Offline fisherman

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Question about the Vomit Comet
« on: April 27, 2021, 09:57:51 PM »
Hoping one of you good people who are familiar with how the Vomit Comet works can clear something up for me.

My understanding is that during parabolic motion, thrust and drag cancel each other out and lift is reduced to zero because of the angle. That leaves just gravity working on the plane and since the plane and the occupants are falling together, there is a sensation of weightlessness.

I don't see how this could work with FE/UA.  Without any other forces to counteract it, the UA force should continue to accelerate the plane up, pushing the floor of the plane up and creating the sensation of weight.

Essentially, no different than our friend in the enclosed rocket ship that can't tell if he's being accelerated up or gravity is pulling him down.
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Offline WTF_Seriously

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Re: Question about the Vomit Comet
« Reply #1 on: April 28, 2021, 02:22:31 PM »

I don't see how this could work with FE/UA.  Without any other forces to counteract it, the UA force should continue to accelerate the plane up, pushing the floor of the plane up and creating the sensation of weight.


In essence, UA is just another form of drag.  If thrust can overcome drag, there's no reason to believe it doesn't also overcome UA.
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Offline fisherman

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Re: Question about the Vomit Comet
« Reply #2 on: April 28, 2021, 02:58:51 PM »
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In essence, UA is just another form of drag.  If thrust can overcome drag, there's no reason to believe it doesn't also overcome UA.

I was thinking more like UA is thrust...that you can never adjust or turn off like you can a rocket engine.  In order to be in free fall, thrust and drag must be equal.  Since you can't adjust the thrust UA causes, how do you equalize the drag so that the plane is in freefall?

Don't know enough about how it works, which is why I asked.
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Offline WTF_Seriously

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Re: Question about the Vomit Comet
« Reply #3 on: April 28, 2021, 03:49:36 PM »
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In essence, UA is just another form of drag.  If thrust can overcome drag, there's no reason to believe it doesn't also overcome UA.

I was thinking more like UA is thrust...that you can never adjust or turn off like you can a rocket engine.  In order to be in free fall, thrust and drag must be equal.  Since you can't adjust the thrust UA causes, how do you equalize the drag so that the plane is in freefall?

Don't know enough about how it works, which is why I asked.

Thrust/drag doesn't really matter.  Think RE.  To simulate freefall, the plane must overcome aerodynamic drag while equaling acceleration due to gravity.  In FE, the plane must overcome aerodynamic drag while equalling acceleration due to UA.  In either model, those would be the two things acting to simulate freefall, no?
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Online SteelyBob

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Re: Question about the Vomit Comet
« Reply #4 on: April 28, 2021, 04:19:52 PM »
My understanding is that during parabolic motion, thrust and drag cancel each other out and lift is reduced to zero because of the angle. That leaves just gravity working on the plane and since the plane and the occupants are falling together, there is a sensation of weightlessness.

Nearly. Yes, thrust will be adjusted to pretty much cancel out drag - this prevents the occupants from falling forwards or backwards with respect to the fuselage.  Speed will still reduce because of the component of weight acting along the aircraft's flightpath axis - a ballistic profile. The angle of attack is controlled to give zero lift, starting at around 45 degrees nose up and ending at around 45 nose down - the pilot pushes forward on the controls until 0gz is achieved.

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I don't see how this could work with FE/UA.  Without any other forces to counteract it, the UA force should continue to accelerate the plane up, pushing the floor of the plane up and creating the sensation of weight.

Whilst I disagree with the FE/UA proposition in the strongest possible terms, of all the many things that are obviously wrong with it, this isn't it. In a FE/UA world, the earth and the atmosphere would be accelerating upwards. To fly normally, aircraft would need to generate lift just as they currently do. A ballistic flight profile would work in just the same way.

I think the point you are missing is that the UA 'force' is deemed to only act on the earth - everything else is then pushed up by the earth. You are correct, in that if UA pushed on everything, then the parabolic flight profile wouldn't work. But then nor would anything - just walking around on the ground wouldn't work.

