Merged DDWFTTW in a “Real” Wind

[humber]

As I have been saying, what is so funny about HcrisPrangGlossYev is that it was, as you say, his correct force calculations which showed that the cart must work which led him to start making the energy calcs.

There was no such act, and you have now conflated four, or is it five, names into one imaginary poster? One wonders how many of you are at home.

 

[fttw]

In so far as I understand the "arguments about the arguments", they're not very enlightening.

However, Profpangloss said he has an analysis, in the earth frame, that shows the cart doesn't/can't work. I'd like to see that analysis, if possible.

 

[humber]

In so far as I understand the "arguments about the arguments", they're not very enlightening.

However, Profpangloss said he has an analysis, in the earth frame, that shows the cart doesn't/can't work. I'd like to see that analysis, if possible.

I am sure you will. How are you on electrical analogues? That one too breaks the camel's back.

 

[drewid]

Of course all you need to do is post your video of the propless cart on the treadmill...

 

[humber]

Of course all you need to do is post your video of the propless cart on the treadmill...

That's not going to be here.

 

[windgrins]

It's in an earlier post, I believe. #5180 page 130

In so far as I understand the "arguments about the arguments", they're not very enlightening.

However, Profpangloss said he has an analysis, in the earth frame, that shows the cart doesn't/can't work. I'd like to see that analysis, if possible.

See post #5181 where I think he first presented it.

WindGrins

 

[drewid]

That's not going to be here.

Naturally.

 

[69dodge]

The usual way to deal with this, is to use instantaneous quantities like power (instead of work done over a certain time period). This allows you to use instantaneous inertial rest frames of accelerated objects, where the conservation laws hold.

I'm not sure what you mean. But it sounds interesting. Can you give a simple example, maybe? Thanks.

 

[fttw]

See post #5181 where I think he first presented it.

OK - I looked at 5181 and it's full of lots of "magic" numbers and also lots of invective. If you have to use numbers to make a physical argument, then that's ok - but let's make them generic, i.e. "assume the cart to be of unit mass" etc.

The problem with the invective is that it's a strongly worded post in reply to someone else's argument, which makes it difficult to follow and either agree with or refute the physics involved.

Could Profpangloss please present his argument "in neat", so to speak?

 

[69dodge]

I'm happy to assume that the mass of the earth is infinite, and that you're free to use it as an infinite source or sink for momentum without violating any physical laws, and that, equivalently, it forms an inertial frame.

But he doesn't want to use it as an infinite sink for momentum.

He wants to consider the earth as simultaneously having infinite mass and having zero mass: infinite mass so that it's an inertial reference frame, and zero mass so that it doesn't apply any force to the cart (equivalently, doesn't change the cart's momentum at all).

http://www.internationalskeptics.com/forums/showpost.php?p=7176246&postcount=5631

 

[fttw]

But he doesn't want to use it as an infinite sink for momentum.

He wants to consider the earth as simultaneously having infinite mass and having zero mass: infinite mass so that it's an inertial reference frame, and zero mass so that it doesn't apply any force to the cart (equivalently, doesn't change the cart's momentum at all).

I've looked through lots of posts, but it's so easy to misunderstand what people are saying, especially when they're responding to someone else. That's why I'd really like to hear Profpangloss put it all down in one post, so there's no need to refer back and forth.

 

[profpangloss]

OK - I looked at 5181 and it's full of lots of "magic" numbers and also lots of invective. If you have to use numbers to make a physical argument, then that's ok - but let's make them generic, i.e. "assume the cart to be of unit mass" etc.

The problem with the invective is that it's a strongly worded post in reply to someone else's argument, which makes it difficult to follow and either agree with or refute the physics involved.

Could Profpangloss please present his argument "in neat", so to speak?

Yes,I can do so, but I admit to being somewhat of a stickler for accuracy and precision, so the work will be very detailed. I don't want to go through all of that just to have someone reject it based on non-acceptance of the surface of the earth as an *almost inertial reference frame! The conservation of mass and energy must hold true in any inertial reference frame, as they are derived from Newton's Laws which hold. (Actually, the conservation laws are more fundamental than Newton' Laws, but historically they were derived after Newton.)

So, to try and get some sanity back into this discussion, I will do the analysis and post it as an analysis done in an "almost inertial frame of reference' where conservation of energy and momentum are "almost conserved". As ridiculous as that may seem, I believe the conservation of energy fails in such a big way, that no amount of figures lieing, or liars figuring, will save the cart!

