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Down wind faster than the wind

JB:
The offer was made to accept a model using Matlab, something that was well within the claimant's qualifications. They could be seen by all.
I see no reason to pay for an explanation that is not necessary, nor to keep it to myself.
Also, the offer required only the supply of what was many times promised, but not delivered, and restricted to the cart on belt problem.

I do not need to meet your demands. If you do not want to promote and support your ideas, then nobody is forcing you to do so. Placing claims on You Tube that you have something that defies conventional explanation, and then insulting those who would question you, is your choice.

If I take my car to be repaired, and it is placed upon a dynamometer, and the speedometer indicates 60mph, that does not mean that the car is going at that speed, nor that any of the aerodynamic properties of the car are being tested. For how long should I entertain such a notion?

I can add, that many cars have fans attached to the motors, this does not seem to give them any special properties. Simply setting up an artificial arrangement of these two ideas, does not make for anything that needs more than cursory examination. It has been heard, and its operation determined. Patents clerks see ideas like this by the bucket load. If that is not good enough for you, then return with something more substantive, or better supported.
 
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That's a neat toy. Thanks for all the good explanations as to why it works. I was stumped at first until I realised that the wheels were making the propeller turn against the wind.

This reminds me of Martin Gardner's spool that moves backwards. When you pull the string, the spool moves in the direction of the pull, moving faster than the hand that's doing the pulling.
 
I may be a layman, but it has been stated that this is a basic principle of physics, therefore I should be able to understand it. I do understand intertial frames of reference, at least enough to understand why when I'm sitting in a parked car and a car next to me drives away it looks like my car is moving backwards. Condescengly offering me lessons on it isn't going to win you points, and I'm not about to accept physics lessons from someone who I think is trying to trick me anyway.
I don't dispute what happens with the treadmill. It works exactly as I'd expect, in fact. The belt provides energy, indirectly, to the prop, creating thrust. The thrust is sufficient to overcome the drag, which is the traction of the wheel on the belt, and thus the cart advances. And it works because there is still enough traction for the belt to turn the wheel.
What I dispute is your assertion that the treadmill is equivalent to the open road and tailwind. And the reason I dispute that is because the wind can only push against objects moving slower than it. Just like when you're in a car moving 20 mph in a 20 mph tailwind and you stick your hand out the window, your hand experiences 0 mph of wind. I ask again, what force is moving the cart faster than the wind speed? I don't believe at this point I'm going to get a satisfactory and non-condescending answer.
As for the iceboat you keep talking about, I'm only familiar with iceboats that have powerful motors and wide flat keels. They are used for breaking the ice.
 
I'm convinced that the device can work.

What intrigues me is the problem of explaining it intuitively. Trying to craft intuitive explanations for complex or counterintuitive phenomena is something of a hobby of mine.

I'd like to try a different approach here, and I hope ThinAirDesigns spork, et. al. don't mind.

Imagine an inclined track, with a motorized chain running along it, like an old-fashioned roller coaster starting hill. The chain moves uphill, and let's also arbitrarily say that uphill is left to right (the top of the hill is toward the right).

The chain moves at some constant speed relative to the track. The chain is designed so that it can mesh with a sprocket wheel mounted in a vehicle that can travel along the track.

(We will assume that the return side of the chain, traveling in the opposite direction, is inaccessible below the track and will be completely disregarded. The only objects that our vehicle can come in contact with are the track and the forward-moving portion of the chain.)

The track has rough fixed high-friction surfaces (or, if you prefer, fixed racks in the rack-and-pinion sense) along its edges.

I will regard the following as obvious:

1. If the sprocket in the vehicle, that meshes with the chain, is fixed so that it cannot rotate, then the vehicle will travel along the track at the same speed as the chain. (Provided, which will go without saying henceforth, that the motor driving the chain can provide sufficient force.)

2. If the sprocket can rotate freely, without friction, then the vehicle will not travel forward along the track, except by its own momenum. From a standing start it would not move (if it's already at the bottom of the incline) or coast backward.

3. If the sprocket can rotate but its rotation is limited by a clutch, then the vehicle will either slip backward, remain stationary, or move forward along the track at less than or equal to the speed of the chain. It will only move at the speed of the chain if the clutch is sufficiently engaged to prevent the sprocket from rotating at all, which reduces to case 1.