« Last Edit: April 28, 2021, 04:31:28 PM by SteelyBob »

Offline c0i9z

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Re: Question about the Vomit Comet
« Reply #5 on: April 28, 2021, 04:25:57 PM »
You have to remember that universal acceleration is not actually universal. Only some things get directly accelerated. Specifically, all the things that it's difficult to interact with directly. Planets, stars, whatever is supposed to be under the Earth that's actually experiencing the acceleration. All the things you might have actual experience with, like rocks, plants, animals, water, air, planes, etc. aren't apparently affected, for some mysterious reason. Otherwise, you'd get rocks that hover when they're dropped, something which I don't recall ever seeing.

Offline fisherman

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Re: Question about the Vomit Comet
« Reply #6 on: April 28, 2021, 05:48:25 PM »
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I think the point you are missing is that the UA 'force' is deemed to only act on the earth - everything else is then pushed up by the earth. You are correct, in that if UA pushed on everything, then the parabolic flight profile wouldn't work
.

Well, maybe it is the UA/FE model I don't understand.  But from other discussions, mostly about skydiving, I thought that the UA force accelerated the atmosphere along with the earth and that anything in the atmosphere accelerates along with it.  And that the reason that the earth eventually "catches up" is because drag slows down the acceleration of whatever is in the atmosphere.  It is accelerating at a slower rate, so eventually the earth is able to cover the distance between them.

The wiki defines terminal velocity as ‘When the acceleration of the falling object is equal to the acceleration of the Earth, the object has reached terminal velocity relative to the Earth.’

A “falling object” is being accelerated...by something other than gravity.  The Vomit Comet is a “falling object” what’s accelerating it? The whole concept of terminal velocity in UA makes it impossible to use the same formula in UA than gravity, but that's a different thread.

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All the things you might have actual experience with, like rocks, plants, animals, water, air, planes, etc. aren't apparently affected, for some mysterious reason. Otherwise, you'd get rocks that hover when they're dropped, something which I don't recall ever seeing.

The UA force doesn’t work directly on thing on the surface of the earth, but it does effect them.  Otherwise, the “pinning force” that is described in the wiki wouldn’t be necessary.  That’s their explanation for why we don’t see things hover.

Go back to the often used analogy used to describe the EP.  The closed box has no other force on it other than it is being accelerated up by some force and that causes whatever is in the box to become  pinned to the floor.

A plane in parabolic flight is the equivalent of the closed box.  It has no other force on it other than it is being accelerated up by some force.  If that force causes the person in the box (who isn’t being directly accelerated) to be pinned to the floor, the same thing should happen to people in the plane, who also aren’t directly effected by the accelerating force.


EDIT: Another thing to consider is that even if the plane is neither accelerating upn or accelerating down, its going to take a lot less than the 45 seconds or so that the plane is in freefall before an earth accelerating up at 1g to slams into it.
« Last Edit: April 28, 2021, 06:20:45 PM by fisherman »
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Online SteelyBob

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Re: Question about the Vomit Comet
« Reply #7 on: April 28, 2021, 06:39:13 PM »
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I think the point you are missing is that the UA 'force' is deemed to only act on the earth - everything else is then pushed up by the earth. You are correct, in that if UA pushed on everything, then the parabolic flight profile wouldn't work
.

Well, maybe it is the UA/FE model I don't understand.  But from other discussions, mostly about skydiving, I thought that the UA force accelerated the atmosphere along with the earth and that anything in the atmosphere accelerates along with it.  And that the reason that the earth eventually "catches up" is because drag slows down the acceleration of whatever is in the atmosphere.  It is accelerating at a slower rate, so eventually the earth is able to cover the distance between them.

The wiki defines terminal velocity as ‘When the acceleration of the falling object is equal to the acceleration of the Earth, the object has reached terminal velocity relative to the Earth.’

A “falling object” is being accelerated...by something other than gravity.  The Vomit Comet is a “falling object” what’s accelerating it? The whole concept of terminal velocity in UA makes it impossible to use the same formula in UA than gravity, but that's a different thread.

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All the things you might have actual experience with, like rocks, plants, animals, water, air, planes, etc. aren't apparently affected, for some mysterious reason. Otherwise, you'd get rocks that hover when they're dropped, something which I don't recall ever seeing.

The UA force doesn’t work directly on thing on the surface of the earth, but it does effect them.  Otherwise, the “pinning force” that is described in the wiki wouldn’t be necessary.  That’s their explanation for why we don’t see things hover.