Ok, enough preamble, now I need to get down to brass tacks and do the analysis.

You may want to read the Appendix in the NALSA submission report (Appendix 1) to get an idea of what I will be discussing as I plan on using that as a basis for my analysis, which I haven't done yet!

So it will be based upon someone else' argument, but you can make it generic quite easily, if you want.

 

[69dodge]

You may want to read the Appendix in the NALSA submission report (Appendix 1) to get an idea of what I will be discussing as I plan on using that as a basis for my analysis, which I haven't done yet!

The submission report can be found at http://www.nalsa.org/DownWind.html.

 

[fttw]

Let's address the earth-as-inertial-frame issue then.

Inertial frames aren't physical objects, merely points of view without a physical reality.

By definition, an inertial frame doesn't ever accelerate, whereas all physical objects are free to accelerate if and when acted on by an overall force.

It's legitimate to say the rest-frame of a real object is inertial, but only for as long as that object doesn't accelerate.

There are two ways to ensure that an object doesn't accelerate - either no forces act upon it, or else, it must have infinite mass.

In the cart thought-experiment, it's clear that a force acts upon the earth, reacting against the cart, otherwise there'd be no need for the wheels or the drivetrain.

Given that, if you want the earth-stationary frame to be inertial you'll have to assume the earth has infinite mass, so that whatever the force reacted against the cart, the earth doesn't accelerate.

In light of the fact that the earth is orders of magnitude more massive than the cart, I'm happy to adopt the infinite-earth-mass approximation for any analysis of the cart scenario.

 

[ThinAirDesigns]

God I can't wait for the same chryevschoglosH argument mistakes.

JB

 

[69dodge]

In light of the fact that the earth is orders of magnitude more massive than the cart, I'm happy to adopt the infinite-earth-mass approximation for any analysis of the cart scenario.

Are you also happy to assume that the momentum of the cart-plus-air is conserved?

 

[jduffy77]

I've looked through lots of posts, but it's so easy to misunderstand what people are saying, especially when they're responding to someone else. That's why I'd really like to hear Profpangloss put it all down in one post, so there's no need to refer back and forth.

Here is one from TR where he proves the cart must work with his force balance. His energy balance also shows the cart works as long as you correct his same old mistake. Uncool and Lyricist both corrected it for him already.

The parameters are: windspeed is 7 M/s, cart velocity is 9 m/s DDW, both measured wrt the ground which is not moving. Cart weighs 270 Kg and has a 5 m diameter propeller.

Let the wheels generate 1000 Watts as the cart moves over the ground at 9 m/s and the wheel drag is 111.1 N.

Note: All calculations are in the frame of reference where the ground is stationary and has NO energy. The cart, moving at 9 m/s and with a mass of 270 Kg has 10,935 Joules of Kinetic Energy. The 1000 J/s developed at the wheels comes entirely from this KE of the cart being transformed into 1000 J/s of energy at the wheels and then this energy is used to do Work at the propeller to exert a thrust force on the air, accelerating it.

Let the overall efficiency of the cart be 87.5% so that there is 875 J/s of Work being done at the propeller on the air. (In reality such a high overall efficiency is impossible as the propeller taken by itself will not have this high an efficiency, but I am using a best case analysis here)

Thrust = mass x acceleration = л/4•D^2•[v+∆v/2] • ρ•∆v where л/4•D^2•[v+∆v/2] • ρ is the mass of the air moving through the propeller and ∆v is the acceleration of the air by the propeller. With the 5 meter prop, л/4•D^2• ρ works out to 24. V is the velocity of the relative headwind and that we know to be 2 m/s in this case. We don’t yet know what the value of ∆v is and we don’t yet know the value of thrust.

However we do know the power absorbed by the propeller is 875 Watts (875 J/s) and there is another equation that says *Engine power = Thrust•[v+∆v/2]. So we can equate these two relationships to solve for ∆v and then solve for thrust:
л/4•D^2•[v+∆v/2] • ρ•∆v = *Engine power / •[v+∆v/2]

Let ∆v be replaced by x
48x + 12 x^2 = 875 / (2 +x/2)
12x^3 + 96X^2 + 192 x =1750, x ~ 2.99

So ∆v = 2.99 and plugging that into either or both of the above equations gives a value for Thrust = 250 N.

Wheel Drag is 111 N and we can calculate Rolling Resistance from mgCrr using Crr of 0.02 and RR = 53 N. There is also air drag due to the 2 m/s headwind but I am not going to bother calculating it and assume a reasonably low value of 10 N for a Total drag force of 174 N.

