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Galilean relativity, or is there such thing as absolute motion?


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3 hours ago, truthseeker said:

The cart advancing up the treadmill is Galilean equivalent to (so exactly the same as) the same cart going directly downwind faster than the wind.  Its not doing it outside and it's very small and light and the wind is perfectly steady, but it's doing it.

No, it is not a case of Galilean relativity. What does “Galilean equivalent” even mean to you?

I will repeat what I wrote earlier: Galilean relativity only speaks about observing one and the same experiment from two or more different frames of reference. There can be no physical difference because it is always just the one and the same situation. Only the reference frames of the observers are different.

What you are doing is observing and comparing two different experiments, one inside on a treadmill and the other outside on the ground in a wind. There is no law in physics that says the results of these two different experiments will be the same. There is no possible way you can guarantee that you have duplicated all the parameters so the experiments are the same.

You are making up your own version of Galilean equivalence, which you will not find in any textbook on Physics.

The cart going up the treadmill belt has absolutely nothing to do with wind. An observer moving with the belt, in the same direction as the belt, will feel a relative wind. The cart never moves with the belt in the direction of the belt and never feels any wind! It is held down on  the belt until the propeller develops a store of rotational energy, then it is released. The exact mechanism for how it continues to advance has never been investigated in a thorough scientific manner. That should be done before any wild claims are made about going faster than the wind.

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8 hours ago, OceanBreeze said:

No, it is not a case of Galilean relativity. What does “Galilean equivalent” even mean to you?

I will repeat what I wrote earlier: Galilean relativity only speaks about observing one and the same experiment from two or more different frames of reference. There can be no physical difference because it is always just the one and the same situation. Only the reference frames of the observers are different.

What you are doing is observing and comparing two different experiments, one inside on a treadmill and the other outside on the ground in a wind. There is no law in physics that says the results of these two different experiments will be the same. There is no possible way you can guarantee that you have duplicated all the parameters so the experiments are the same.

You also suggested in your previous post that there is a difference... but didn't say what the difference was. If there is a difference, what is it? 

8 hours ago, OceanBreeze said:

You are making up your own version of Galilean equivalence, which you will not find in any textbook on Physics.

I don't have any textbooks handy but Wikipedia, for example, says "Galilean invariance or Galilean relativity states that the laws of motion are the same in all inertial frames." This means that the laws are the same in the frame that is fixed to the air, as in the frame that is fixed the ground. This in turn means that if you have a vehicle running on the ground with a natural tailwind to match the air's speed, so that there is no relative wind (Let's call this situation E), the laws are the exact same as with one running on a treadmill with no natural wind, meaning a relative tailwind (F) and it is indeed guaranteed that the results will come out the same. The forces on the vehicle (from the air and from the ground) are the same, so what would be the source of any difference in result?

(there could of course be differences based on size like Reynolds number, or ones based on ground texture and what-not, but they have nothing to do with the "which thing is moving" question, and the result would be the same if the size, surface texture, etc., is duplicated from one run to the other). Am I going wrong anywhere here?

If the "which thing is moving" question matters, then doesn't this also invalidate wind tunnels?

8 hours ago, OceanBreeze said:

The cart going up the treadmill belt has absolutely nothing to do with wind. An observer moving with the belt, in the same direction as the belt, will feel a relative wind. The cart never moves with the belt in the direction of the belt and never feels any wind! It is held down on  the belt until the propeller develops a store of rotational energy, then it is released. The exact mechanism for how it continues to advance has never been investigated in a thorough scientific manner. That should be done before any wild claims are made about going faster than the wind.

Starting by being placed manually at zero speed relative to the air, is not necessary. Here is a video in which it self-starts (starts from zero speed relative to the ground.) https://www.youtube.com/watch?v=LABSbSTIEvM at about the 3:20 mark. And what about the other link from my previous post which casts aside all Galilean doubts by having the ground stay still and the air move? (and self-starts also)? How "wild" are claims about going faster than the wind, when the videos plainly show exactly this happening?

Edited by EfisCompMon
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I have not brought up any “the thing which is moving” question, because we are talking about relative motion. Nobody is making any claim for absolute motion.