Go back to the often used analogy used to describe the EP.  The closed box has no other force on it other than it is being accelerated up by some force and that causes whatever is in the box to become  pinned to the floor.

A plane in parabolic flight is the equivalent of the closed box.  It has no other force on it other than it is being accelerated up by some force.  If that force causes the person in the box (who isn’t being directly accelerated) to be pinned to the floor, the same thing should happen to people in the plane, who also aren’t directly effected by the accelerating force.

The issue is that normal newtonian physics only works in an inertial reference frame. For normal everyday calculations, we can consider earth to be inertial frame of reference (it's actually not quite, but close enough), with a gravity force equal to mg acting on everything. With that in place, all the maths makes sense.

FE/UA turns that on its head. In it, everything is being accelerated by, as I understood it, the earth. It is as if we are floating in space in a spaceship which then fires its rocket engine and starts accelerating at 1g - we all squash down to the base of the spaceship for as long as it accelerates. If the cabin of the spaceship was pressurised, then there would be a pressure gradient, albeit a very small one, detectable in the 'atmosphere'.

In that environment, we would no longer be in an inertial frame of reference, because everything is accelerating. So if I throw a ball to you, it doesn't just fly horizontally with respect to the spaceship, but rather 'falls'. Terminal velocity, in that context, would be achieved when the drag force acting on the object was equal to mg - exactly the same as on the inertial 'normal' planet earth.

So FEers are correct (for a change!) on this one - were we to exist on a UA/FE world, it would be indistinguishable from our current environment.

Indistinguishable, that is, apart from the stars and planets rotating beautifully around our celestial poles, and the massive discrepancy between observed distances between known points, and all the many other things that, aside from the actual footage of our beautiful round earth viewed from afar, clearly point to it being globe shaped.

Offline fisherman

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Re: Question about the Vomit Comet
« Reply #8 on: April 28, 2021, 08:50:41 PM »
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The issue is that normal newtonian physics only works in an inertial reference frame. For normal everyday calculations, we can consider earth to be inertial frame of reference (it's actually not quite, but close enough), with a gravity force equal to mg acting on everything. With that in place, all the maths makes sense.


Newton v Relativity has nothing to do with the point I am making.

If the plane is only subject to gravity, it will go into freefall and the occupants will “float”.  If the plane is only subject to UA, then the floor of the plane will be pinned against the occupants and they won’t float.

That’s true by Newtonian physics and also true according to relativity.

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So FEers are correct (for a change!) on this one - were we to exist on a UA/FE world, it would be indistinguishable from our current environment.

Indistinguishable, that is, apart from the stars and planets rotating beautifully around our celestial poles, and the massive discrepancy between observed distances between known points, and all the many other things that, aside from the actual footage of our beautiful round earth viewed from afar, clearly point to it being globe shaped.

A lot of Rers seem to buy into this notion as much as the Fers and its simply not true. I think it come from the belief that the EP, and relativity in general makes all motion relative. It doesn’t, It only makes unaccelerated motion relative.  Which overall, accounts for a small portion of the motion we see in real life.

So if the occupants in the Vomit Comet were being accelerated by the UA force, they’d know it, just like the guy in the closed box floating around in space.  If the floor came up and hit him or the he hit the floor, either way he knows he’s being accelerated.  He may not know why, but he knows he is.

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Terminal velocity, in that context, would be achieved when the drag force acting on the object was equal to mg - exactly the same as on the inertial 'normal' planet earth.

The difference is If terminal velocity is defined as “when the falling object is accelerating at the same rate as the earth”...then the falling object is still accelerating, which means its velocity continues to increase.  As opposed to the RE/gravity concept of terminal velocity… when an object is no longer accelerating and its velocity stops increasing. You’d have to use two different formulas to determine those two very different things.

Anyway, back to my original question.  It seems like it boils down to whether or not the UA force would cause the atmosphere to accelerate and the plane along with it.
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Offline WTF_Seriously

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Re: Question about the Vomit Comet
« Reply #9 on: April 28, 2021, 09:03:39 PM »

If the plane is only subject to gravity, it will go into freefall and the occupants will “float”.  If the plane is only subject to UA, then the floor of the plane will be pinned against the occupants and they won’t float.

