Merged DDWFTTW in a “Real” Wind

[windgrins]

A case in point

Mostly he just strings together random bits of technical sounding gibberish, sometimes sprinkling in some mathematical or pseudo-mathematical formulas, (in at least once case, the "formula" had no "=" or inequality), then claims it supports his position. Often, if it means anything at all, it actually refutes his position.

Yes over at Talk Rational, he was having a argument with Uncool about how velocity doesn't change for an object because you change Reference Frames and he quoted a web site to tell Uncool about speed and velocity which had the following statement in it:

"As a position vector itself is frame dependent, velocity is also dependent on the reference frame."

He either doesn't even read the stuff he copies or is oblivious to the fact that it contradicts the very point he's trying to make.

Then he wonders why no one is taking him seriously!

Regards,

WindGrins

 

[jadebox]

Even what *you* might consider to be a simple explanation much still be correct to be of much value.

What I said was correct.

Completely wrong. The movement of the air relative to the ground is *exactly what's important* from the viewpoint of the cart -- exploiting that relative movement is the ONLY way the cart can travel DDWFTTW

What I said was right. You're mixing two reference points, "the movement of the air relative to the ground" and "from the viewpoint of the cart" in one statement. I was looking at things just from the viewpoint of the cart. To the cart, the ground is moving underneath it. It doesn't care if that was caused by "the wind" or by "a treadmill."

Nope - it's *all* important to the cart. You can't say that the pistons are more important that the driveshaft in the family car. Take either one away and you're done. It's a package deal.

I didn't say anything like that.

Not relative to the ground it can't be. If that statement were true, a PM machine would have been invented and it wasn't.

You took what I said out of context. I didn't say anything about a perpetual motion machine. I was describing the treadmill set up which is equivalent to the cart in the wind.

Nope, the treadmill does *not* illustrate a zero wind speed (relative to the ground) scenario.

I didn't say that it did.

The treadmill demonstrates a zero wind speed relative the the vehicle chassis scenario (and speeds just above and below that).

Yes, that's what I said.

-- Roger

 

[recursive prophet]

A: we weren't attempting to demonstrate DDWFTTW in that video.

If that test wasn’t to show ddwfttw, then what was it’s purpose?

I don't think I would be surprised. The BB started off very slow and took quite a bit of time to get from zero to WS. Over any reasonable distance a cart with a jibb could beat it from a standstill. That isn't the point. It isn't a sprinter. It is the top speed that is amazing about the BB, not how quick it is.

Hmm. What you say about the gearing resonates with my own understanding, but a question arises. Explain how the cart that jb videoed at the end of the great prop/turbine race- http://www.youtube.com/watch?v=r6c01c_BTLQ didn’t have enough time to really demonstrate fttw there when it can advance on the TM after being held down for just seconds. I was told very little KE was involved in that transfer, so what gives? If the TM is an instance of ddw.., how come it can exceed ws so quickly while the same cart on the ground can’t pull it off in several hundred feet? Same cart; same gearing, yes?

@I Ratant: Check your mail. I have some test suggestions I really hope you'll have time to indulge.

@Michael: I should have said toward the tailwind. As I mentioned in my last post I wasn't implying the ice boat sails weren't set at an angle to the wind. I'll have to give you thrust question more ponder time I guess, to learn why the angle helps the iceboat while slowing the cart. The more I look at mender's explanation the more rational it becomes.

 

[jadebox]

Yes, I'm clear on all that. It is obvious though where an aircraft gets its power to turn the prop and not so obvious where the cart gets its power. We say it gets its power from the wheels but there is more to it than this.

Yes.

The reason the wheels are not slowing the cart and using its KE is that the prop is providing thrust to push on the wheels-more than just is coming back to it through the feedback of the drivetrain. The prop's thrust would quickly diminish to 0 if there was not additional energy being imparted to the prop by the airmass/ground interface. The fact that the cart is being constrained from going forward by the wheel allows the relative wind on the prop to apply this additional force to drive the wheels. If the true wind did not exist, the prop would be producing thrust but slowing until the cart stopped. This additional energy that not only lets the cart continue to run but accelerate it past wind speed is what Ynot is looking for.

Yes, but my concern was that the talk about how the propeller runs into a headwind and of the propeller tacking and all that made the explanation more confusing.

It seems that most people understand, or at least accept, that the energy to accelerate the vehicle comes from the difference in speed between the ground and the wind. And they understand that a propeller can accelerate a vehicle. Neither of those things challenge our "common sense."

But they get stuck thinking about what happens when the cart reaches wind speed - as if there is some sort of transition that happens at that point. That's why I was suggesting that talking about the wind, and it's interaction with the propeller, just adds to the confusion. Using the cart on a treadmill example, and showing how the turning of the wheels drives the propeller is easy to understand.

