Down wind faster than the wind

[ThinAirDesigns]

See what you've done there? You've avoided mentioning that a gyro compass will give me my velocity wrt the ground. Not to mention the accelerometer.

He avoided mentioning them because neither are true.

Both a gyro and a accelerometer only react to changes -- and changes aren't applicable to a steady state test.

Keep waiting for that change -- the very definition of 'steady state' means that the change you wait for isn't coming.

JB

 

[Dan O.]

Of course, for relative novices like myself, there are interesting questions that we could discuss, about how the force acts on a sphere or wheel to both give it angular momentum and how some of that ends up accelerating the centre of gravity as well. This last part is why, of course, the orange, pool balls, cherries, 'un-prop-ed' cart, or indeed ynot's glass marble on a turntable, etc., do not manage to keep up. Some guys round here, I'm farily sure, would be able to tell us how the force is translated into rotation vs acceleration with the surface.

I would be more likley to ask you to figure it out for yourself with some helpfull guidance. You would start by diagraming all the forces involved. Gravity and the normal force from the table cancel and can be ignored for now. The force from traction, the linear inertial force the torque and the angular inertial force all have to balance so it's just a little bit of algebra to find the answer. [Hint: if you are not up to calculating the moment of inertia for simple geometries you could just look it up in the list of moments of inertia^WP ]

This isn't off-topic since it is preliminary to doing the calculations for the ddwfttw cart.

 

[mender]

Speaking of predictions, is there enough information to predict a final speed in a 10 mph wind based on the advance ratio and the break-even speed as shown on the treadmill?

The small cart has a break-even speed of 2.7 mph and has a .8 advance ratio. The amount of force needed (momentum change of the affected air) for this particular configuration and propeller size is given by the break-even speed.

Any thoughts?

 

[humber]

Humber, this isn't freefall terminal velocity, where the air resistance builds up over time to match the force of gravity, in which case you'd be more or less correct.

CORed was discussing a much different type of scenario, where the primary motive force is a tailwind, in which case, the force on the parachute or umbrella actually is at a minimum at maximum velocity.

Yes, that's called a straw man. If you are dragged by the belt, you get a headwind, not a tailwind. The "way" I am facing is not at all important. All velocities are 'relative', right?
Not important though, I can take your stance.
Attach a spring balance to an object and drag it through a trough of light oil, until the object moves at 3m/s. Put that same object in a trough of oil flowing at 10m/s. Follow the object it until it reaches its maximum velocity, say, 7m/s. How much force will it take to get it to 10m/s? None? Is that what you say? Where does that come from if needed?
How is it then, when traveling from going back with the belt to stationary, the force alwaysfalls until 'winspeed' is reached?
On the treadmill, the final force is only the friction to the belt, and not the force maintaining an object at windspeed.

[/QUOTE]
Consider the following scenario:

You're standing still on ice, with ice skates. You are topless.

On the middle of your back is a ripe pimple, ready to explode.

A strong wind develops and pushes you forward (so the wind is pushing against the pimple).

You accelerate, due to this force, until your forward velocity matches that of the wind. At that point, you cease to accelerate, and maintain a steady velocity.

Question: when is the pimple more likely to pop?

You contend that since forces are maximized at maximum velocity, it would be more likely to pop at this maximum velocity.

We contend that it would be more likely to pop the moment the wind develops, since the unbalanced force of the wind is at a maximum at that moment in time.


Now, if you had a pimple on your chest, and there was air resistance to factor in, then yes the chest pimple would be more likely to pop at maximum velocity.

BUT WE WERE TALKING ABOUT THE BACK PIMPLE, NOT THE CHEST PIMPLE.[/QUOTE]
You left out one point, I said that they would be at a maximum, but equal. Trivial cases aside, that is only true at terminal velocity. That's why there are two gauges. The skates only measure the reaction to the road, so that I could equate that to the friction to the belt, meaning I ignored the bodily wind drag in both cases.
So, once acceleration is over, there should be a stable reading of a maxima.
The parachute may be capable of more force according to its velocity wrt the wind, but that is also true of the belt. Two directly comparable tests will show a difference.

