get within that that there starts to be an issue. The dark matter that aggregated in areas that affect us, I don't agree that those haloes would be stable. You use the example of one collapsing at galactic center, but what about elsewhere? All the subhalos seem as though they should end up attracted to other massive bodies, and vice versa; for that to instead leave a gap with only one type of matter is headscratching. Sure, regular matter loses energy faster but that's a lot of time for their mutual gravitational pulls to not interact.
The milky way is composed mostly of dark matter. If anything, ordinary matter should follow, not the other way around. And it actually does, the density profiles for both baryonic and dark matter are similar (DM halo extends way beyond the visible disk for reasons we have already discussed).There's no gap anywhere, DM is present. It's just that the sun is at the outer edge of the galaxy and therefore the density is lower (for both kinds, compared to regions closer to the center).
If you accept that DM is collisionless and that it composes around 80 - 90% of galaxies, I don't see any way for it to concentrate around earth- (or even sun-) sized bodies, I would actually expect much larger substructures within the halo. And they are not static, they're moving around the center exactly like the solar system orbits the center of the galaxy.

14
##### Flat Earth Investigations / Re: Fixed Planetary Mass and Dark Matter
« on: July 12, 2018, 10:40:12 PM »

Dark matter has no limitations on its movement, I agree with that.
My issue still has to be with the effect of gravity on dark matter though. It would not need to form any actual structure, particularly if it collisionless. Take the RE moon and its orbit around the Earth's core; why not have dark matter do the same within the Earth? You could have tonnes of the stuff in the same location. That's a halo, the same structure you're talking about, just less diffuse.
The only reason I can see for it to be as diffuse as you've said is that it lacks an efficient way to lose energy, though they overlaps with the discussion I've had with ScienceThat; it needs to lose energy if it's to be present at all to affect the galaxy, especially galactic center.
I may be misunderstanding what you're saying, but it still doesn't quite seem to work.
You got it, DM has no efficient way of losing energy, that's why it's more diffuse. I still don't understand why the fixation with earth; if anything it would be attracted to the sun in the solar system, not the earth (or earth-moon). Besides that, there are millions of other stars way more massive than the sun. Given the collisionless nature of DM, it would most likely follow the denser regions. And models of structure formation predict that there are subhalos within the halo, exactly what you are saying. And we see that the distribution is not totally uniform. But, as we both agreed that DM is collisionless, the substructures formed are larger than that of ordinary matter.
The (possible) reason that there's more DM in the center it's because the halo was formed by gravitational collapse. It grew later on by mergers or pure accretion.

15
##### Flat Earth Investigations / Re: Fixed Planetary Mass and Dark Matter
« on: July 11, 2018, 11:11:19 PM »
The problem is that regular matter would be subject to the same forces; as dark matter was drawn to those fluctuations, it would be too. Sure, it may be less efficient if it occurs in that sweet spot where matter's moved beyond the subatomic, but how could a galaxy form with that halo dragging everything outwards?
I'm aware of the fact that an equal gravitational pull from all directions has net force zero, but that's only going to be the case for a hollow perfect sphere, and even then only for objects right in the middle. No kind of orbit could form around anything when the dust cloud would just be pulled outwards.
First, the bold part is wrong. A hollow uniform sphere has zero gravitational force anywhere inside, not just the middle.

Now to the main part: while ordinary matter is subject to the same forces as DM, the opposite is not true. Ordinary matter has pressure, friction and is subject to the EM force, all of which are important in the process of losing energy and creating compact objects such as planets and stars. Also, the structure formation is continuous; while density fluctuations grow and attract more DM, it also attracts more baryonic matter (in smaller quantities), up until they reach a critical density and collapse. As with any gravitational collapse, the center of the collapsed object is the densest, not the outer parts. The halo will keep growing by accretion or mergers, and at some point the universe will have cooled enough so that ordinary matter can make gravitationally bound structures, and so on until the galaxy is formed. For cold DM, the structure formation is called bottom-up: first smaller structures are formed, then grow through mergers or accretion.
We can therefore expect that the density profile of ordinary and dark matter roughly matches (with DM decreasing a lot more slowly); we do not expect DM to form objects of the size of planets or stars however, and will remain diffuse in a large ellipsoidal halo

16
##### Flat Earth Investigations / Re: Fixed Planetary Mass and Dark Matter
« on: July 11, 2018, 02:57:34 AM »
A key tenet of RET is dark matter; without such an entity the whole model falls apart. And further, it is true that dark matter is supported by evidence when the world is viewed from the RE perspective, the only way to make sense of the motion of planets and stars (supposedly due to gravity) is by recourse to these dark bodies.
The earliest reference I can find to dark matter as a vague concept is 1884, though this was very slight.
Dark matter only is only needed to explain the motion of stars within galaxies. There's absolutely no need for dark matter to explain anything in the solar system, and therefore dark matter is not a key tenet for round earth. If dark matter does not exist in any form and we actually need to revise general relativity, the new theory would have to have GR as its limit when applied to solar systems, much in the same way GR tends to newtonian gravity if we are dealing with small enough velocities and weak gravitational fields.