4. If the vehicle has a motor in it that can drive the sprocket gear forward (clockwise, if the bottom of the sprocket is in contact with the chain and the forward direction of the track is left to right), then the vehicle can travel along the track faster than the chain.

The question for interested parties is, without modifying the track or chain, and without using a motor in the vehicle or making use of any stored energy (including stored kinetic energy) in any way, can a mechanism be installed in the vehicle that allows the vehicle to move along the track faster than the speed of the chain? What kind of mechanism might that be?

I believe, based on past experience, that for some the answer will be obvious but it might be elusive for others. Let's see what answers people have before proceeding further.

Respectfully,
Myriad

ETA: Dang, Michael C got there first, two posts ago. Please try to answer the question before clicking his link!
 
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JWideman said:
I may be a layman, but it has been stated that this is a basic principle of physics, therefore I should be able to understand it. I do understand intertial frames of reference, at least enough to understand why when I'm sitting in a parked car and a car next to me drives away it looks like my car is moving backwards. Condescengly offering me lessons on it isn't going to win you points, and I'm not about to accept physics lessons from someone who I think is trying to trick me anyway.
I don't dispute what happens with the treadmill. It works exactly as I'd expect, in fact. The belt provides energy, indirectly, to the prop, creating thrust. The thrust is sufficient to overcome the drag, which is the traction of the wheel on the belt, and thus the cart advances. And it works because there is still enough traction for the belt to turn the wheel.
What I dispute is your assertion that the treadmill is equivalent to the open road and tailwind. And the reason I dispute that is because the wind can only push against objects moving slower than it. Just like when you're in a car moving 20 mph in a 20 mph tailwind and you stick your hand out the window, your hand experiences 0 mph of wind. I ask again, what force is moving the cart faster than the wind speed? I don't believe at this point I'm going to get a satisfactory and non-condescending answer.
As for the iceboat you keep talking about, I'm only familiar with iceboats that have powerful motors and wide flat keels. They are used for breaking the ice.
Click to expand...

Agreed. I simply got tired of having to accept preposterous notions like the wheels are the ground, for the sole purposes of being able to call it a different
frame of reference. It is not necessary to go beyond what has been determined; that it is working against its own drag.
The simple answer is not enough, when you aver that it is, then out come the canned references and of course, "you know nothing about physics".
Boring.
ETA: As I think you mentioned, I also toyed with things like this when I was a boy. Where do they get the idea that science should dance to their tune?
 
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my_wan said:
What you have done is changed the gear ratio to make yourself right again.
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I did not change the gear ratio. In the first scenario, craft moving at 4 mph wrt ground results in the propeller moving air at 2 mph (wrt craft). This same, unmodified craft, when moving at 1 mph wrt ground, will result in the propeller moving air at 0.5 mph (wrt craft). This is because the gear ratio, and everything else, was not changed. The ratio of craft speed wrt ground and prop air speed wrt craft is constant.

my_wan said:
I admitted and fully explained that you can change sporks specifications to do this for real. I also explained in detail why sporks design as he specified is not geared this way, i.e., 1 to 1 rpm ratio and wheel diameter less that prop diameter. Read the rest of my response for more detail.
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I did read it, but I'm afraid it's not true. This statement

my_wan said:
The prop has a much larger radius than the wheels. This means the tips of the prop has to have a higher angular velocity than the edges of the wheels on the road, even at the same rpm. Any part of the prop with a greater radius of the wheels must eject air faster than the wheels are moving the craft.
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does not universally hold, because it doesn't consider the propeller pitch at all. If propeller pitch is sufficiently small, this will not be true.

But that's just a reason why it doesn't have to be true; it's not a reason why it's not true for Spork's device.

The reason why it's not true for Spork's device, as he specified and built it, is that it is not true, as a matter of fact. Let me demonstrate this.

HEY, SPORK!

Your device, as you specified and built it - does it eject air (wrt craft) faster than the wheels are moving the craft, or slower? Which is it?
 
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my_wan said:
It's not the "propeller pushing the air backwards which supplies the forward momentum". At below wind speed it is the wind blowing the craft itself downwind with force.
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But once the craft is moving at (or faster than) wind-speed, it is the propeller pushing the air backwards which pushes the craft forwards. Unless the craft is being pushed forwards by an external force, the only way it can accelerate is by pushing something backwards (in this case, the air). Equal and opposite reactions, etc.

