Merged DDWFTTW in a “Real” Wind

[humber]

A balloon, suspended in a body of air, accelerates in the direction which the ground is moving relative to the air, despite there being no interaction between the air around the balloon and the ground. Please explain.

Sure. There may be a fight in a bar, but if you don't get punched, or do the punching, you are not in it.
The balloon accelerates relative to the air. The ground has nothing to do with that, no matter which way it is "going". No force, no action.
However, if you want the information, about the speed of the air or object relative to the ground, then you may measure it from the ground. And?

 

[humber]

mmm...

 

[CORed]

Any book on general fluid dynamics, will contain the theory that says that objects do not travel at the speed of the medium.

You won't find an example of where a text says that they balloons do, because of the above fact. You also won't find one where they don't say that balloons don't, because of the above the first statement.

In short, a text book from may give an example of where a brick falls to the Earth, but that does not mean that because it was not specifically mentioned, that an i-pad, won't.

Folks, this is what happens when you arrogantly try to pass yourself off as an expert on a topic about which you don't know a whole lot, and stubbornly refuse to admit to an error. Take this example to heart, and try not to let it happen to you.

 

[temporalillusion]

mmm...

(stage whisper)

Your "wind must travel faster" idea of what creates lift is wrong, everyone's looking.

 

[ThinAirDesigns]

Gee, I wonder why?

Exactly -- because is saves them from having to admit they ********** up.

JB

 

[Subduction Zone]

I still want to know why humber believes this nonsense. The balloon is not in contact with anything except the air it's suspended in. If it is released while travelling faster than the air, why would it slow down to less than the speed of the air? Consider the moment the balloon was travelling at windspeed: what force would make its velocity continue to change?

I think you are starting to see how humberphysics can be so interesting.

 

[humber]

Folks, this is what happens when you arrogantly try to pass yourself off as an expert on a topic about which you don't know a whole lot, and stubbornly refuse to admit to an error. Take this example to heart, and try not to let it happen to you.

Uh huh. But you don't mind pushing your opinion as fact, though it has no theoretical or direct and published support?
If not from those putative sources, where did the ideas you hold come from, and how many of them did you hold to before becoming a cart supporter?

 

[humber]

Exactly -- because is saves them from having to admit they ********** up.

JB

Pure speculation, but your own street video demonstrates you were in that state, because the damn ornery thing didn't work.

 

[humber]

(stage whisper)

Your "wind must travel faster" idea of what creates lift is wrong, everyone's looking.

...didn't say that, but that the wind speeds must be different. As a result, I expect that the experience of "zero wind" to be quite common when ballooning.

 

[CORed]

Uh huh. But you don't mind pushing your opinion as fact, though it has no theoretical or direct and published support?
If not from those putative sources, where did the ideas you hold come from, and how many of them did you hold to before becoming a cart supporter?

Most, if not all of the "opinions" I state are obvious to anybody with a rudimentary knowledge of physics. I learned it in high school and college courses, and independent reading. I became a "cart supporter" because it was clear to me that though the design was non-obvious (to me anyway) there was absolutely no reason it couldn't work.

Also, Spork and JB were clearly not hiding anything. They gave detailed instructions on how to replicate their treadmill tests, and others confirmed their results.

OTOH, you, while trying to pass yourself off as some kind of expert, made an incredible string of laughable, fundamental errors that made it clear that you were either deliberately spouting nonsense to yank our chains, or that you had no idea what you were talking about, starting with your dismissal of the validity of the treadmill test.

 

[spork]

To be fair, the context was a red herring raised by humber of a positively buoyant hot air balloon.

I would claim that a positively buoyant hot air balloon LOSES potential energy as it ascends - just as a rock loses P.E. as it falls.

I became a "cart supporter" because it was clear to me that though the design was non-obvious (to me anyway) there was absolutely no reason it couldn't work.

Also, Spork and JB were clearly not hiding anything. They gave detailed instructions on how to replicate their treadmill tests, and others confirmed their results.

JB and I have tried to be completely open with our designs, test procedures, data, and results. You'll find most of our mistakes described on our blog without shame (it was our first 450 lb, 23' tall, manned DDWFTTW cart - we made few mistakes).

We kind of like the fact that most people that allow themselves to get dragged into this wind up being convinced, either by the explanations, the real-world evidence, or simply the fact that we try to be as open with the facts as we know how. Yes, there have been plenty of attacks and insults thrown our way, and we don't always (ever?) rise above it. We're human (barely). To the best of my knowledge, no one has ever started out believing DDWFTTW is possible and been convinced differently - but many have made the opposite transition.

I think one of the great shames is that people with a genuine curiosity about this and related topics wouldn't come within a mile of these forums because of the ridiculous trolls and ensuing drama. It's astonishing how different the reception is in real life.

I appreciate everyone that's supported or even tolerated us and our project.

 

[zooterkin]

Not so sure about that. When the balloon is neutrally buoyant I don't think it's quite accurate to say it's gained potential energy by moving to higher altitude.

Puncture the balloon, and I think you'll find the potential energy gets released.

