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Down wind faster than the wind

humber said:
The treadmill is not equivalent to a windtunnel.
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You just keep repeating that. Of course they are equivalent. Both create a constant velocity difference between air and surface. One allows moving at ground speed without ever leaving the device, while the other allows moving at air speed without ever leaving the device.

Show me a text that supports that idea.
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(Pulls intro physics book off shelf) ... Frank J. Blatt, Principles of Physics, Second Editon, Page 39, "the laws of physics are unaltered as we change from one reference frame to another, provided that the two are inertial frames. Physicists say that the laws of nature are invariant with respect to a change of inertial reference frames. This is not a particularly difficult or strange concept."
 
Spork, A couple night ago, I thought for sure that your videos must be fakes and looked fro every conceivable way that the trick could have been pulled off. Invisible strings are one obvious method though you try to prove there can be no strings just like a good magician.

The next thought was an external wind source. I even went to the trouble of identifying the treadmill you used and was disappointed that the model 400 X specs don't list a cooling fan.

Then there is the placement of the treadmill next to the door with a curtain blocking the view of the outside. You could have removed the bottom of the treadmill base under the belt and have an accomplice outside manipulating a stick with magnets that attract the wheels of the cart.

As I went to bed thinking what a cleaver spoof this could be, the thought of the mechanics of a yo-yo kept interrupting. But could a string be replaced with the wind?
 
Dan O. said:
Spork, A couple night ago, I thought for sure that your videos must be fakes and looked fro every conceivable way that the trick could have been pulled off...
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As you should. But I offer several solutions to that.

1) Tell me what do tape and I will do so if I can. We've posted several videos already to address individual concerns that have been brought up.
2) Stop by for a demo. You can take it apart and put it back together. You can inspect every conceivable part of it and the surroundings. Don't like my treadmill, we'll go to a gym.
3) Build your own. I'll give you a parts list.

As I went to bed thinking what a cleaver spoof this could be, the thought of the mechanics of a yo-yo kept interrupting. But could a string be replaced with the wind?
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Now you're onto something. But don't take my word. Come see it or build one yourself.
 
Michael C said:
No, I'm not avoiding the question. Once again:

Kinetic Energy is a relative property

It's not a question of the kinetic energy being "there" or "real". The kinetic energy of any object will have a different value, depending on which inertial frame you use to measure it. It's nonsense to say that the kinetic energy of a car is equal to a certain value without defining the frame of reference. For most situations, it is tacitly assumed that the frame of reference is that of the surface of the earth. When we get to comparing cars on treadmills with cars running on roads, however, it becomes important, to avoid confusion, to define the frame of reference. A car running at 60 km/h along a flat road has a certain kinetic energy relative to the frame of reference containing the road. It has zero kinetic energy relative to a frame of reference moving at the same speed as itself.

As for making a car run a treadmill by holding it in place and turning the wheels against the surface of the treadmill, it's not the "kinetic energy" of the car that's making the treadmill turn. The car is simply acting as a motor for the treadmill, imparting energy from its turning wheels. When the treadmill is being turned by its own motor, is it the kinetic energy of the motor that makes it turn?
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Yes, sorry. You don't generally do that.


A car that is stationary, has kinetic energy due to the fact that it is rotating with the surface of the Earth. A second car has this, plus that due to its motion relative to that same surface. That is what you are saying?

OK, but you can simply perform a translation or transform from the ground.
But using only velocity or a few selected parameters, leads to errors, and when not, it is just a mathematical exercise, done for convenience, perhaps.

Two identical cars;
Belt drives car to 60mph. Belt and moving masses are negligible. Connect generator to the car's wheel as the belt is turned off. The generator's output is stored in a battery. Do the same with a real car, but turning off the engine.

One will store much more than the other. In fact, the charge from the treadmill car, will be essentially that of a static car.

The car on treadmill has yet another feature of a static car, and one fewer than the real car.
Why?
 
humber said:
Two identical cars;
Belt drives car to 60mph. Belt and moving masses are negligible. Connect generator to the car's wheel as the belt is turned off. The generator's output is stored in a battery. Do the same with a real car, but turning off the engine.