I'm thinking of the propeller simply as a kinetic energy transfer device, providing forward momentum to the craft by transferring backwards momentum to the air, using kinetic energy extracted from the momentum of the ground (relative to the craft) via the wheels.

Am I misunderstanding this?

I'm also thinking of this device as exactly analogous to a wind-powered device pushing against the ground to move against the wind. (Only it's a ground powered device pushing against the wind to move against the ground.)

Are there any reasons why this wouldn't be exactly analogous?

In both cases, the devices would have to be geared-down in order to accelerate in the opposite direction against the source of it's motive force.

Thabiguy said:
Yes - if the transmission is right. If the propeller was just blowing air backwards at the same speed that the treadmill moves, then the thrust generated by the propeller would be cancelled by equal but opposite force exerted by the treadmill on the cart as it drives the propeller, and nothing would happen.

In order for the device to accelerate, the propeller must be geared to move the air slower (wrt device) than the ground moves (wrt device). Speed will be slower, but exerted force will be greater. This is what will generate the net forward force to accelerate the vehicle.
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As it must be geared-down this means that a wind-powered device can't travel more than wind-speed against the direction the wind is blowing, and a ground-powered device can't move more that ground-speed against the direction the ground is moving (which means it can't travel more than twice wind-speed in the direction of the wind, once you change frames of reference).

(Of course, if you can change gear-ratios once you've sped up, this no longer applies. :) )

That's how I think it should be working.
Am I understanding it right? :scared:
 
Thabiguy said:
HEY, SPORK!

Your device, as you specified and built it - does it eject air (wrt craft) faster than the wheels are moving the craft, or slower? Which is it?
Click to expand...


Slower. For this thing to work the advance ratio (prop vs. wheels) must be below 1.0
 
This is the basis of their claim that the treadmill represents a real wind test.
It can be found at #306

A:
Windspeed 10mph
Vehicle speed 10mph
Difference 0mph

B:
Windspeed 10mph
Vehicle speed 0 mph
Difference 10mph (sign ignored)

Their conclusion: When the difference is 0, the car is at windspeed.

The treadmill is said to have a property that allows case A to be assumed.

They forgot C:
Windspeed 0mph
Vehicle speed 0mph
Difference 0mph

So which is it?
in case A: Kinetic energy = 1/2mV^2
in case C: Kinetic energy = 0

Despite visible evidence for C, marginal speed, no kinetic energy, no wind.
They insist that it must be A: the vehicle is at windspeed and not essentially stopped.

LOL, genius
 
JWideman said:
I do understand intertial frames of reference, at least enough to understand why when I'm sitting in a parked car and a car next to me drives away it looks like my car is moving backwards.
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When it comes to understanding inertial frames of reference, we'll call the level you have described above, "Level X"

What I dispute is your assertion that the treadmill is equivalent to the open road and tailwind.
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No offense, but what's clear is that a "Level X" understanding of inertial frames of reference apparently isn't enough because the treadmill IS the physics equivalent of the open road.

Condescengly offering me lessons on it isn't going to win you points, and I'm not about to accept physics lessons from someone who I think is trying to trick me anyway.
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I now understand why you will not engage on the subject. Fair enough. For the record, I don't find anything "condescending" in my attempts to engage you. I believe you simply consider the statement "you don't understand the basics of inertial frames of reference" to be condescending -- but I can't change the facts to make them seem more palatable to you. Randi wouldn't approve.

IF you wish to understand the DDWFTTW concept of this device, you should find someone qualified who you *don't* think is trying to trick you and accept physics lessons from them. Your understanding of basic inertial frames of reference is lacking and could be proven to be so quite easily if you would engage.

JB
 
humber said:
This is the basis of their claim that the treadmill represents a real wind test.
It can be found at #306

A:
Windspeed 10mph
Vehicle speed 10mph
Difference 0mph

B:
Windspeed 10mph
Vehicle speed 0 mph
Difference 10mph (sign ignored)

Their conclusion: When the difference is 0, the car is at windspeed.

The treadmill is said to have a property that allows case A to be assumed.

They forgot C:
Windspeed 0mph
Vehicle speed 0mph
Difference 0mph

So which is it?
in case A: Kinetic energy = 1/2mV^2
in case C: Kinetic energy = 0

Despite visible evidence for C, marginal speed, no kinetic energy, no wind.
They insist that it must be A: the vehicle is at windspeed and not essentially stopped.

LOL, genius
Click to expand...