At this point the less informed among the cart crowd will say I have just shown the cart works, because the thrust is 250 N and the drag is 174 N, right? No, forces alone are not the whole story as we need to consider energy and power. The thrust force is what would be there IF and only IF, there is sufficient energy in the system to develop and sustain that thrust. Now we will see if that is the case or not:

We know the prop will accelerate the air mass passing through it by ∆v and that is 2.99 m/s (effectively slowing the 7 m/s wind down by that amount)

We can calculate the air mass from the thrust equation: air mass = л/4•D^2•[v+∆v/2] • ρ and we already have all the values to fill in: = 24 (2 +1.5) = 84 Kg.
The initial KE of that mass is 2058 Joules and after being slowed it is 672 Joules so the air has lost 1386 Joules of KE.

In this best case analysis I will allow for ALL of that energy to be transferred to the cart! (In reality there will be air turbulence around the propeller, and such a 100% transfer is absolutely impossible).

Now we must consider the losses: In order for the cart to generate that 1000 Joules of energy at the wheels, it must move a distance of 9 meters over the ground against the drag force that we calculated to be 174 N. 174 N x 9 meters = 1,566 Joules of energy the cart requires in order to do the work at the propeller and overcome all drag at the wheels and due to air resistance.

Now it just a simple matter of seeing if the energy taken from the air is enough to replace the energy taken from the cart’s kinetic energy to do the work at the propeller and overcome all losses. 1566 J/s needed vs 1386 J/s supplied leaves a shortfall 180 J/s.

It should be obvious at this point, to even the most devout member of the cart cult, the cart simply will not work as advertised!

 

[humber]

But he doesn't want to use it as an infinite sink for momentum.

He wants to consider the earth as simultaneously having infinite mass and having zero mass: infinite mass so that it's an inertial reference frame, and zero mass so that it doesn't apply any force to the cart (equivalently, doesn't change the cart's momentum at all).

It makes no difference, Dodge69. Do ice carts stop working because the surface is "only" a frozen lake?
The difference between the idealized planet, and this one, would be so small as to be immeasurable. The entire matter is evasion of unhindered
analysis, because the theory fails by a huge margin.


There is not one trial where there are not large cross winds.

Even the record trial is like that. What is not seen in the published chart, is that prior to launch, those same 50 degree winds are there.

The problem with the GPS direction, and its influence upon the wind direction data, hides the truth.

I have made that transparent in this chart, and removed some of the influence on the data. That can be improved, but it is already clear that that cart starts once again when the wind is moving from +50 to -50 degrees.
This thread is not a debate, but about the unmasking of fraud.

 

[fttw]

Are you also happy to assume that the momentum of the cart-plus-air is conserved?

No.

Momentum is conserved only in a closed system. Closed systems are finite; if the earth has infinite mass it cannot be part of a closed system.

Example: I sit on the cart and push myself along with a stick. I impart momentum to the cart. Where does that come from? Two answers, either of which are acceptable (but you can't mix-and-match)

EITHER: The earth is finite and the momentum that the cart-and-I gain is cancelled by an equal and opposite change of momentum of the earth.

OR: The earth has infinite mass, cannot accelerate when pushed against, and remains an inertial frame (all three exactly equivalent conditions) and functions as infinite source/sink for momentum which I transfer to the cart by pushing with the stick. Momentum is not conserved in this view but there is no violation of the "Law of Conservation of Momentum" because this system is not closed.

Either viewpoint is fine; either leads to good physics when used consistently. Switching between the two "at will" will lead to incorrect conclusions.

 

[jduffy77]

No.

Momentum is conserved only in a closed system. Closed systems are finite; if the earth has infinite mass it cannot be part of a closed system.

Example: I sit on the cart and push myself along with a stick. I impart momentum to the cart. Where does that come from? Two answers, either of which are acceptable (but you can't mix-and-match)

EITHER: The earth is finite and the momentum that the cart-and-I gain is cancelled by an equal and opposite change of momentum of the earth.

OR: The earth has infinite mass, cannot accelerate when pushed against, and remains an inertial frame (all three exactly equivalent conditions) and functions as infinite source/sink for momentum which I transfer to the cart by pushing with the stick. Momentum is not conserved in this view but there is no violation of the "Law of Conservation of Momentum" because this system is not closed.

Either viewpoint is fine; either leads to good physics when used consistently. Switching between the two "at will" will lead to incorrect conclusions.

Which is exactly what he does.