One will store much more than the other. In fact, the charge from the treadmill car, will be essentially that of a static car.
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You have not done identical things in both cases. If you're going to stop the belt, then you must also accelerate the ground beneath the car on the road in an identical fashion.

To make them the same, in both cases you should turn off the car engine. The belt should continue running, and must be long enough so that the car can slow down until its speed matches the belt speed without running off the end of the belt. The energy stored will be the same for both cars, assuming the treadmill motor can maintain constant belt speed under such conditions.
 
Modified said:
You just keep repeating that. Of course they are equivalent. Both create a constant velocity difference between air and surface. One allows moving at ground speed without ever leaving the device, while the other allows moving at air speed without ever leaving the device.

(Pulls intro physics book off shelf) ... Frank J. Blatt, Principles of Physics, Second Editon, Page 39, "the laws of physics are unaltered as we change from one reference frame to another, provided that the two are inertial frames. Physicists say that the laws of nature are invariant with respect to a change of inertial reference frames. This is not a particularly difficult or strange concept."
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Yes, that is taken as read. As the last line suggests, it's not rocket science.

However, it needs to be handled with care or you end up equating treadmills and windtunnels, and elephants with mice.

See: http://en.wikipedia.org/wiki/Mathematical_maturity
 
Modified said:
You have not done identical things in both cases. If you're going to stop the belt, then you must also accelerate the ground beneath the car on the road in an identical fashion.

To make them the same, in both cases you should turn off the car engine. The belt should continue running, and must be long enough so that the car can slow down until its speed matches the belt speed without running off the end of the belt. The energy stored will be the same for both cars, assuming the treadmill motor can maintain constant belt speed under such conditions.
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How will you know when it's long enough?
Any way, that's a property of the tread mill, and that is fixed to the ground. The real car has stored energy, because it has been accelerated, but the other not.
OK leave the treadmill running, but lift the car so there is no contact.
 
humber said:
How will you know when it's long enough?
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If it can slow to a stop with respect to the treadmill belt before it runs off the end. The same applies to the road.

Any way, that's a property of the tread mill, and that is fixed to the ground. The real car has stored energy, because it has been accelerated, but the other not.
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Stored kinetic energy is relative.

OK leave the treadmill running, but lift the car so there is no contact.
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Then you must do the equivalent to the car on the road - lift it up and continue carrying it forward at wind speed.
 
Michael C said:
This vehicle isn't just moving because of its kinetic energy. It doesn't need a push to get started. It is indeed using the energy from the wind. By "wind" we have to be careful what we mean: we are not talking about the speed of the air relative to the vehicle, we are talking about the speed of the air relative to the ground.



No, because the wheels are turning against the ground, causing the propeller to turn against the air.



No, see above.



Not for the blades of the turning propeller. It's true that the rest of the vehicle loses the advantage of the tailwind, but as you can see from the video, only a very small surface is being pushed by the tailwind. The propeller is still churning through the air, producing a forward thrust. The vehicle will reach a point where the speed of the propeller is exactly adapted to the speed of the vehicle through the air: no more drag is produced and the vehicle stays at a steady speed.
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The wheels are turning against the ground only because the wind is moving the vehicle relative to the ground. If it wasn’t for the wind the vehicle wouldn’t move relative to the ground at all. When the vehicle reaches the speed of the wind there is no wind speed left to move it relative to the ground any faster. Yet you say that it can accelerate from this speed to go faster than the wind. Where does the energy to do this come from? It can’t come from the wind or the kinetic energy of the vehicle.
 
ThinAirDesigns said:
It surprises me that with a group this bright, the troll is still being fed.
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You could be right. I'm still operating under the impression that humber has trouble visualizing a change of reference frames and can't get over the idea that the reference frame of the ground is special. His misunderstandings seem fairly consistent for an intentional troll.
 
spork said:
So if someone holds me off the ground and then carefully lets me go, and I continue to levitate indefinitely, you won't be impressed. You really are a tough audience.