So if the occupants in the Vomit Comet were being accelerated by the UA force, they’d know it,....

Here's where you're misunderstanding UA.  Someone mentioned the issue before.  Not in any way discussing the validity or possibility of the effect.

The plane and the person are NOT being accelerated by UA.  That is why they 'fall'.  Only the earth is being accelerated by UA.  The earth, in turn, pushes the atmosphere up with it.  In FE, a plane flies because the lift generated causes it to accelerate upward at the same rate as the air column, being pushed up by the earth, surrounding it.  The person inside the aircraft is pinned to the aircraft's floor because that person is not naturally accelerated upward by UA.

Once thrust is reduced, the plane loses the lift ability to maintain the upward acceleration.  When enough thrust is reduced, the acceleration of the plane upward will become zero, the same as the passenger.  This results in weightlessness.
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Offline fisherman

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Re: Question about the Vomit Comet
« Reply #10 on: April 28, 2021, 10:38:52 PM »
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The plane and the person are NOT being accelerated by UA.

Well, like i said, that seems to be thrust of the issue :).  The wiki implies that the plane and the person would be accelerated by UA.  It would be nice if an FEr would clarify.

The wiki defines terminal velocity as When the acceleration of the falling object is equal to the acceleration of the Earth, the object has reached terminal velocity relative to the Earth.  And note that it's in the "universal acceleration" section of the wiki.  To me that implies that under UA, a "falling object" is being accelerated.

I want to clarify this statement.

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With that in place, all the maths makes sense

The maths only make sense if you are considering unaccelerated motion. GR divides all motion into geodetic, unaccelerated motion that is traveling along the straightest possible path under no force and non-geodetic, accelerated motion not along the straightest possible path and under a force.

No change of perspective, manipulation of coordinates or maths can change one into the other.  Geodetic motion will always have the straightest possible worldline, non-geodetic will not.  If you plot the worldline of an earth that is not under any force, you will get the straightest possible path through spacetime. If you plot the worldline of an earth that is under acceleration by UA, you will get something other than the straightest possible line.

That is what the maths show according to GR. An earth under acceleration will follow a hyperbola. An earth not under acceleration will not.
« Last Edit: April 28, 2021, 10:44:10 PM by fisherman »
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Offline fisherman

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Re: Question about the Vomit Comet
« Reply #11 on: April 28, 2021, 11:04:43 PM »
A question for anyone who can answer, but from an FE would be nice..

If "When the acceleration of the falling object is equal to the acceleration of the Earth, the object has reached terminal velocity relative to the Earth".

doesn't mean that a "falling object" is accelerated by UA, what does it mean?
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Online SteelyBob

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Re: Question about the Vomit Comet
« Reply #12 on: April 29, 2021, 06:10:52 AM »
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The issue is that normal newtonian physics only works in an inertial reference frame. For normal everyday calculations, we can consider earth to be inertial frame of reference (it's actually not quite, but close enough), with a gravity force equal to mg acting on everything. With that in place, all the maths makes sense.


Newton v Relativity has nothing to do with the point I am making.

If the plane is only subject to gravity, it will go into freefall and the occupants will “float”.  If the plane is only subject to UA, then the floor of the plane will be pinned against the occupants and they won’t float.

That’s true by Newtonian physics and also true according to relativity.

I entirely agree - I wasn't bringing relativity into this. I'm simply talking about an inertial reference frame - a frame of reference, or datum, that is not accelerating. So the surface of our earth is a good inertial reference point (ignoring very small error due to rotation and the centripetal acceleration towards the sun - barely measurable). You could also use a vehicle travelling at constant speed. To borrow from another thread, you and I could play table tennis on a moving bullet train, and the ball would fly just as it would if we were at rest in a station. To calculate the ball's motion we could choose the train as a reference point - a valid choice, as it is inertial (ie non accelerating),and a wise one, as it keeps things simple - we measure all velocities etc with respect to the train. We could if wished, choose the earth, but then things get complex, because all the velocities would have the motion of the train superimposed on them, meaning a negative velocity with respect to the train might still be positive with respect to the earth.