I also understand that the law of physics are the same in all inertial frames of reference.

None of that guarantees the results of two different experiments will be the same! What they do guarantee is that one experiment with different observers in different reference frames making tests and measurements must come up with the same result, although they may not agree on the source of energy, or velocities, they will agree on forces and accelerations etc. I made that point in my earlier post about the turbine in the wind tunnel. All observers agree that it runs and produces the same amount of energy regardless of the observer’s frame of reference.

However, for two different experiments to yield the exact same results, the parameters must be exactly matched in both. How can you guarantee that is the case? How can you guarantee the forces on a wheel being driven by a belt are exactly the same as one being driven over the ground by wind force?

You are basically agreeing with me when you say : “(there could of course be differences based on size like Reynolds number, or ones based on ground texture and what-not, but they have nothing to do with the "which thing is moving" question, and the result would be the same if the size, surface texture, etc., is duplicated from one run to the other)”

That is exactly my point! The texture of an elastic belt that is driving a wheel cannot be duplicated by a wheel rolling on the ground. Nor can the forces exerted on the wheel by the belt be exactly duplicated by the wheel rolling on the ground. You can’t simply hand wave away those differences because even one small difference can cause a completely different result in the two experiments.

I should not even need to point out that the rotating table gizmo is not inertial, nor is it well balanced. There are all sorts of different forces going on there and it can be dismissed easily as a demo for ddw.

I don’t have time to go into detail now, maybe tomorrow I will have time to comment more.

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14 hours ago, OceanBreeze said:

I will repeat what I wrote earlier: Galilean relativity only speaks about observing one and the same experiment from two or more different frames of reference. There can be no physical difference because it is always just the one and the same situation. Only the reference frames of the observers are different.

I completely agree with this.

14 hours ago, OceanBreeze said:

What you are doing is observing and comparing two different experiments, one inside on a treadmill and the other outside on the ground in a wind.

No, I'm not.  I said explicitly that the treadmill cart is not outside.

14 hours ago, OceanBreeze said:

The cart going up the treadmill belt has absolutely nothing to do with wind.

Wind, by definition, is relative motion of air or gas with respect to a surface.  That surface doesn't have to be "the ground".  It can be the ocean's surface, or a layer or Jupiter's atmosphere, or the belt of a treadmill.  The fact that you don't understand this shows that you have not understood Galilean relativity.

 

14 hours ago, OceanBreeze said:

An observer moving with the belt, in the same direction as the belt, will feel a relative wind.

Precisely.  That's why there is in fact wind with respect to the treadmill belt, just as there is wind outside when the air moves with respect to the ground or ocean.

14 hours ago, OceanBreeze said:

The cart never moves with the belt in the direction of the belt and never feels any wind!

That depends on what the cart's state of motion is.  In its steady-state it is moving directly downwind faster than the wind and so it feels an apparent headwind.

 

14 hours ago, OceanBreeze said:

It is held down on  the belt until the propeller develops a store of rotational energy, then it is released. The exact mechanism for how it continues to advance has never been investigated in a thorough scientific manner. That should be done before any wild claims are made about going faster than the wind.

To establish that the cart can move ddw faster than the wind (steady state) simply requires the observation that it advances up the belt (steady-state).  That is not just EVIDENCE for ddw faster than the wind, it IS ddw faster than the wind.   This does not prove that the Blackbird can go ddw, or that the treadmill cart would necessarily work under any conditions other than the ones actually tested, but it does prove that ddw is possible and therefore cannot violate conservation of energy or any other law of physics.

Edited by truthseeker
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2 hours ago, OceanBreeze said:

I have not brought up any “the thing which is moving” question, because we are talking about relative motion. Nobody is making any claim for absolute motion.

Well, in your first post in the thread you distinguished between a wheel rolling on the ground from a wheel rolling on a treadmill:

Quote

A rolling wheel puts down a contact patch and normally must move by bringing that contact patch back and laying down another, in a continuous manner. It seems to me that on the treadmill belt, the belt will bring the contact patch back for the wheel, reducing the work done by the wheel in rolling. Indeed, this is how the belt forces the wheel to roll at all!