So where is its impact on calculations of the Earth's mass? RET does have excuses, but none of them can explain why it is dark matter fails to be attracted to centers of mass like planets. The moon doesn't simply stop orbiting the Earth just because the Sun or Galactic Center exist. If dark matter exists, it should be drawn to stars, moons, planets, according to RET.
There are some estimates of dark matter density in the solar system. Even if you take the upper limits, the amount of dark matter on earth would be around 10-18 times the total mass, completely negligible and undetectable. But why didn't DM clump together as ordinary matter, you might ask?
This is a bit of speculation (I'm no physicist, this is what I understand from reading about the subject). When the universe was hot and small, everything was nearly homogeneous, with small density fluctuations. As the universe expanded, these tended to grow by attracting matter of both kinds from regions around it. But DM is far more abundant than normal matter, so these small density flucutation were growing by pulling more and more DM. But here's the thing: DM is collisionless, and therefore exerts no pressure and it lacks an efficient way of losing energy. So as the density fluctuations grow larger, DM is pulled into it forming a dense cloud (it cannot form solids) that grows more and more, which then pulls also more ordinary matter, up until the point where the universe cooled enough so that structures could be formed. So DM clouds came BEFORE we had actual galaxies, it's ordinary matter that followed the gravitational wells of dark matter, not the other way around. And the reason that DM forms halos is because is frictionless (in addition to not being subject neither to the strong or electromagnetic force), so even if DM is being compacted or falling toward another object, it would just heat up and increase its velocity, not being bounded by the compact object being formed.
But, it does clump in some way; there are subhalos inside the halo, probably some DM filaments. As to why they formed like these, maybe noone knows, or maybe we all would need a course in structure formation to understand, I have no idea.

On a side note, normal neutrinos are probably not the main component of DM: since they move too fast, they wouldn't be able to form structures of the size of galaxies, only clusters.

17
##### Philosophy, Religion & Society / Re: Anselm's ontological argument
« on: June 04, 2014, 10:39:19 AM »
Wasn't there a parody of this ontological argument that "proves" god doesn't exist? I remember reading it somewhere, it goes more or less like this:
1 - The creation of the universe is the most wonderful achievement imaginable
2 - The greater the handicap of the creator, the more impressive is the achievement
3 - The greatest handicap possible is non-existence
4 - If we imagine that there is a creator for the universe, we can imagine a greater being that doesn't exist and still created everything
5 - An existing god is therefore not the greatest being we can conceive, since a more impressive god would be one that created everything while non existing
6 - God doesn't exist

18
##### Flat Earth Community / Re: Newton's Laws of Motion
« on: June 02, 2014, 01:23:03 AM »
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The term linear has nothing to do with the movement
This part is just wrong.
This whole discussion is basically a discussion on semantics but you're wrong. In usual terminology, linear acceleration is any change in velocity, which is a vectorial quantity. Therefore, any rotational movement will have linear acceleration.
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Did you maybe forget that the object in a perfectly circular orbit is still accelerating, at a right angle to its instantaneous velocity, toward the center of the orbit? If it weren't, it would fly off (standard pedantic disclaimer on FoRs) and not be in orbit any longer.
No, and that's why I said that any object in uniform circular motion will have a non zero linear acceleration.

19
##### Flat Earth Community / Re: Newton's Laws of Motion
« on: June 01, 2014, 10:57:19 PM »
No REer has suggested describing rotational motion as simple linear motion (I think that what you meant by "linearly".).

Your whole schpiel has been that the ISS has linear acceleration relative to the earth. Do you mean to say that its motion relative to the earth isn't rotational?

Think hard about that. Your previous response indicates their is a severe gap in your critical thinking.
No. The ISS rotates about the RE. Why do you ask? Do you think an object can't rotate about the RE and have linear acceleration?
ur dense
Someone correct me if I'm wrong, but as far as I know linear acceleration is just the force divided by the mass, and it's the second derivative of the position vector w.r.t. time. Since there's only one force acting on the ISS and its velocity vector changes with time, it follows that it does have linear acceleration. The term linear has nothing to do with the movement, it's just to differentiate it from angular acceleration, which can be defined as the torque divided by the moment of inertia, or the derivative of the angular velocity w.r.t. time. Any object in uniform circular motion has a non-zero linear acceleration and zero angular acceleration.

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##### Flat Earth Community / Re: Newton's Laws of Motion
« on: May 31, 2014, 02:57:39 PM »
I can see why Thork dropped out of this conversation, you people just refuse to read the posts and assume they say something they don't.  Angular acceleration is what has been talked about this entire time.  Go back through and read the posts and you'll see that.
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The ISS doesn't accelerate. Its in low earth orbit at a constant speed of around 17000mph To have a force of acceleration in one direction and an opposing force that cancels that out in the opposite direction does not mean one is accelerating. If I get in my car and accelerate to 150mph before the wind resistance is so great my car stops accelerating doesn't mean I am still accelerating. It means I am now at 150mph and that is that as the forces balanced.
You are confusing angular velocity with angular acceleration.
https://en.wikipedia.org/wiki/Angular_velocity
He says VERY clearly that the ISS doesn't accelerate and that the forces on it are balanced. If he was talking about angular acceleration, he should have added the word angular, which he did not. Therefore it'safe to assume he was talking in the more general sense of acceleration.

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