Merged DDWFTTW in a “Real” Wind

[BowlOfRed]

If you assume that the object is already at 1ms-1 wrt the train, then the 50ms-1 drops out. and both cases are 0W and 1W

Work = force*distance
= F*( u + 1/2at^2)
With respect to the floor of the train u = 0, and for constant motion a = 0.
so
Work = f*d = F*v*t
v =1ms-1

While correct (in the reference frame of the train), it doesn't seem to speak to the original question about the difference with how work is interpreted between different frames (#5535), nor to whatever is "not quite right" with my response to it (#5571).

 

[windgrins]

A straightforward question for BowlofRed.

While correct (in the reference frame of the train), it doesn't seem to speak to the original question about the difference with how work is interpreted between different frames (#5535), nor to whatever is "not quite right" with my response to it (#5571).

BowlofRed,

I don't know how much of this forum you've read but you seem like a reasonable guy. I'd like your opinion on the following:

For the purpose of producing a device that could go DDWFTTW using only the wind, it has been posited by some on this forum that a device that can achieve this in a 15km tailwind should be able to prove this in the following manner:

Either A. by going greater than 15km/h over the ground on level ground with a 15km/h steady direct tailwind. (Obvious demonstration of the fact.)

Or B. by being placed on a level treadmill facing up tread (ie opposite the direction of belt motion or towards the handlebars on a conventional exercise treadmill) with the treadmill running at a constant 15km/h. The device is to be placed on the treadmill and allowed to reach steady state by holding it in place. If, once released at 0 velocity with respect to the frame, the device is able to accelerate up the belt using no stored power of any sort. Is this equivalent and even actually is going dead down wind faster than the wind?

The fundamental question is: Is moving on the treadmill at 15km/h beltspeed in still air the same as moving over the ground at 15km/h with a 15km/h tailwind?

And would you please explain your answer with a few short remarks.

Thanks and Regards,

WindGrins

 

[humber]

While correct (in the reference frame of the train), it doesn't seem to speak to the original question about the difference with how work is interpreted between different frames (#5535), nor to whatever is "not quite right" with my response to it (#5571).

The use of 50W is not right. At some point the table must be accelerated to 51ms-1. That takes energy from the train.

When at constant velocity of 1ms-1, the force applied to the floor due to pushing, will be seen at the train's wheels, but no work is done because that is cancelled out by the opposing force from the table. The net work due to the motion of the train is zero, and instruments attached to the engine or the pusher will not show the presence of that 50W.

 

[humber]

BowlofRed,

I don't know how much of this forum you've read but you seem like a reasonable guy. I'd like your opinion on the following:

For the purpose of producing a device that could go DDWFTTW using only the wind, it has been posited by some on this forum that a device that can achieve this in a 15km tailwind should be able to prove this in the following manner:

Either A. by going greater than 15km/h over the ground on level ground with a 15km/h steady direct tailwind. (Obvious demonstration of the fact.)

Or B. by being placed on a level treadmill facing up tread (ie opposite the direction of belt motion or towards the handlebars on a conventional exercise treadmill) with the treadmill running at a constant 15km/h. The device is to be placed on the treadmill and allowed to reach steady state by holding it in place. If, once released at 0 velocity with respect to the frame, the device is able to accelerate up the belt using no stored power of any sort. Is this equivalent and even actually is going dead down wind faster than the wind?

The fundamental question is: Is moving on the treadmill at 15km/h beltspeed in still air the same as moving over the ground at 15km/h with a 15km/h tailwind?

And would you please explain your answer with a few short remarks.

Thanks and Regards,

WindGrins

The cart is at 0m/s wrt the ground. The cart stays in place, while the belt moves the other way. The cart does not travel at 15m/s wrt the belt, but the belt travels at -15m/s wrt the ground.

The analogy is with a tablecloth pulled from under the dishes. If the dishes do not move at all, the tablecloth does only the work of friction to the table.
The smaller friction between the dishes and the cloth, moves the dishes to some degree.
If the tablecloth is secured to a wall, and the table is moved, again the work done is against the friction of the tablecloth and table. Because the cloth is restrained by the static force to the wall, no work is done on the dishes.
The prop provides that static force. Energy to provide that force comes from the belt.

 

[windgrins]

Please don't help me, Humber!

The cart is at 0m/s wrt the ground. The cart stays in place, while the belt moves the other way. The cart does not travel at 15m/s wrt the belt, but the belt travels at -15m/s wrt the ground.

The analogy is with a tablecloth pulled from under the dishes. If the dishes do not move at all, the tablecloth does only the work of friction to the table.
The smaller friction between the dishes and the cloth, moves the dishes to some degree.
If the tablecloth is secured to a wall, and the table is moved, again the work done is against the friction of the tablecloth and table. Because the cloth is restrained by the static force to the wall, no work is done on the dishes.
The prop provides that static force. Energy to provide that force comes from the belt.

I'm not sure your helpful clarification is making this easier!

WindGrins

 

[jduffy77]

Is it Bowl of Red or Bowl-o-Fred?

 

[Jack by the hedge]

Is it Bowl of Red or Bowl-o-Fred?

'fred for short? Welcome, Bowlofred, to the thread that keeps going but never moves on.

 

[Christian Klippel]

So in your car the engine directly pushes the driver?

That's interesting, in my car, the engine turns the wheels, the wheels move the body of the car, and the seat pushes on the driver. Could you post some drawings of the humbercar? I'd love to see how it works.