You seem to base this difference only on which thing is moving, as you don’t point to any of the other types of differences you mentioned elsewhere (materials, elasticity, etc.) to change the amount of force. If it matters for the mechanics and forces that the road surface is moving relative to some other surface a few inches lower, does it matter that it’s also moving relative to the center of the earth at 600 mph, or relative to the sun at 67,000 mph, etc? In other words, if the relative motion is the same between the wheel and the surface, then what else is in play?

But if you’ve had second thoughts about this distinction and retracted in favor of the position that only relative motion has an effect on forces and accelerations, then we’re in agreement so far.

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None of that guarantees the results of two different experiments will be the same!

Well, if we add the stipulation that in the two experiments compared, the are no differences in anything that can effect a force (materials, size, Reynolds number, etc.), and the only difference is which-thing-is-moving, then it seems that we are guaranteed an equal result. Agree/disagree?

So in my pairs A vs B, C vs D, and E vs F, notice I never said anything about different sizes or materials (although it’s easy for the mind to fill in those blanks with rubber belt vs pavement, a bigger vehicle in the outdoor environment, etc… so let’s be careful to only go with what’s specified, i.e., all those things are the same). With these stipulations in place, (same texture, same size) is there any cause to think the results would be different?

To summarize them again:

A/B: The air is NOT moving relative to the surface. The vehicle is moving relative to the surface, and relative to the air

C/D: The air IS moving relative to the surface. The vehicle is still relative to the surface, and moving relative to the air

E/F: The air IS moving relative to the surface. The vehicle is moving relative to the surface, and still relative to the air.

Quote

 

I should not even need to point out that the rotating table gizmo is not inertial, nor is it well balanced. There are all sorts of different forces going on there and it can be dismissed easily as a demo for ddw.

I don’t have time to go into detail now, maybe tomorrow I will have time to comment more.

 

I’m very curious to get your thoughts when you’re able. (Especially on the wind tunnel where the ground stays still and the air moves.) Obviously there’s an acceleration (not subject to Galilean relativity) toward the center, but in the forward-aft dimension, there isn’t. It’s very difficult to see how any of the imperfect balance would propel the cart downwind faster than the wind, in a way that this achievement would be made impossible if the balance was perfect.

Edited by EfisCompMon
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Moderator Note: I went to considerable trouble to move all the sh1t posts made by Autodidactocrat and JeffreysTubes8 (same person) to a new thread in silly claims where he can continue to talk to himself. If any more such posts are made in this thread, they will simply be deleted, and a warning and suspension given.

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16 hours ago, truthseeker said:

I completely agree with this.

No, I'm not.  I said explicitly that the treadmill cart is not outside.

Wind, by definition, is relative motion of air or gas with respect to a surface.  That surface doesn't have to be "the ground".  It can be the ocean's surface, or a layer or Jupiter's atmosphere, or the belt of a treadmill.  The fact that you don't understand this shows that you have not understood Galilean relativity.

 

Precisely.  That's why there is in fact wind with respect to the treadmill belt, just as there is wind outside when the air moves with respect to the ground or ocean.

That depends on what the cart's state of motion is.  In its steady-state it is moving directly downwind faster than the wind and so it feels an apparent headwind.

 

To establish that the cart can move ddw faster than the wind (steady state) simply requires the observation that it advances up the belt (steady-state).  That is not just EVIDENCE for ddw faster than the wind, it IS ddw faster than the wind.   This does not prove that the Blackbird can go ddw, or that the treadmill cart would necessarily work under any conditions other than the ones actually tested, but it does prove that ddw is possible and therefore cannot violate conservation of energy or any other law of physics.

I know very well what wind and what Galilean relativity is. I am saying the cart on the treadmill is never powered by wind energy; all of the cart’s energy is coming from the moving belt, all the time. This is true regardless of what inertial reference frame you use, even the one where you claim the belt is not moving! Why? Because the wheels are turning in every inertial frame you use, and it must be the belt that is turning those wheels, because there is no other force or source of energy acting on the cart.