 

[zooterkin]

Newton says that F should be opposed by an equal force. That part of the equation is missing. That opposing force is not just due to the acceleration of the balloon, its inertia, F=ma, but drag components as the air flows over the balloon. Contact of the wind, with the balloon slows it, and it builds up in front of the balloon, as well as all sorts of parasitic drag effects. The balloon can never get to the state where (Vwind - VBalloon)^2. Simple as that.

Never? Really? What happens when the wind speed is zero; what velocity is the balloon moving with then?

ETA: I suspect you're talking nonsense with respect to the formulae, but the question still remains; if you insist the balloon must be travelling at a different speed from the air around it, what happens if there is no movement of the air?

It's vaguely true that at wind speed, in a hot air balloon, there may be no wind on your face, but above your head, is an enormous balloon. The basket hangs below the center of the balloon. The wind that may pass directly by you by in the basket, has to go all the way around the balloon up above and in in the same time. How does that happen if the wind in your face is the same speed as the wind going around the balloon?

If the balloon is moving at the same speed as the air around it, what wind is there to pass around the balloon? You do understand what wind is, don't you?

 

[zooterkin]

I would claim that a positively buoyant hot air balloon LOSES potential energy as it ascends - just as a rock loses P.E. as it falls.

You seem to be channelling humber now. If there's a rock in the basket of the hot air balloon, is that rock gaining or losing potential energy as the balloon rises?

ETA: Actually, I think I can see what you're getting at, but I think you're ignoring things like the energy being put into the system by heating the air, for example.

 

[spork]

Puncture the balloon, and I think you'll find the potential energy gets released.

I think you'll have to define what a "neutrally buoyant balloon" is. When you puncture it, you'll find that the envelope falls and the contents rise.

 

[EHocking]

I'm speechless.

yes, it's difficult to remain lurking with this stuff flying about.

I hope you didn't miss the posts where the heat source on a hot-air balloon is an engine and the other howler that an internal-combustion engine is a heat engine.

 

[zooterkin]

I think you'll have to define what a "neutrally buoyant balloon" is. When you puncture it, you'll find that the envelope falls and the contents rise.

Or, since we're talking about a hot-air balloon, just turn off the burner and wait. I'm willing to be convinced by figures, but I don't think it's as simple as because it is rising, it is losing potential energy. It's also gaining PE due to its height, and also losing the potential energy from the fuel being burnt. I think it depends which parts you're going to include whether a rising balloon is gaining or losing potential energy.

 

[humber]

I would claim that a positively buoyant hot air balloon LOSES potential energy as it ascends - just as a rock loses P.E. as it falls.

When an object falls, its gravitational potential energy becomes kinetic energy. If there are no losses to drag, then just before the object hits the ground, 100% of the potential energy has been transferred as kinetic energy.
Parachutists avoid that fate, by using the drag of the chute to dissipate the potential energy, so minimizing their kinetic energy upon landing.

There is no such thing as single "neutrally buoyant" balloon. That NB state can be achieved by a wide range of volumes, structures and gas densities. I offer The Hindenburg as an example or what is possible.

JB and I have tried to be completely open with our designs, test procedures, data, and results. You'll find most of our mistakes described on our blog without shame (it was our first 450 lb, 23' tall, manned DDWFTTW cart - we made few mistakes).

As if. The dyno was supposed to measure wheel force and prop thrust. However, and without notice, that became some Rube Goldstein contraption, tied to a truck, where success was apparently measured by how much the rig "walked" due to vibration, upon the small pegs supported my smooth plates.
The cart's weight changes like a yo-yo, the gearing ratio selected by trial and error, ratchets set this way and that, and the rules for the trial were last revised on July 3rd. The last day of the trial. Not to mention that until the official trail, windspeed was not measured at all, and indication was by pon-pons from Staples.

We kind of like the fact that most people that allow themselves to get dragged into this wind up being convinced, either by the explanations, the real-world evidence, or simply the fact that we try to be as open with the facts as we know how. Yes, there have been plenty of attacks and insults thrown our way, and we don't always (ever?) rise above it. We're human (barely). To the best of my knowledge, no one has ever started out believing DDWFTTW is possible and been convinced differently - but many have made the opposite transition.

That self-serving emphasis on belief and being convinced, tells of your motives. Science does not work that way, but game shows and Oprah, do.

I think one of the great shames is that people with a genuine curiosity about this and related topics wouldn't come within a mile of these forums because of the ridiculous trolls and ensuing drama. It's astonishing how different the reception is in real life.

Not to mention your physics.

 

[humber]

Or, since we're talking about a hot-air balloon, just turn off the burner and wait. I'm willing to be convinced by figures, but I don't think it's as simple as because it is rising, it is losing potential energy.

It gains PE by rising.

It's also gaining PE due to its height, and also losing the potential energy from the fuel being burnt.

Depends on what you mean. The system loses energy to heat, but the mass of the unburned fuel gains energy as PE when the balloon rises.
The heat is used to change the air density, and it is the displacement of the colder denser air, that results in the balloon's rise. No different from floating in a bath.

 

[humber]

yes, it's difficult to remain lurking with this stuff flying about.

I hope you didn't miss the posts where the heat source on a hot-air balloon is an engine and the other howler that an internal-combustion engine is a heat engine.

An internal combustion engine is a heat engine. The transfer of heat of combustion to mechanical work, is done at the piston, rather than externally as with a hot air balloon.