Wanna bet?

Wanna bet?

Wanna bet?

Didn't think so. You just want to B.S.
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I assure you I would be extremely impressed if actual levitation could be credibly demonstrated (but I won‘t hold my breath).

Here is a test suggestion . . .

Let your vehicle run freely down a long incline and time how long it takes to travel from the top to the bottom. Then disconnect the drive from the wheels to the propeller (but leave them in place) and let it run down the incline again. If your claim is correct the connected propeller vehicle should complete the journey faster than the disconnected. Does it?
 
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ynot said:
When the vehicle reaches the speed of the wind there is no wind speed left to move it relative to the ground any faster. Yet you say that it can accelerate from this speed to go faster than the wind. Where does the energy to do this come from? It can’t come from the wind...
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Sure it can, as long as parts of the vehicle are not moving downwind at wind speed, which the blades of the prop are not.
 
ynot said:
I assure you I would be extremely impressed if actual levitation could be credibly demonstrated (but I won‘t hold my breath).

Here is a test suggestion . . .

Let your vehicle run freely down a long incline and time how long it takes to travel from the top to the bottom. Then disconnect the drive from the wheels to the propeller (but leave them in place) and let it run down the incline again. If your claim is correct the connected propeller vehicle should complete the journey faster than the disconnected. Does it?
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Not to be rude, but you probably should read the whole thread. That question has been asked and answered.
 
ynot said:
When the vehicle reaches the speed of the wind there is no wind speed left to move it relative to the ground any faster. Yet you say that it can accelerate from this speed to go faster than the wind.
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Your above comment really is the key to the entire brainteaser. I know it's exactly where I was stuck until I realized my error.

We all initially think about the wind relative only to the chassis of the cart -- yes, when the cart is moving the speed of the wind there is no wind over the chassis.

The key to understanding this is to notice that in spite of there being no wind over the frame of the cart, there still remains wind relative to the ground, and there still remains wind relative to the sails of the cart.

This is no different than an ice-boat or sailboat reaching at 45degrees with a VMG of 1.0 -- the boat is going VMG downwind *exactly* the speed of the wind and yet the sail still sees wind and the boat accelerates onto a VMG of greater than 1.0.


Where does the energy to do this come from? It can’t come from the wind or the kinetic energy of the vehicle.
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You are correct that it can't come from kinetic energy, but it IS coming from the wind -- the wind hasn't stopped blowing across the ground after all and neither has it stopped blowing across our 'sail'.

JB
 
Modified said:
If it can slow to a stop with respect to the treadmill belt before it runs off the end. The same applies to the road.

Stored kinetic energy is relative.

Then you must do the equivalent to the car on the road - lift it up and continue carrying it forward at wind speed.
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The belt has very low mass. The car is in the usual stationary position, and the belt is 10m long. I am unaware of the car's mass, or the the other car on the road. The energy is stored, so I can make comparisons at my leisure.

The generator is a big load. It brings the car to a stop within 5 meters.

One has charge, and the other not.

I think the difference is that one car has been accelerated, and the other not.
 
ynot said:
Here is a test suggestion . . .

Let your vehicle run freely down a long incline and time how long it takes to travel from the top to the bottom. Then disconnect the drive from the wheels to the propeller (but leave them in place) and let it run down the incline again. If your claim is correct the connected propeller vehicle should complete the journey faster than the disconnected. Does it?
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Your test demonstrates your fundamental lack of understanding of the device. You have asked for the device to be tested with it's power source (relative motion between wind and rolling surface) turned off.

Yes, you have replaced the 'wind' power source with a slope (gravity), but the device isn't designed to be gravity powered so what does it prove?. Try inverting the gasoline and diesel fuels in two perfectly functioning engines and see how they work.

Energy sources are not necessarily interchangable.

JB
 
Modified said:
Not to be rude, but you probably should read the whole thread. That question has been asked and answered.
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Couild you please provide the number of the post that "answers" it? - Thanks

No need I found it.
 
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