Merged DDWFTTW in a “Real” Wind

[Jack by the hedge]

Yes indeed. Two different scenarios.

 

[Jack by the hedge]

I wondered why, when the spool of thread drops on the floor and rolls underneath the couch, it never comes out when you pull on it! You just get a lot more loose thread, and have to poke it out with a stick.

Sometimes it does come out. Other times it snags on something and the reel just spins in the same spot, paying out more thread. It's not particularly mysterious.

 

[spork]

It's not particularly mysterious.

To be fair, you have to consider the other experiments he's done. We're not talking about a Nobel Laureate here.

 

[phunk]

Try it with a large reel, long thread. The reel will dance about, as it trails behind you. Average speed, your speed.

Just pulled a reel about 30ft with no slipping, dancing about, or slack in the line. Only had to move the string about 5 feet.

 

[humber]

wrong.

It has to do with the ratio of the two parts of the reel. It will be difficult to make a full reel move towards the hand. It is, as I Ratant has noted, often hard to retrieve one that has rolled away. Friction can overcome the advantage of the gearing. If rolling forward involves more work because of that friction, it will roll the other way. Principle of least action.

 

[Myriad]

Sometimes it does come out. Other times it snags on something and the reel just spins in the same spot, paying out more thread. It's not particularly mysterious.

Or the spool lands with the thread paying out at the top. Or the spool is end-on to the direction you're pulling the thread. Or the spool is fully wound leaving very narrow flanges. Or the spool lands resting on one end. Or...

Respectfully,
Myriad

 

[humber]

Just pulled a reel about 30ft with no slipping, dancing about, or slack in the line. Only had to move the string about 5 feet.

And is the reel gaining on your hand? Then it's accelerating isn't it?
You are confusing a change on closing distance with speed.
You are simply applying more work, because compared to your resources, the work on the reel is trivial. The wind is limited, and a large reel or cart will make demands that will exhaust it.

 

[spork]

It has to do with the ratio of the two parts of the reel. It will be difficult to make a full reel move towards the hand. It is, as I Ratant has noted, often hard to retrieve one that has rolled away. Friction can overcome the advantage of the gearing. If rolling forward involves more work because of that friction, it will roll the other way. Principle of least action.

Classic humber! I always love how he tries to explain trivial matters to people after he's gotten it horribly wrong for so long.

 

[CORed]

I look forward to the games humber will play with the data that I made available to him through NALSA - the data that he claims I will not let anyone see. Data that I have never once protected.

He'll have an absolute blast making up lies with data that he could never begin to understand.

Now that's the right attitude. It's best not to let humber get you angry. Hell, he gets me angry sometimes, and it's not my accomplishments he's calling fraudulent. Nonetheless, humber can turn me into the guy in the XKCD cartoon, who's sitting in front of his computer saying, "I can't come to bed yet honey. Someone on the internet is wrong".

For you it's personal, so I'm sure it's much more difficult to keep a sense of perspective. You've done something akin to climbing Mount Everest. It's impressive, it took a lot of work, but, in the grand scheme of things, not all that useful. But then you've got humber over there saying, "You didn't really climb mount Everest, I saw a Yeti pushing you the whole way."

But you've got to realize, anybody who knows their burro from a burrow can tell that humber's FOS.

 

[humber]

Classic humber! I always love how he tries to explain trivial matters to people after he's gotten it horribly wrong for so long.

If when in a car traveling at 10mph, there is a car to the rear traveling at 20mph, you would expect that at sometime that car will overtake you.
Slow walking pace is about 3mph. If the pulled reel is traveling at 6mph, then from the length of thread, it is a quick calculation to determine when it should overtake you. I doubt that will happen, but also wonder how I can still pull it, should it do so. Thread is not wind, Chief. It has the properties of a thread.

 

[I Ratant]

Or the spool lands with the thread paying out at the top. Or the spool is end-on to the direction you're pulling the thread. Or the spool is fully wound leaving very narrow flanges. Or the spool lands resting on one end. Or...

Respectfully,
Myriad

.
Loose spools of thread work in mysterious ways.
Rigorous test protocols eliminate the random variables.

 

[humber]

Now that's the right attitude. It's best not to let humber get you angry. Hell, he gets me angry sometimes, and it's not my accomplishments he's calling fraudulent. Nonetheless, humber can turn me into the guy in the XKCD cartoon, who's sitting in front of his computer saying, "I can't come to bed yet honey. Someone on the internet is wrong".

For you it's personal, so I'm sure it's much more difficult to keep a sense of perspective. You've done something akin to climbing Mount Everest. It's impressive, it took a lot of work, but, in the grand scheme of things, not all that useful. But then you've got humber over there saying, "You didn't really climb mount Everest, I saw a Yeti pushing you the whole way."

But you've got to realize, anybody who knows their burro from a burrow can tell that humber's FOS.