The cart never moves with the belt, in the direction of the belt, so never experiences a tailwind. The headwind is not a source of energy, it is a resistance force.

How can a belt that is at rest in some inertial frame be turning those wheels? Because point contact cannot drive a wheel! Logic dictates then that the belt must be making more than point contact.

That means the belt must deform to the same shape as the wheel, at least where the belt and wheel meet. The belt must curve into a small arc at the bottom of the wheel. That curvature travels through circular motion, same as the bottom of the turning wheel. You will try and scoff at this, but it must be true because, once again, point contact cannot turn a wheel.

The point of all of this is this: The only part of the belt that matters to the cart is where the wheels touch the belt, and where the wheels touch the belt, the belt is formed into small arcs which are in circular motion, same  as the wheels are in circular motion. There is no inertial reference frame where this circular motion stops, as evidenced by the wheels are turning in all inertial frames. Simply put, those little arcs of belt are in circular motion and are driving the wheels in all inertial frames. There is no inertial frame, even the one where the top surface of the belt is at rest, where the belt is not driving the wheels. The belt is always driving the wheels and the treadmill cart has nothing to do with wind or wind energy.

If you want to claim the treadmill cart is going faster than the wind, that’s fine with me! I can wind up the spring on a little toy car and it will also go faster than the “wind” (the air in the room).

Neither the treadmill car nor the spring-powered car have anything to do with wind or wind energy.

As I said before, how the cart advances should be thoroughly scientifically investigated before making claims that really do not make any sense. The claim being made for the treadmill car to be going faster than the wind means nothing since it has nothing to do with wind or wind energy.

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52 minutes ago, OceanBreeze said:

I know very well what wind and what Galilean relativity is. I am saying the cart on the treadmill is never powered by wind energy; all of the cart’s energy is coming from the moving belt, all the time.

Do you really not see the problem there?  Wind is the RELATIVE motion of air with respect to a surface (the belt in this case).  "Powered by the wind" means powered by that relative motion, which is exactly what happens for the cart (which would obviously not work if air and belt were at rest with respect to each other, for instance if the treadmill is off).

52 minutes ago, OceanBreeze said:

As I said before, how the cart advances should be thoroughly scientifically investigated before making claims that really do not make any sense. The claim being made for the treadmill car to be going faster than the wind means nothing since it has nothing to do with wind or wind energy.

Imagine a huge treadmill inside a giant wind tunnel, so wide and long you can't see the edges or ends of it.  By Galilean invariance there is no experiment that can distinguish between that treadmill belt moving and the air at rest, or the belt at rest and the air moving. 

Therefore if the cart can advance up the treadmill belt, it can also advance ddw faster than the wind.  If not, that's an experiment that can distinguish these two scenarios, and that is impossible by Galilean invariance.  (The cart was tested on a small treadmill, but I assume you're not going to claim the results would be different on a large treadmill?)

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4 hours ago, OceanBreeze said:

I know very well what wind and what Galilean relativity is.

You say this, but it's inconsistent with your position that "Neither the treadmill car ... have anything to do with wind or wind energy." 

Wind is the relative motion between air and surface, and since the propcart is powered by this relative motion, without it, it would not move. I agree that this should be scientifically investigated as with all physics and engineering claims, and you can investigate this by removing the wind, by...

- turning off the treadmill, or

- running the treadmill in a vacuum chamber, or

- removing the prop from the cart

... and in all of these instances, the cart should still advance up the belt if it is not powered by the wind. Do you think it would advance up the belt? One of these setups is not very practical, while the other two are extremely easy, and have indeed been performed many many times with the result that the cart does not go.

(As far as material deformation and contact area effecting friction goes, you're right that it does. Diamond on diamond would be far less effective than say, plastic on rubber, or rubber on dirt, or what have you. But none of this has anything to do with which thing is moving, they would all succeed or fail in providing enough friction regardless.)

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4 hours ago, truthseeker said:

 

Therefore if the cart can advance up the treadmill belt, it can also advance ddw faster than the wind.  