But it all breaks down if the train accelerates. If you hit the ball to me and the train brakes suddenly, then the motion of the ball with respect to the train will not be what we would expect at all - we would have to choose the earth as a datum, or perhaps compensate for the acceleration in our calculations - engineers sometimes use d'Alembert forces to do this. You sometimes see it being done with circular motion - they add a 'centrifugal' d'Alembert force, even though no such thing exists, to change an accelerating reference frame into an inertial one.

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If "When the acceleration of the falling object is equal to the acceleration of the Earth, the object has reached terminal velocity relative to the Earth".
doesn't mean that a "falling object" is accelerated by UA, what does it mean?

Again, the FEers are sort of, oddly correct here. The whole thing is nonsense, clearly, but as a thought exercise it does work.

Remember, the earth in UA/FE is not an inertial reference frame - you can't do newtonian maths with respect to the surface and expect things to work. So we have to imagine ourselves outside the earth, stationary, watching it accelerate past our fixed datum point. The earth is accelerating 'up' at 1g. The earth's atmosphere will eventually achieve a steady state whereby it ends up with a pressure/density gradient just like our atmosphere does on our beautiful, globe-shaped earth. Once stabilised in that state, it too will accelerate at 1g - every small 'parcel' of air will experience a net 'mg' force pushing it up. So we have a planet and an atmosphere accelerating upwards at 1g. If you then drop a ball from a hot air balloon or similar, the ball will initially be stationary with respect to the balloon, so it will have whatever velocity with respect to us observing that the earth/atmosphere/balloon did at the point of release. But it will retain that velocity, while the atmosphere and balloon etc keep accelerating, and so will appear to 'fall' from our perspective. As it falls it will start to experience a force, increasing with the square of the velocity difference, as the air rushes past it. At some point the drag force will reach mg, at which point the ball's upward acceleration will equal that of earth/atmosphere/balloon. However, it will retain a constant velocity difference. With respect to the earth's surface it is falling at terminal velocity. With respect to us, it is accelerating upwards at the same rate as the earth/atmosphere/balloon, but is at a slightly lower velocity. So the earth might be going at 1000m/s, and our ball might be going at 970m/s, with each adding 9.8m/s to their speed every second - the ball has a terminal velocity of 30m/s.

Note: none of the above obviates the numerous issues with the UA model, or indeed the many obvious flaws in the FE model generally.

Offline fisherman

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Re: Question about the Vomit Comet
« Reply #13 on: April 29, 2021, 01:28:26 PM »
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The issue is that normal newtonian physics only works in an inertial reference frame. For normal everyday calculations, we can consider earth to be inertial frame of reference (it's actually not quite, but close enough), with a gravity force equal to mg acting on everything. With that in place, all the maths makes sense.


Newton v Relativity has nothing to do with the point I am making.

If the plane is only subject to gravity, it will go into freefall and the occupants will “float”.  If the plane is only subject to UA, then the floor of the plane will be pinned against the occupants and they won’t float.

That’s true by Newtonian physics and also true according to relativity.

I entirely agree - I wasn't bringing relativity into this. I'm simply talking about an inertial reference frame - a frame of reference, or datum, that is not accelerating. So the surface of our earth is a good inertial reference point (ignoring very small error due to rotation and the centripetal acceleration towards the sun - barely measurable). You could also use a vehicle travelling at constant speed. To borrow from another thread, you and I could play table tennis on a moving bullet train, and the ball would fly just as it would if we were at rest in a station. To calculate the ball's motion we could choose the train as a reference point - a valid choice, as it is inertial (ie non accelerating),and a wise one, as it keeps things simple - we measure all velocities etc with respect to the train. We could if wished, choose the earth, but then things get complex, because all the velocities would have the motion of the train superimposed on them, meaning a negative velocity with respect to the train might still be positive with respect to the earth.

But it all breaks down if the train accelerates. If you hit the ball to me and the train brakes suddenly, then the motion of the ball with respect to the train will not be what we would expect at all - we would have to choose the earth as a datum, or perhaps compensate for the acceleration in our calculations - engineers sometimes use d'Alembert forces to do this. You sometimes see it being done with circular motion - they add a 'centrifugal' d'Alembert force, even though no such thing exists, to change an accelerating reference frame into an inertial one.