-- Roger

 

[ThinAirDesigns]

If that test wasn’t to show ddwfttw, then what was it’s purpose?

You really expect me to believe that you don't know the purpose of the video in question when in the very next paragraph you write:

Explain how the cart that jb videoed at the end of the great prop/turbine race- http://www.youtube.com/watch?v=r6c01c_BTLQ ...

Got any other stupid questions that you directly proceed to answer yourself?

JB

ETA: for those that think I'm being harsh on RCP, you would need to know that this is the umpteenth time we've been through this with him. He's asked the same questions for years and isn't interested in listening to the most basic of answers.

 

[ThinAirDesigns]

If the TM is an instance of ddw.., how come it can exceed ws so quickly while the same cart on the ground can’t pull it off in several hundred feet? Same cart; same gearing, yes?

Oddly enough rolleyes:), a human pushing the device can get it up to speed quicker than the wind can. Ask humber about his -- he'll explain it to you.

JB

 

[windgrins]

Clearing up Treadmill misunderstanding!

If that test wasn’t to show ddwfttw, then what was it’s purpose?


Hmm. What you say about the gearing resonates with my own understanding, but a question arises. Explain how the cart that jb videoed at the end of the great prop/turbine race- http://www.youtube.com/watch?v=r6c01c_BTLQ didn’t have enough time to really demonstrate fttw there when it can advance on the TM after being held down for just seconds. I was told very little KE was involved in that transfer, so what gives? If the TM is an instance of ddw.., how come it can exceed ws so quickly while the same cart on the ground can’t pull it off in several hundred feet? Same cart; same gearing, yes?

@I Ratant: Check your mail. I have some test suggestions I really hope you'll have time to indulge.

RC

The answer to this one is pretty simple. For the treadmill test, the person's hand held the cart in position to get the wheels and prop spinning at treadmill speed. The cart did not have to get to WS by itself. It is the equivalent of using a V8 vehicle to tow the BB up to WS and then letting it accelerate on its own.

Notice that the carts on the treadmill did not accelerate lightning fast up the belt once released but does run up the belt. The BB doesn't either.

The little carts are have a higher thrust to weight ratio so they do accelerate better than BB.

So, if BB is towed to WS, in just a few seconds, it could demonstrate DDWFTTW also but this isn't what they are doing with the big carts. They are letting them self start and bring them selves up to wind speed.

This isn't done on the treadmill because the treadmill isn't long enough. The cart will fall off the back before it has a chance to get to WS. If you had a really long treadmill, like the ones at the airports, you could do the equivalent.

Does this clear this up for you?

Regards,

WindGrins

 

[Modified]

Explain how the cart that jb videoed at the end of the great prop/turbine race- http://www.youtube.com/watch?v=r6c01c_BTLQ didn’t have enough time to really demonstrate fttw there when it can advance on the TM after being held down for just seconds. I was told very little KE was involved in that transfer, so what gives? If the TM is an instance of ddw.., how come it can exceed ws so quickly while the same cart on the ground can’t pull it off in several hundred feet? Same cart; same gearing, yes?

Holding it down on the treadmill is equivalent to pushing it to wind speed. More precisely, it's like carrying it at wind speed then lowering it to the ground and pressing down until the wheels stop slipping.

 

[Michael C]

Hmm. What you say about the gearing resonates with my own understanding, but a question arises. Explain how the cart that jb videoed at the end of the great prop/turbine race- http://www.youtube.com/watch?v=r6c01c_BTLQ didn’t have enough time to really demonstrate fttw there when it can advance on the TM after being held down for just seconds. I was told very little KE was involved in that transfer, so what gives? If the TM is an instance of ddw.., how come it can exceed ws so quickly while the same cart on the ground can’t pull it off in several hundred feet? Same cart; same gearing, yes?

When the cart is placed on the treadmill, it is already running at the speed of the wind. On the road, the equivalent action to placing the cart on the treadmill would be this: hold the cart above the road already moving at wind speed (you'd need a vehicle moving at the same speed/direction as the wind) and place it on the road. When you place it on the road (or the treadmill), the wheels will immediately start turning and the prop will be turned by the wheels: as soon as the cart is placed on the belt it is moving at wind speed and the propeller is producing thrust (hey, by the way, what about having another go at my question about prop thrust?).

I see that while i was writing this reply, others have already said the same thing. Hope it helps!

 

[Dr. Keith]

If you had a really long treadmill, like the ones at the airports, you could do the equivalent.

Assuming the belt was fast enough to simulate the necessary WS.

 

[windgrins]

Agreed!