It will very likely use a bunch of humbersprings for suspension. You know, the ones that only extend/expand half the amount [Edit: half the amount each] if you put two in series, than what would any single of them would do, under the same load!

And it would use a bouncing speedometer that is not connected to anything. Because simply by bouncing (jumping) it can tell what moves. And from there it can deduce how fast, of course!

Greetings,

Chris

 

[Christian Klippel]

The cart is at 0m/s wrt the ground. The cart stays in place, while the belt moves the other way. The cart does not travel at 15m/s wrt the belt, but the belt travels at -15m/s wrt the ground.

Wow. So the cart does not move and also move, at the same time!

Almost worthy to be added to my sig-line. But only almost.

 

[fttw]

Obviously it's still 1 watt. So why is the calculation of force x distance now wrong?

Forces are not invariant between moving frames; the frictional force is less in the frame in which the train is in motion.

That seems counterintuitive, but some thought experiments will demonstrate it is so.

 

[Llyricist]

For anyone who cares, that "tornado" wind graph is what happened every time the Chase Vehicle was sitting still. It happened because the wind direction was calculated by vector addition of the wind direction and speed relative to the Chase Vehicle and the GPS reported bearing and speed of the chase vehicle.

And while sitting still, the GPS reports basically random bearings and speeds (on the order of .05 MPH), so the speed isn't really effected, but the bearings are all over the place.

 

[BowlOfRed]

Is it Bowl of Red or Bowl-o-Fred?

The avatar image is a hint, but perhaps not recognizable by all. A "bowl of red" is an alternate term for chili con carne.

I seem to remember attempting to use CamelCase to make it more obvious, but apparently failed.

 

[humber]

For anyone who cares, that "tornado" wind graph is what happened every time the Chase Vehicle was sitting still. It happened because the wind direction was calculated by vector addition of the wind direction and speed relative to the Chase Vehicle and the GPS reported bearing and speed of the chase vehicle.

Several errors there. There is unprocessed vane data.

1) The sudden transitions are due to the vane passing through the deas zone of the potentiometer.

2) The other chart was in response the this question about the results under towing etc.

You refuse to talk about the data from the time during which the cart was turning back to the starting position etc.
I am fully aware of when the reading as are valid or not.

http://www.internationalskeptics.com/forums/attachment.php?attachmentid=22119&stc=1&d=1305114178


This one, happens just after the CV has stabilized, so again, no error.
Again strong dependence upon wind change over time, and deviation from ddw. There is not enough data where the wind is stable, to assemble 10% of a chart out of the entire data set.

And while sitting still, the GPS reports basically random bearings and speeds (on the order of .05 MPH), so the speed isn't really effected, but the bearings are all over the place.

GPS, is a positional system, so does not give random bearings: not to be confused with the cart's Doppler.

 

[rehn]

When I read this:
http://www.utexas.edu/news/2011/05/05/schizophrenia_discern/
it occurred to me that it might have some relevance for this thread.
I am still not fully convinced that all participants here are real persons.

 

[69dodge]

Forces are not invariant between moving frames; the frictional force is less in the frame in which the train is in motion.

That seems counterintuitive, but some thought experiments will demonstrate it is so.

This seems wrong to me. Can you elaborate? What thought experiments?

I figure, F = ma, and a doesn't change between reference frames moving at constant velocity relative to each other, so neither should F.

(I believe that, in the theory of relativity, forces are not invariant between frames, but I don't suppose you're referring to that here. Or are you?)

 

[humber]

You can try and wish away all that you like, but you won't find many that will agree that a cart in winds that change by up to 60 degrees and rapidly, is anything like ddw.

 

[humber]

This seems wrong to me. Can you elaborate? What thought experiments?

I figure, F = ma, and a doesn't change between reference frames moving at constant velocity relative to each other, so neither should F.

(I believe that, in the theory of relativity, forces are not invariant between frames, but I don't suppose you're referring to that here. Or are you?)

"Thought experiment", "invariant" and "counterintuitive", all within two sentences, say more than the sentences.

 

[BowlOfRed]

BowlofRed,

I don't know how much of this forum you've read but you seem like a reasonable guy. I'd like your opinion on the following:
[...]
The fundamental question is: Is moving on the treadmill at 15km/h beltspeed in still air the same as moving over the ground at 15km/h with a 15km/h tailwind?

I enjoy reading the thread, but I think I'll leave any of the big questions for others. I felt confident addressing the specific points raised in that one post.

Given that I don't have the skills (or desire) to do a full mathematical analysis, I doubt that anything I could say on the subject would be different than what is already said.

But yes, I agree that the treadmill works fine as an analog.

 

[Llyricist]

Several errors there. There is unprocessed vane data.


[qimg]http://www.internationalskeptics.com/forums/attachment.php?attachmentid=22131&stc=1&d=1305179033[/qimg]
1) The sudden transitions are due to the vane passing through the deas zone of the potentiometer.

This is irrelevant, at worst that would show up as an instantaneous spike, in the calculated results. But it doesn't because it is instantaneous.

2) The other chart was in response the this question about the results under towing etc.

Then it was a dumb response, that's what happened while the CV was sitting still.

GPS, is a positional system, so does not give random bearings: not to be confused with the cart's Doppler.

This is just, flat, wrong.

 

[BowlOfRed]

The use of 50W is not right. At some point the table must be accelerated to 51ms-1. That takes energy from the train.

In the question I responded to, neither the train nor the object undergo acceleration during the duration of the experiment.