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If "When the acceleration of the falling object is equal to the acceleration of the Earth, the object has reached terminal velocity relative to the Earth".
doesn't mean that a "falling object" is accelerated by UA, what does it mean?

Again, the FEers are sort of, oddly correct here. The whole thing is nonsense, clearly, but as a thought exercise it does work.

Remember, the earth in UA/FE is not an inertial reference frame - you can't do newtonian maths with respect to the surface and expect things to work. So we have to imagine ourselves outside the earth, stationary, watching it accelerate past our fixed datum point. The earth is accelerating 'up' at 1g. The earth's atmosphere will eventually achieve a steady state whereby it ends up with a pressure/density gradient just like our atmosphere does on our beautiful, globe-shaped earth. Once stabilised in that state, it too will accelerate at 1g - every small 'parcel' of air will experience a net 'mg' force pushing it up. So we have a planet and an atmosphere accelerating upwards at 1g. If you then drop a ball from a hot air balloon or similar, the ball will initially be stationary with respect to the balloon, so it will have whatever velocity with respect to us observing that the earth/atmosphere/balloon did at the point of release. But it will retain that velocity, while the atmosphere and balloon etc keep accelerating, and so will appear to 'fall' from our perspective. As it falls it will start to experience a force, increasing with the square of the velocity difference, as the air rushes past it. At some point the drag force will reach mg, at which point the ball's upward acceleration will equal that of earth/atmosphere/balloon. However, it will retain a constant velocity difference. With respect to the earth's surface it is falling at terminal velocity. With respect to us, it is accelerating upwards at the same rate as the earth/atmosphere/balloon, but is at a slightly lower velocity. So the earth might be going at 1000m/s, and our ball might be going at 970m/s, with each adding 9.8m/s to their speed every second - the ball has a terminal velocity of 30m/s.

Note: none of the above obviates the numerous issues with the UA model, or indeed the many obvious flaws in the FE model generally.

Would quibble with a couple of points,  but none are relevant to this discussion.  The important point is that you acknowledge that an object in the atmosphere of an earth accelerating upwards, will also accelerate up. And it will accelerate up at 1g.

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Remember, the earth in UA/FE is not an inertial reference frame - you can't do newtonian maths with respect to the surface and expect things to work.


I’m not using Newtonian maths.  In relativity, the worldline of an accelerating earth (or anything accelerating at relativistic speeds) will be a hyperbola. The worldline of an an object accelerating at less than relativistic speed will not be a hyperbola, but it will be diagonal.  The worldline of an object that is not accelerating will follow tbe straightest possible path through spacetime.  In flat space spacetime, the worldline will be vertical, as an object at rest is moving through time but not through space. In curved space time, it will follow the curve of time, but won’t travel in space.

Frame of reference is irrelevant.  First of all, the occupants in the plane are in the same frame of reference as the plane, so if the plane is accelerating in its own frame, the occupants will experience that acceleration.  But more importantly acceleration is not relative .  If something is accelerating, it has a force on it.  Changing frames of reference doesn’t make that force go away.  It’s either there or it isn’t and objects and if its there, people being accelerated will experience the effects of the acceleration.  The perception of the force and the resulting velocities may be different in a different frame, but the fact of the force and the fact of acceleration doesn’t change.  Something is either accelerating due to a force or its not.  That is an absolute. No change in frame of reference changes that.  Clear enough?

So if, no matter what frame of reference you are in, the atmosphere is accelerating the plane up, at 1g, and is the only force on the plane how is it that the floor of the plane is not pushed against the occupants?
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Online SteelyBob

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Re: Question about the Vomit Comet
« Reply #14 on: April 29, 2021, 06:03:09 PM »
I’m not using Newtonian maths. 

I think that's the issue. Keep it simple - there's no need at all to invoke relativity at all to demonstrate that this works.

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Frame of reference is irrelevant.  First of all, the occupants in the plane are in the same frame of reference as the plane, so if the plane is accelerating in its own frame, the occupants will experience that acceleration. 
It's enormously relevant. If it's accelerating, then it isn't an inertial reference frame. You either need to pick an inertial reference point to measure displacement and velocities from, or you need to correct for the acceleration by means of d'Alembert-style inertial 'forces' that correct the errors.