One epiphany of sorts that I had last year when I was considering a different (but related) problem, is that the wind over a treadmill isn't similar, or equivalent, or representative of, or tantamount to, or any other adjective that relates it to the wind over the ground. It fully and literally IS the self-same thing, in any physically meaningful sense, since Michelson and Morley.

 

So to quibble on the second part of your sentence (and I know you already think this, but, you know, quibble) it should say "it is," not "it can also."

Edited by EfisCompMon
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5 hours ago, truthseeker said:

Do you really not see the problem there?  Wind is the RELATIVE motion of air with respect to a surface (the belt in this case).  "Powered by the wind" means powered by that relative motion, which is exactly what happens for the cart (which would obviously not work if air and belt were at rest with respect to each other, for instance if the treadmill is off).

What sort of relative wind does the moving belt produce? At best, there is a small disturbance of the air right at belt level. There is no wind tunnel being used with the small cart on the treadmill, just the belt. Again, since the cart is never moving with the belt, in the direction of the belt, it never encounters any relative wind. The cart that is advancing is outrunning no wind since no relative wind exists for that cart except the relative headwind. No wind or wind power is involved in that cart advancing any more than there is with the small wind up spring-powered car I mentioned. All there is, is the belt driving the wheels. You can imagine all the relative tail wind you like, but in reality, there is none ever involved with the cart. You are basically talking about outrunning an imaginary tail wind.

Of course, the cart requires air to advance since it has to develop prop thrust. Is the prop thrust now to be considered wind?  I suppose in some sense it is, but prop thrust is not a source of energy for the cart; the cart needs energy to produce the prop thrust and that energy all comes from the belt.

Quote

 

Imagine a huge treadmill inside a giant wind tunnel, so wide and long you can't see the edges or ends of it.  By Galilean invariance there is no experiment that can distinguish between that treadmill belt moving and the air at rest, or the belt at rest and the air moving. 

Therefore if the cart can advance up the treadmill belt, it can also advance ddw faster than the wind.  If not, that's an experiment that can distinguish these two scenarios, and that is impossible by Galilean invariance.  (The cart was tested on a small treadmill, but I assume you're not going to claim the results would be different on a large treadmill?)

 

That is a different experiment! There is no wind tunnel being used with the small cart on the treadmill. Why bring up a different experiment to back your claim?

 

(Sorry, I am at work and don't have time to reply more today)

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2 hours ago, OceanBreeze said:

What sort of relative wind does the moving belt produce?

It produces the relative motion between the air and the surface (i.e, the "wind"). (He said this in the post you were quoting: "Wind is the RELATIVE motion of air with respect to a surface (the belt in this case).") The relative motion between the air and the vehicle can be positive, zero, or negative, and the vehicle can accelerate (as evidenced in the videos) in all 3 of those conditions as long as the wind (air vs surface) is present.

Quote

That is a different experiment! There is no wind tunnel being used with the small cart on the treadmill. Why bring up a different experiment to back your claim?

I'm not sure he expressed himself well, it took me 2 or 3 read-throughs. What he meant was this: in one situation the wind tunnel is on, and the treadmill is off. In the other, the wind tunnel is off and the treadmill is on. There is no possible experiment that can distinguish which situation it is installed in. The results are guaranteed to be the same.

 

Edited by EfisCompMon
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2 hours ago, OceanBreeze said:

What sort of relative wind does the moving belt produce?

What part of "wind is the relative motion of air over a surface" are you having trouble grasping?  When you ride a long moving walkway you feel a wind in your face (which for the cart would be a tailwind, since it faces up the belt).  If you imagine that walkway is really wide as well as really long, you'd have no way of knowing if it's the belt that's moving and the air that's at rest, or the air that's moving and the belt that's at rest.  The two are equivalent by a Galilean transform.

2 hours ago, OceanBreeze said:

At best, there is a small disturbance of the air right at belt level.

You really can't get your head around Galilean transforms, can you?  You're completely stuck in the frame where the air is at rest.

2 hours ago, OceanBreeze said:

Again, since the cart is never moving with the belt, in the direction of the belt, it never encounters any relative wind.