You are also getting that the person has mass, so works must be done to meet the KE. That is also wrong.

There is no real tailwind.
Because the wind is actually generated by dragging the object through the air (down the belt) the force against that same object can never be greater than the force dragging it. This is not true of real wind.
A balance is forced by that "still wind" condition, and driven to a minimum as that object goes towards winspeed.

 

[humber]

He avoided mentioning them because neither are true.

Both a gyro and a accelerometer only react to changes -- and changes aren't applicable to a steady state test.

Keep waiting for that change -- the very definition of 'steady state' means that the change you wait for isn't coming.

JB

The gyros and GPS are absolute wrt ground. That's all I need. You cannot force conditions until all information is excluded, because then it becomes effectively invisible. So, infinite and now invisible. Your treadmill is indeed special.
Also, your claim is denied because you cannot avoid my agreement as to what is not moving.

 

[mender]

There is no real tailwind.
Because the wind is actually generated by dragging the object through the air (down the belt) the force against that same object can never be greater than the force dragging it.

Right. As shown in part 2, force isn't an issue - lots available. DDWFTTW doesn't violate that.

This is not true of real wind.

Your next sentence needs explaining, humber. Are you saying that you can exceed the force available when you are dealing with the "real wind"? And how is it different from the "generated wind"?

 

[spacediver]

In wind, if you wear a pair of skates, and launch a parachute so that it carries you down wind. Eventually, you will reach terminal velocity. Strain gauges to the parachute and in the skates, will show forces to be opposite, but at a maximum.That is the real world case for down wind travel.

Humber, this is what you said, and you're completely wrong, unless I'm misunderstanding you.

The parachute will be under maximum tension at the beginning of the acceleration, because that is when the force of the wind is the greatest, since the relative velocities of the wind and parachute are most disparate at that point in time.

You seem to be confusing the terminal velocity in this example with free fall terminal velocity, which is a slightly different beast.

 

[John Freestone]

I would be more likley to ask you to figure it out for yourself with some helpfull guidance. You would start by diagraming all the forces involved. Gravity and the normal force from the table cancel and can be ignored for now. The force from traction, the linear inertial force the torque and the angular inertial force all have to balance so it's just a little bit of algebra to find the answer. [Hint: if you are not up to calculating the moment of inertia for simple geometries you could just look it up in the list of moments of inertia^WP ]

This isn't off-topic since it is preliminary to doing the calculations for the ddwfttw cart.

Thanks, Dan. I'm not sure I'm into the maths that much. I'm sure it's useful, but I seem to have described the process in all its detail other than putting numbers to the different forces. If I felt it was important for me to quantify them, I suppose I could overcome my slight discomfort with maths and get my head round it. I just wanted to offer a non-mathematical solution to humber's question for now. The subject is interesting. It has taken over enough of my life as it is without having to be able to do a full mathematical analysis of it.

 

[ThinAirDesigns]

The gyros and GPS are absolute wrt ground.

A gyro is not absolute relative to the ground and reacts only to change -- by definition, changes aren't coming in a steady state test. GYRO USELESS!!

GPS violates the "without external reference" requirement of the test. GPS USELESS!!

That's all I need.

What you need is *one* tool (yes, just one) that will allow you to determine *steady state* movement *without external reference*.

You continue to present tools and tests that violate the very definition of the stated problem.

Also, your claim is denied because you cannot avoid my agreement as to what is not moving.

A humberism, classic in it's convolution.

JB

 

[Marcus]

No he didn't. You have nothing to say.

Such a short memory. That was only a few days ago.

 

[humber]

A gyro is not absolute relative to the ground and reacts only to change -- by definition, changes aren't coming in a steady state test. GYRO USELESS!!

GPS violates the "without external reference" requirement of the test. GPS USELESS!!

No. You have a naive view. You take the idea that if information is excluded, so that you can discriminate less (a natural consequence of information itself), to mean that you can do so to useful effect.

I am afraid that gyros meet your steady state requirement. They are used as navigational instruments world wide. You can the entire world they are wrong about that. Unless you have also excluded time, I can therefore tell my velocity wrt the ground.