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But more importantly acceleration is not relative .  If something is accelerating, it has a force on it. 
Agreed...but if the object is stationary and the earth is accelerating towards it then there's no force on it...

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Changing frames of reference doesn’t make that force go away. 

But this discussion is about the thought experiment of a permanently accelerating flat earth versus what we know and (I think?) agree to be the truth, which is a globe earth exerting a force on everything around it equal to mg. The question is whether objects would behave the same in the two systems - would they trace, for example, the same flightpath in ballistic flight? Would objects have the same apparent terminal velocity? These things require us to measure the displacement, s, relative to a fixed point on the earth's surface. So a ball dropped from height above our accelerating FE would experience no force at all - viewed from afar it would actually be stationary. And yet it would appear to accelerate towards the earth, despite having no force acting on it. The displacement between the earth and the ball would change at the same rate - it matters not whether the ball is accelerating, or the earth.

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So if, no matter what frame of reference you are in, the atmosphere is accelerating the plane up, at 1g, and is the only force on the plane how is it that the floor of the plane is not pushed against the occupants?

Because, like the dropped ball above, in the FE/UA case, viewed from a fixed point off the earth, the aircraft would be stationary (or rather, at a constant velocity) and the earth would be accelerating towards it. The atmosphere wouldn't be pushing on it, as the pilot is not demanding lift from the wings.

Make sense?

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Re: Question about the Vomit Comet
« Reply #15 on: April 29, 2021, 07:16:21 PM »
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Make sense?

No.  Because of the point I keep making and you keep ignoring is that frame of reference is irrelevant

From a fixed point on the earth the plane would not appear to be stationary or at a constant velocity because acceleration is not relative .  From a fixed point on the earth, the plane would appear to be accelerating at 1g because acceleration is not relative.  I can’t make it any clearer than that.  For your explanation to make sense, then acceleration must be relative, and its not.

Even, if it was.  That wouldn’t change what the plane and its occupants are experiencing.  So what if someone else on the surface doesn’t perceive that the plane is accelerating? What matters is whether or not the occupants experience acceleration.  Someone else’s perception of what they experience doesn’t change what they experience.

If someone in another frame of reference can’t perceive the plane’s acceleration, then according to you the acceleration doesn’t exist. By that logic, if the observer closes his eyes and can no longer observe the plane, the plane doesn’t exist. Not to get all philosophical, but it is fascinating to me the way people, FE and RE alike seem to think that someone's perception of your reality, changes your reality.
There are two kinds of people in the world.  Those that can infer logical conclusions from given information

Offline WTF_Seriously

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Re: Question about the Vomit Comet
« Reply #16 on: April 29, 2021, 07:40:05 PM »
So if, no matter what frame of reference you are in, the atmosphere is accelerating the plane up, at 1g, and is the only force on the plane how is it that the floor of the plane is not pushed against the occupants?

That's exactly what happens when the plane is in level flight and the occupants feel weight.  Just like a plane flying on RE.

During FE weightlessness, the thrust of the plane is such that it is forcing itself through the accelerating atmosphere in order to remain motionless just like the passengers.

Step outside the dome for a moment and position yourself stationary as you watch the approaching earth.  Earth plane and passenger are all approaching you at acceleration = G. Plane is in level flight and it's passengers are pinned to the floor experiencing weight.  This occurs because only the earth is affected by UA, not the plane and passengers.  At the moment the plane is level with you, the pilot slams the plane downward at acceleration = G.  You will see the plane and passengers stop motionless as the earth continues to rise to meet them.  At this time, the passengers will not feel pinned to the floor as neither they nor the plane is accelerating upwards any longer.


Edited to add:  Had to change my thought slightly.  When the pilot thrusts the plane downward, the plane and passenger will continue at constant velocity not stop entirely.  The key is that they will cease accelerating thus the weightless feeling.
« Last Edit: April 29, 2021, 08:07:04 PM by WTF_Seriously »
Lol "Everyone is Wrong and LiEeInG"
That is a desperate argument from a losing position. An argument from a position of strength would have positive evidence for that position.