Again, that's simply not true.  If you like you can start with the cart moving with the belt and watch it self-start until it's going up-belt.  

2 hours ago, OceanBreeze said:

That is a different experiment! There is no wind tunnel being used with the small cart on the treadmill. Why bring up a different experiment to back your claim?

Again - if the belt is really big, you cannot distinguish between a "real wind" - air moving and belt at rest, where for instance the air motion is produced by a fan and the belt is off - and "belt wind" - where the air is not moving but the belt is.  You cannot distinguish by any experiment because they are Galilean equivalent.  Since we know the cart advances up the belt in the latter scenario, we therefore know it will advance downwind faster than the wind in the former.

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10 hours ago, OceanBreeze said:

I know very well what wind and what Galilean relativity is. I am saying the cart on the treadmill is never powered by wind energy; all of the cart’s energy is coming from the moving belt, all the time.

Something else (it may sound like a quibble, but is actually important): The counterpart to "belt" is not "wind," it's "air." Depending on the frame of reference, the belt may be stationary or moving, and the air may be stationary or moving. But "wind" is unlike either of these 2 things, it's the relative motion between them both. Remove one or the other, and the wind disappears regardless of the velocity of the remaining belt/air. In all frames of reference, the wind (air vs belt) provides the energy.

The last part of this quote (after the semicolon, ending with "all the time") is not consistent with Galilean relativity. The cart's energy is coming from the moving belt, only in the frames in which the belt is moving. Likewise, the cart's energy is coming from the moving air, only in the frames in which the air is moving. But neither of these are "all the time" (if by "all the time" you mean "all the frames.")

(You can substitute "ground" or "surface" for "belt" into this post, and everything holds.)

Edited by EfisCompMon
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On 1/25/2022 at 4:20 AM, OceanBreeze said:

I know very well what wind and what Galilean relativity is. I am saying the cart on the treadmill is never powered by wind energy; all of the cart’s energy is coming from the moving belt, all the time.

Nope.  No power is available if the belt is moving the same speed as the wind.  The only time power is available is if there is a difference in the two, and (the important part) that difference in speed is harnessed to produce power.  Take away either and the cart just sits there.

Edited by billvon
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21 hours ago, truthseeker said:

What part of "wind is the relative motion of air over a surface" are you having trouble grasping?  When you ride a long moving walkway you feel a wind in your face (which for the cart would be a tailwind, since it faces up the belt).  If you imagine that walkway is really wide as well as really long, you'd have no way of knowing if it's the belt that's moving and the air that's at rest, or the air that's moving and the belt that's at rest.  The two are equivalent by a Galilean transform.

You really can't get your head around Galilean transforms, can you?  You're completely stuck in the frame where the air is at rest.

Again, that's simply not true.  If you like you can start with the cart moving with the belt and watch it self-start until it's going up-belt.  

Again - if the belt is really big, you cannot distinguish between a "real wind" - air moving and belt at rest, where for instance the air motion is produced by a fan and the belt is off - and "belt wind" - where the air is not moving but the belt is.  You cannot distinguish by any experiment because they are Galilean equivalent.  Since we know the cart advances up the belt in the latter scenario, we therefore know it will advance downwind faster than the wind in the former.

Don't keep telling me what a GT is. I know damn well what it is and how and why it is used. 

You don't seem to understand that there is NEVER any relative tailwind for the cart because it is held on the belt and started in still air.

The only wind the cart ever sees is a relative headwind when it starts to advance.

You say you can place the cart at the front of the belt and it will go back with the belt and it will self start? I call bullshit on this. I have looked to find evidence of this and all I found were people making excuses about why this does not work, such as "the belt is not long enough". So I would like you to back up this claim and show me a video of the cart self-starting in this scenario. I predict the cart will fall off the back of the belt! The only way these carts can start on the treadmill is to be held down on the belt until the prop winds up enough to produce thrust, then it is released.

When you say the cart is going faster than the wind, you are in effect saying it is outrunning an imaginary tailwind. It is exactly the same as a small wind up toy car running on the floor. It too is running faster than an imaginary wind.

This entire claim is based on bollocks!

Edited by OceanBreeze
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