What you need is *one* tool (yes, just one) that will allow you to determine *steady state* movement *without external reference*.

I have that as you now know, but you cannot first put me in that steady state, without the accelerometer alerting me to that fact.

Once again, you cannot say your belt is moving, without first getting my agreement as to what is not moving.

You continue to present tools and test that violate the very definition of the test.
A humberism, classic in it's convolution.
JB

You are trying to redefine the claim after the fact. A classic retreat.

 

[mender]

Thought experiment:
If the power obtained from the rotation of the axle is used to power a mass chucker (100% efficient ion cannon, rail gun, etc.) instead of the propeller would the cart exceed the down wind speed?

Even assuming 100% efficiency, I suspect that the answer is no.

Davefoc, the propeller is a "mass chucker". It is flinging chunks of air backwards. By flinging the air back, it provides a propulsive force. The prop interacts with the air directly even though the prop is moving forward faster than the wind. It does that on a plane as well.

The amount of force available to power the "chucker" is quite a lot as shown in part 2. The propeller only has to fling the chunks of air back at a fraction of the speed that the wind is traveling at for the cart to harness that power. The propeller only needs to be reasonably efficient, certainly not 100%.

The cart can and does exceed windspeed. It also exceeds treadmill speed which for most people is just as "impossible", and is a lot easier to demonstrate.

 

[humber]

Humber, this is what you said, and you're completely wrong, unless I'm misunderstanding you.

The parachute will be under maximum tension at the beginning of the acceleration, because that is when the force of the wind is the greatest, since the relative velocities of the wind and parachute are most disparate at that point in time.

Then it is accelerating. That will happen until opposing forces equal that of the parachute. That's its maximum velocity. If there is no significant opposing force, then why does it not continue to accelerate?
The skater can't be pulled by the parachutes 'velocity' alone.

You seem to be confusing the terminal velocity in this example with free fall terminal velocity, which is a slightly different beast.

But you seem assume that the the skater will get to wind velocity at some minimum force.
The real skater will not do that. There will be a maximum velocity. Like a free falling object. The force of gravity is replaced by that of the parachute.

 

[Modified]

I have that as you now know, but you cannot first put me in that steady state, without the accelerometer alerting me to that fact.

You must initialize the accelerometer in the same way in both tests, at steady state on the surfaces.

Once again, you cannot say your belt is moving, without first getting my agreement as to what is not moving.

Ah-ha! You have accidentally said something that is true.

You are trying to redefine the claim after the fact. A classic retreat.

You do not understand the claim. Initializing some instrument off the belt and then carrying it onto the belt can introduce an external reference.

 

[mender]

The skates will be at maximum drag when the skater is at maximum speed, but the force provided by the parachute will be less than what it provides when accelerating the skater.

The question of whether the force provided by the parachute when the skater is at maximum speed in a particular wind is easily answered. Just provide the skater with a means of reeling in the parachute. If the skater's speed stays the same, then the parachute's force is at a maximum in that wind. If the skater's speed increases (which it will while slowing the parachute even more), then the force wasn't at a maximum but was merely balancing the drag of the skates.

If the skater can reel in the parachute fast enough, the skater can now move faster than the wind that is powering the parachute.

Another way for the skater to move faster than the wind is to have a pulley attached to the parachute with the skater holding both ends of the rope with a loop on one end of the rope. When the skater reaches maximum speed in the wind, they throw the loop over a stake pounded into the ice and hold on to the other end of the rope! Crack The Whip with a parachute!

 

[ThinAirDesigns]

I am afraid that gyros meet your steady state requirement.

Tell me what a gyro registers other than change? With the gyro in steady state, tell me which output you would read from the gyro to determine velocity and what it would read?

They are used as navigational instruments world wide.

Yes, to sense and to output *changes*. Not applicable in a steady state test.

You can the entire world they are wrong about that.

You can tell the entire world what you wish -- the gyro agrees with me and that is all that matters.

Unless you have also excluded time, I can therefore tell my velocity wrt the ground.

Tell me which output you would read from your timepiece to determine velocity and what it would read?