Offline fisherman

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Re: Question about the Vomit Comet
« Reply #17 on: April 29, 2021, 08:13:26 PM »
Quote
During FE weightlessness, the thrust of the plane is such that it is forcing itself through the accelerating atmosphere in order to remain motionless just like the passengers.

There is no thrust in parabolic flight.  Thrust and drag cancel each other out.
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This occurs because only the earth is affected by UA, not the plane and passengers.

I already showed how that is not the case according to RE theory.  A falling object accelerates.  It says that plainly on the wiki.
There are two kinds of people in the world.  Those that can infer logical conclusions from given information

Online SteelyBob

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Re: Question about the Vomit Comet
« Reply #18 on: April 29, 2021, 08:17:43 PM »
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Make sense?
No.  Because of the point I keep making and you keep ignoring is that frame of reference is irrelevant
No, that's not fair - I'm certainly not ignoring it. I'm disagreeing with you, and that's fine - this is a debating forum, after all. Again, frame of reference is enormously important - if it's accelerating, it ain't inertial.

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From a fixed point on the earth the plane would not appear to be stationary or at a constant velocity because acceleration is not relative .  From a fixed point on the earth, the plane would appear to be accelerating at 1g because acceleration is not relative.  I can’t make it any clearer than that.  For your explanation to make sense, then acceleration must be relative, and its not.

Even, if it was.  That wouldn’t change what the plane and its occupants are experiencing.  So what if someone else on the surface doesn’t perceive that the plane is accelerating? What matters is whether or not the occupants experience acceleration.  Someone else’s perception of what they experience doesn’t change what they experience.

If someone in another frame of reference can’t perceive the plane’s acceleration, then according to you the acceleration doesn’t exist. By that logic, if the observer closes his eyes and can no longer observe the plane, the plane doesn’t exist. Not to get all philosophical, but it is fascinating to me the way people, FE and RE alike seem to think that someone's perception of your reality, changes your reality.

Ok let's try putting some numbers on it to see if it helps.

Imagine we're on a spaceship, that isn't accelerating, just floating in space, watching the earth, atmosphere and plane accelerate past us, from left to right. Let's say, for the sake of argument, that the acceleration hasn't being going on for very long, and the whole system is travelling at 1000m/s, increasing by 9.8m/s every second. The earth is being pushed by some mysterious force, the atmosphere is being pushed by the earth, the wings are being pushed by the atmosphere, the fuselage by the wings, the seats by the fuselage, the passengers by the seats. And so on.

From our position, we see an accelerating earth/atmosphere system whizz by at an ever increasing velocity. So far so good - agree?

Then, let's imagine that at the precise moment earth hits 1000m/s (relative to our datum on the spaceship) the pilot pushes forward on his controls until the accelerometer on his instrument panel reads '0g'. He throttles back to keep a roughly constant speed. The plane, from our position, retains its 1000m/s velocity. The earth continues to accelerate. After 1 second, the earth is now doing 1009.8m/s, increasing constantly, but our plane remains at 1000m/s left to right. The passengers feel weightless, because there is no force acting on them. From the viewpoint of a person on earth, the aircraft would appear to be ballistic, in a descending parabola, until the pilot recovers from the dive or the aircraft crashes.

And this is the key point - from the point of view of somebody in the earth/atmosphere/plane system, there is no discernible difference between a stationary earth exerting 1g and an ever accelerating earth - all the forces, all the relative velocities - it's all the same. That doesn't of course mean the earth is flat.

Offline WTF_Seriously

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Re: Question about the Vomit Comet
« Reply #19 on: April 29, 2021, 08:27:51 PM »
There is no thrust in parabolic flight.  Thrust and drag cancel each other out.

No.  There is thrust.  Thrust = Drag that is how they cancel each other out.

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I already showed how that is not the case according to RE theory.  A falling object accelerates.  It says that plainly on the wiki.

We're not talking about RE theory.  We're talking about UA/FE theory.  In UA/FE theory, UA doesn't act upon the plane and passenger.  If it did then each would naturally float.  'Falling' in FE is earth accelerating to meet object as opposed to object accelerating to meet earth.  The two are equivalent.
Lol "Everyone is Wrong and LiEeInG"
That is a desperate argument from a losing position. An argument from a position of strength would have positive evidence for that position.