Yes.



Yes, but my concern was that the talk about how the propeller runs into a headwind and of the propeller tacking and all that made the explanation more confusing.

It seems that most people understand, or at least accept, that the energy to accelerate the vehicle comes from the difference in speed between the ground and the wind. And they understand that a propeller can accelerate a vehicle. Neither of those things challenge our "common sense."

But they get stuck thinking about what happens when the cart reaches wind speed - as if there is some sort of transition that happens at that point. That's why I was suggesting that talking about the wind, and it's interaction with the propeller, just adds to the confusion. Using the cart on a treadmill example, and showing how the turning of the wheels drives the propeller is easy to understand.

-- Roger

I agree that the first mystery for people is generally, how does it work at WS because there's "no wind"

But explaining how it works in general clears that up, as well as, how does it outrun the wind (or operate in its self generated headwind).

So we just approached this from two directions.

We would have to ask Ynot if either or both explanations were more or less helpful to the question he asked.

I would call this resolved. Amazing how a reasonable conversation can resolve ambiguity and come to a common understanding!

Regards,

WindGrins

 

[Dr. Keith]

Holding it down on the treadmill is equivalent to pushing it to wind speed. More precisely, it's like carrying it at wind speed then lowering it to the ground and pressing down until the wheels stop slipping.

Most concise answer, do we have prize?

 

[ThinAirDesigns]

@I Ratant: Check your mail. I have some test suggestions I really hope you'll have time to indulge.

I'm having visions of a handheld fan chasing popcorn strewn across the ground.

JB

 

[ThinAirDesigns]

Most concise answer, do we have prize?

The only prize would be given to the person to which that exact answer has been given scores of times over the last near 2 years and yet still can't remember it.

JB

 

[Dr. Keith]

The only prize would be given to the person to which that exact answer has been given scores of times over the last near 2 years and yet still can't remember it.

JB

No doubt. But for now he appears to be willing to learn, and my wisdom is not as deep as yours. I just recently gave up on humber, after all.

 

[windgrins]

Big Clue here for RP!

Assuming the belt was fast enough to simulate the necessary WS.

Agreed.

RP, notice that three different posters, with no knowledge of the other's answers all answered your question with fundamentally the same info.

This should give you an idea about the poster's knowledge of physics with regards to some other poster(s) on this blog!

Regards,

WindGrins

 

[jadebox]

We would have to ask Ynot if either or both explanations were more or less helpful to the question he asked.

If we didn't scare him away ....

-- Roger

 

[ThinAirDesigns]

What I said was correct.



What I said was right. You're mixing two reference points, "the movement of the air relative to the ground" and "from the viewpoint of the cart" in one statement. I was looking at things just from the viewpoint of the cart. To the cart, the ground is moving underneath it. It doesn't care if that was caused by "the wind" or by "a treadmill."



I didn't say anything like that.



You took what I said out of context. I didn't say anything about a perpetual motion machine. I was describing the treadmill set up which is equivalent to the cart in the wind.



I didn't say that it did.



Yes, that's what I said.

-- Roger

What you have said are a whole series of statement where to make them "correct" or close to correct, you must switch reference frames between them. If you don't tell the reader you are switching frames or definitions in the middle of your description, they will easily assume that you have not.

JB

 

[ThinAirDesigns]

No doubt. But for now he appears to be willing to learn, and my wisdom is not as deep as yours. I just recently gave up on humber, after all.

This is the advantage that those here with two years of RCP history have over the newer participants.

I have no quarrel whatsoever with your position -- just letting you know that he is no more willing to learn than is Humber. His ignorance is willful and his only interest is to enjoy the **** he stirs.

JB

 

[A.T.]

I still think that talking about wind tends to confuses the issue.

Only if you fail to define what you mean by "wind" or even worse: use that word interchangeably for different things:

The cart is moving with the wind. You can think of it as a part of the wind.

Here "wind" apparently means "airmass"

The "wind" - relative to the ground

Here "wind" apparently means "movement of the airmass"

The wind speed could be zero, but if the ground were moving backwards relative to the cart, the propeller would spin and the cart would be accelerated. The treadmill test illustrates this.

Here "wind" apparently means "movement of the air relative to the cart"

the energy to accelerate the vehicle comes from the difference in speed between the ground and the wind.

Here "wind" apparently means "airmass" again

That's why I was suggesting that talking about the wind, and it's interaction with the propeller, just adds to the confusion.

I think that inconsistent terminology add the most confusion in communication.

Using the cart on a treadmill example, and showing how the turning of the wheels drives the propeller is easy to understand.

Experience shows otherwise. The treadmill seems very difficult to understand to laymen, and even to physics professors from liberal art colleges.