I have that as you now know, but you cannot first put me in that steady state, without the accelerometer alerting me to that fact.

You're still sensing change -- not relevant to a steady state test.

Once again, you cannot say your belt is moving, without first getting my agreement as to what is not moving.

I'm not saying my belt is moving -- I'm asking you to tell me if it is. You're saying that you can tell. You're failing however.

You are trying to redefine the claim after the fact.

Now you're just a simple liar -- post #2217 written ~10 days ago: (excerpts)

Me:
>There is absolutely no experiment which can be
>performed without external reference

>the treadmill is turned on steady state.

Both "external reference" and "steady state" are covered clearly.

>A classic retreat.

A classic humberism -- lie and hope to get away with it.

JB

 

[Christian Klippel]

A classic humberism -- lie and hope to get away with it.

Hello JB,

yea, he's pretty good at this. Also, twisting what was said seems to be a hobby of him. And let's not forget his claims like that you can use any measurement system to determine the actual velocity. I'd love to see him demonstrating that by simply using, lets say, a beaker. Or just a DMM. Or a clock. Or a scope.

He insisted that the wheels are slipping to increase the cart's performance, but when reminded about that silliness he says "i put you on fastscroll". He is even unable to eat his own words. What a poor mind he must have.

After all, the only thing he really wants is to make the cart fail, because in his twisted mind it can not work. So, no matter what you say or propose, it will always be wrong. Like the test you did. First he wanted you to do the test and when you did, but the outcome was not what he wanted, he accuses you of experimental fitting. Of course he completely neglects the fact that it was him who proposed that test and how it should be done.

He is unable to recognize that all he does is simply projecting. It is he who wants the cart to show a certain behavior which it would not show under normal circumstances. So he comes up with a lot of stupid things, in an attempt to make it show what he wants. Same with the gyro and stuff. While you clearly said "steady state" and "no external reference", he still sticks to using instrumentation and references. No matter what one would say, he is just inept to stick to what is said/proposed. Just so to make stuff fit the way he wants.

In short, he is absolutely unable to recognize his errors, let alone to admit them. It's like a child who is caught with the hands in the chocolate jar, having chocolate smear all over the hands, but insists that he didn't steal the chocolate and starts to yell and moan when he is told otherwise.

Greetings,

Chris

Edit: Also quite funny was his remark that if one would move with the treadmill's belt, that person would feel a headwind, no matter what.

If you are dragged by the belt, you get a headwind, not a tailwind. The "way" I am facing is not at all important.

Somehow it doesn't occur to him that by simply rotating that person by 180° this person would feel a tailwind then.

 

[ThinAirDesigns]

Same with the gyro and stuff. While you clearly said "steady state" and "no external reference", he still sticks to using instrumentation and references. No matter what one would say, he is just inept to stick to what is said/proposed. Just so to make stuff fit the way he wants.

He has the same problem on both sides of the coin -- to any precision he can't define a clear test and predict it's results. Neither can he follow another's clear test to any precision.

Things are very, very fuzzzzzy in Humberverse.

JB

 

[spork]

Taking one step back I have to ask humber this...

There are clearly a broad range of people on this forum with a broad range of backgrounds. Some clearly have advanced training in physics, some less so. Some clearly have good physical intuition, even if they don't have the training to go with it. But somehow you are unable to convince even one single person of one single fact. So you'd better face the fact that you are either completely wrong, or unbelievably bad at explaining your position. Because it's pretty hard to believe that something as simple as a 5.7 oz toy that consists of a gearbox a pair of wheels and a propeller couldn't possibly be understood by any of us.

So here's the new challenge.... forget about making your case to us, that's clearly never going to work. Forget about specifying a test, predicting an outcome, or doing a test of your own; that's clearly never going to happen either. The challenge is to find any one person, anywhere, that agrees with you. We'd like to hear from them.

 

[Subduction Zone]

spork if you remember one of humber's requests was for you to put more weight on your little cart. Since you did and it continued to work you obviously did not put enough weight on it. Now if you put a two ton weight on the cart I can guarantee you that it will perform up to humber's standards.