Kinetic energy is relative to some reference frame. The vehicle maintaining speed on the treadmill has kinetic energy in the reference frame of the tread surface, but not in the frame of the room (apart from the inertia of the prop).
 
Modified said:
Kinetic energy is relative to some reference frame.
Click to expand...


THANK YOU for that. I don't know why, but this is a point that's completely lost on most people. They think that a bullet shot through the air HAS some specific kinetic energy. They don't realize that its kinetic energy can be anywhere between 0 and astronomical depending on your reference frame.

Kinetic energy is NOT an intrinsic property.
 
Brian-M said:
As it must be geared-down this means that a wind-powered device can't travel more than wind-speed against the direction the wind is blowing, and a ground-powered device can't move more that ground-speed against the direction the ground is moving (which means it can't travel more than twice wind-speed in the direction of the wind, once you change frames of reference).
Click to expand...

Well, not necessarily. The gearing works both ways. I'll give you a specific example: if the propeller is geared to move the air backwards (wrt craft) at 2/3 of the wheel speed, the propeller-moved air is moving forward (wrt ground) at 1/3 of the craft speed. The wind will accelerate the craft until the propeller-moved air is moving forward (wrt ground) at the same speed as the wind. But because propeller-moved air is moving at 1/3 craft speed, this means that by this time the craft is moving at 3 times the wind speed.

Brian-M said:
Am I understanding it right? :scared:
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You care whether you understand, and that means you're on the best way to understanding! :)
 
humber said:
LOL, genius
Click to expand...

JB probably wouldn't want me divulging this, but he is in fact - literally a genius. As such your sarcastic rant may not have the effect desired.

What's more interesting is a story JB told me recently that's too long to recount here, but the spoiler is this... there is no way for stupid people to tell they're stupid. Of course this is a pretty pedestrian way of summarizing the results of a carefully controlled study.
 
Thabiguy said:
You care whether you understand, and that means you're on the best way to understanding! :)
Click to expand...

I second that. And my hat's off to you for opening yourself up to the possibility of something that just doesn't seem right intuitively.
 
While I can understand how the device works in still air on a treadmill, I'm still trying to see how it works on the ground with a tailwind. My thinking so far is along the lines of:

The wind pushes on the air from the prop, applying a torque to the prop, which through the transmission applies a torque to the wheels to drive the cart along the ground in the direction of the wind.

Is this correct?
 
JWideman said:
What I dispute is your assertion that the treadmill is equivalent to the open road and tailwind. And the reason I dispute that is because the wind can only push against objects moving slower than it. Just like when you're in a car moving 20 mph in a 20 mph tailwind and you stick your hand out the window, your hand experiences 0 mph of wind.
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That's more like it - a polite and reasonable question.

Here's the deal. All of the equations of physics depend only on differences in velocities, not on velocity itself. There is no absolute rest frame, no special velocity at which the laws of physics are different than at other ones. This is pretty obvious if you remember that the earth is hurtling through space at a gigantic velocity relative to every other thing in the universe.

A consequence of this fact is that one can add or subtract any velocity from all the velocities in a given problem without affecting the equations (since that addition or subtraction cancels out of all velocity differences). That's called transforming to a different reference frame. OK?

So - imagine a cart in a steady wind on flat ground. The cart is rolling at exactly the speed of the wind (say 20mph), and in the same direction. Someone riding the car feels no breeze at all, just as you said. But the ground is moving past them at 20 mph, and the wheels of the car are spinning at the appropriate rate (which depends on their radius).

Now, transform from the reference frame in which the ground is at rest and the cart is moving (the "ground" frame) to the one where the cart is at rest and the ground is moving (the "wind" frame). Wind speed in the first frame is 20 mph, in the new frame it's 20mph-20mph = 0 (that's why I called it the wind frame). But ground speed is 0-20mph = -20 mph (the minus means it's going the opposite way the wind was).

So in the new frame the cart and wind are at rest, but the ground is moving. That's precisely the cart at fixed position (relative to the treadmill, not the belt) on the treadmill. Its wheels are spinning, but it's in still air (apart from the breeze that's created when the propeller is attached to the wheels).

I ask again, what force is moving the cart faster than the wind speed?
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The propeller, which is driven by the moving belt.
 
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Don't forget to include the greast big hand that will magically take the cart from 0mph to 10mph, instantaneously and without any apparent energy exchange.

All things are relative. How literal can you be?
 
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