Wait until I get the data. Mt Everest? More like an over inflated castle.
Cotton reels that travel twice the speed of the hand that is pulling them

 

[spork]

.
Loose spools of thread work in mysterious ways.

Yes - mysterious to my dog perhaps.

Rigorous test protocols eliminate the random variables.

Splendid - you're doing the lords work. Not the silly, pointless sort of thing you insist on insulting us over. You must be very proud.

Next... a ball of yarn.

 

[CORed]

Wait until I get the data. Mt Everest? More like an over inflated castle.
Cotton reels that travel twice the speed of the hand that is pulling them

See spork: You're going to be debunked by somebody who can't understand a cotton reel.

 

[humber]

.
Loose spools of thread work in mysterious ways.
Rigorous test protocols eliminate the random variables.

Inner 3", outer 9" circumference.
Simple rule:
Over
Reel moves 9" (one turn)
Hand moves 9 + 3 = 12"

Under
Reel moves 9" (one turn)
Hand moves 9 - 3 = 6"

"Half the speed"
But, that can only happen if there is enough thread between the reel and the hand to avoid the hand and reel coming in contact.

Work = F*d, so the same in each case
12*F = 6*2F
The under version requires twice the force.

But F=ma, so acceleration is doubled in the under case.
Now there is a need to consider time, and not just distance.

 

[humber]

See spork: You're going to be debunked by somebody who can't understand a cotton reel.

You can count on it.

 

[CORed]

You can count on it.

I'm sure you will come up with a whole lot of nonsense that you and only you think debunks ddwftw, but really makes no sense at all.


Something like your stored angular momentum explanation for the treadmill.

 

[phunk]

And is the reel gaining on your hand? Then it's accelerating isn't it?

No, not accelerating. It's traveling at a fixed* multiple of the string speed.

You are confusing a change on closing distance with speed.

Wrong, I'm comparing speed of the string and the speed of the spool, both relative to the ground.

You are simply applying more work, because compared to your resources, the work on the reel is trivial. The wind is limited, and a large reel or cart will make demands that will exhaust it.

The amount of work isn't what we're arguing about here, we're arguing about speed relative to the ground and the wind. There isn't a fixed amount of work that can be done for any given wind speed. I could always change the size of the sail to get more or less energy from the wind, right? Or sail at a different direction to the wind to get more or less work from the same wind, right? Or have the sail rotate perpendicular to the wind, so that it's extracting energy from the wind as if it was on a reach, when it's actually moving downwind...



*changing slightly as the radius of the wound string increases, but this is not necessary to achieve the effect.

 

[Michael C]

Of course it isn't necessary to have string winding onto the reel. Here's a little question for a physics test:

A cotton reel rests on a level surface. The radius of the cotton reel at both ends is b and the radius at its narrowest part is a. A thin strip of cardboard is placed under the centre of the cotton wheel so that it touches it at the narrowest part. Assuming that there is sufficient friction between reel and surface and between reel and cardboard to prevent any slippage, what is the velocity of the cotton reel if the strip of cardboard is moved to the right at velocity v?

 

[humber]

No, not accelerating. It's traveling at a fixed* multiple of the string speed.
Wrong, I'm comparing speed of the string and the speed of the spool, both relative to the ground.
*changing slightly as the radius of the wound string increases, but this is not necessary to achieve the effect.

Sounds like you are fixated with the ground...
Or was simply that the best choice, unless told "that's what most people do"?

The amount of work isn't what we're arguing about here, we're arguing about speed relative to the ground and the wind.

Terminal velocity is limited by power = Work/time.

There isn't a fixed amount of work that can be done for any given wind speed.

There certainly is.

I could always change the size of the sail to get more or less energy from the wind, right?

Then to win the a race, use a bigger sail than anyone else?
How do you propose to get a faster than ddw sail?
The 2X cotton reel would overtake you, no matter what, and then you have a problem. I will now be behind you. What to do? Wait until it slows so that you may pull it again? Possible, but then over time, you will find that the average speed of the reel is the same as your speed. Transient behavior can be deceptive.

Or sail at a different direction to the wind to get more or less work from the same wind, right?

Tacking, you mean.
But didn't you just say work was not an issue?

Or have the sail rotate perpendicular to the wind, so that it's extracting energy from the wind as if it was on a reach, when it's actually moving downwind..

Tacking again.
A prop is a rotating airfoil, so it may be expected to work as a sail. Its motion allows it to move away from the air that has been slowed by driving it, and into fresh air. Its construction and design allow for high L/D ratios. All good.
It may therefore be said to be "efficient", but that comes at price.

Although the disk area may be 20 sq. meters, that is not the same as 20 sq. meters of sail. At any instant, there is only the area of the blades themselves, but a sail has the entire area 24/7. More efficient in one sense, but extracts less energy in total. Less powerful than a sail.

Get a big reel and see if you can get it to travel twice as fast as you walk.
It may appear to, while accelerating, but after that it won't.