Down wind faster than the wind

[CNY_Dave]

The cart operates in the differential motion between 2 mediums: a hard flat surface sometimes referred to as a road or a belt and a gas referred to as the air or wind.

If the difference in velocity between the two mediums is the same, what measurment can you make to differentiate between being on a treadmill or a road?

Well, I asked 2 questions- the 1st was about the range of speeds on the treadmill (an emulation for different wind speeds), and if the range of speeds where it worked was narrow or wide, quite a valid question, and one which does not call into question any of the basic mechanisms.

The 2nd question is also perfectly appropriate because its all well and good to say the 2 cases are equivalent in analysis, but there's nothing like an actual experiment to see what happens.


Dave

 

[Dan O.]

Well, I asked 2 questions- the 1st was about the range of speeds on the treadmill (an emulation for different wind speeds), and if the range of speeds where it worked was narrow or wide, quite a valid question, and one which does not call into question any of the basic mechanisms.

The maximum speed of the cart if there were no friction to slow it down would be a fixed multiple of the wind speed over the surface. Friction slows the cart down so at low wind speeds the cart cannot keep up with the wind and at higher wind speeds the cart travels faster than the wind. For each cart there will be a specific wind speed where the cart travels at exactly the speed of the wind. It is this speed that is easiest to examine on the treadmill because the cart stays in place instead of running off the end. Another way to change the balance is to elevate one end of the treadmill so gravity adds an additional force or to add a tether to supply the restraining force.

The 2nd question is also perfectly appropriate because its all well and good to say the 2 cases are equivalent in analysis, but there's nothing like an actual experiment to see what happens.

It's all well to run random experiments because it is the experiments that produce unexpected results that lead to new theories and a better understanding of the universe. However, this experiment has been done and one in particular (Michelson-Morley^WP) was an absolute failure that led to the development of relativity theory.

 

[sol invictus]

It's all well to run random experiments because it is the experiments that produce unexpected results that lead to new theories and a better understanding of the universe. However, this experiment has been done and one in particular (Michelson-Morley^WP) was an absolute failure that led to the development of relativity theory.

We don't need Michelson-Morley. We don't need Einstein, or special relativity. Forget the 20th century. Forget the 19th century. Forget the 18th century. By the early 17th century physicists understood the relevant principle here, which is called Galilean relativity for a reason.

Newton's laws are a special case of a theory of physics that is consistent with that general principle. If Galilean relativity is wrong, Newton was wrong. If Newton was right, GR is right. That's all there is to it.

If you want to know how Galilean relativity relates to special relativity, that's probably a topic for another thread (although the answer is quite simple).

 

[CNY_Dave]

The maximum speed of the cart if there were no friction to slow it down would be a fixed multiple of the wind speed over the surface. Friction slows the cart down so at low wind speeds the cart cannot keep up with the wind and at higher wind speeds the cart travels faster than the wind. For each cart there will be a specific wind speed where the cart travels at exactly the speed of the wind. It is this speed that is easiest to examine on the treadmill because the cart stays in place instead of running off the end. Another way to change the balance is to elevate one end of the treadmill so gravity adds an additional force or to add a tether to supply the restraining force.




It's all well to run random experiments because it is the experiments that produce unexpected results that lead to new theories and a better understanding of the universe. However, this experiment has been done and one in particular (Michelson-Morley^WP) was an absolute failure that led to the development of relativity theory.

I would say there are 2 treadmill speeds at which the cart will stay in a fixed position- too slow, and fast enough that drag on the prop surfaces start becoming significant.

Anyway, its just my desire to twiddle the knobs that's driving these questions at this point. Looking at the range of speeds I would call a random experiment, just to satisfy my curiosity at which speeds which effects become dominant.

Running the cart on the treadmill at a speed that the cart has run in the open I would certainly not call a random experiment, though. I would call it rather expected and basic. I'm sure someone's done it, but I haven't found that particular bit as yet, and am just looking for a link if anyone knows someone who's done it.


Dave

 

[mender]

The small cart will reach wind speed (stationary on a level treadmill) at 2.7 mph. At 10 mph treadmill speed, the 169 gram cart will remain stationary on a 4.4 degree incline, indicating a force imbalance in the forward direction of about 13 grams - enough to accelerate the cart at about 2.47 ft/sec2 if it was at 10 mph on a level road in a 10 mph wind. Once above the break-even speed, the cart will get closer and closer to it's theoretical advance ratio as the wind speed increases. It will always be above the wind speed once the wind speed gets past the break-even point.

Jack Goodman's cart has a break-even speed of 4 mph, and Mark C's cart (which spork and JB copied and refined) has a break-even speed of 8.5 mph. I don't know if Mark C's treadmill was level or inclined - can't remember.

In this article, Jack measured his cart's performance on the treadmill. He was also kind enough to send me the results of each 1 mph interval between 4 and 10 mph so that I could graph them.

http://www.ayrs.org/DWFTTW_from_Catalyst_N23_Jan_2006.pdf

His cart will easily start and roll down a one inch in ten foot incline. He measured the rolling resistance at 12.5 grams. At 4 mph the cart is at windspeed. At 10 mph it pulls forward with 150 grams of force. Each 1 mph step between 4 and 10 mph shows an increase in that unbalanced force of 25 grams with about 5% variation.

I suspect that there will be a range in which the cart will achieve the highest multiple of wind speed based on the efficiency of the drive train and propeller. I'm not sure about an ultimate top speed, because as the wind speed increases, the energy available also increases. The limiting factor would likely be the traction of the drive wheels.

 

[spork]

I'm hoping to see if someone has run the treadmill over a range of speeds to see what the lowest treadmill speed is that the cart will advance at, and the highest speed. Just for curiosity's sake, obviously there's some speed below which it'll fall back (low prop efficiency), and above some speed it'll fall back (tip drag and turbulence on the prop).

Our treadmill has a top speed of 10 mph. JB has a professional treadmill, but it also has a top speed of 10 mph. We assumed from that that it's uncommon to find a treadmill that goes faster.

JB's cart will just keep up with the treadmill at 2.7 mph. Up to 10 mph it does better as the treadmill goes faster. We have no way of knowing the top speed with our given equipment. Perhaps this is another good reason for the turntable test.

Our original cart would just barely advance on the treadmill at 10 mph. It would not advance at any lower treadmill speed.

EDIT: Looks like Mender beat me to it - and with more info.

 

[CNY_Dave]

Mender, spork, thx-

Dave

 

[huh34]

Up to 10 mph it does better as the treadmill goes faster. We have no way of knowing the top speed with our given equipment. Perhaps this is another good reason for the turntable test.

Do you have any idea of what would it actually be that "in real life" prevents the cart achieving something like lightspeed if we just increase the wind indefinately?

I think the rolling resistance is quite constant regargless of speed, right? At least it will not increase faster than the power input? The drag from the cart frame doesn't increase faster than the increase in the power input either, right?

Will the cart melt due to heat from friction?

 

[Dan O.]

I would say there are 2 treadmill speeds at which the cart will stay in a fixed position- too slow, and fast enough that drag on the prop surfaces start becoming significant.

There is another breaking point: The thrust produced by the propeller is not in line with the traction on the road. At some speed this torque will be sufficient to flip the cart over its front wheels.

 

[Michael C]

Do you have any idea of what would it actually be that "in real life" prevents the cart achieving something like lightspeed if we just increase the wind indefinately?

The usual stuff that prevents any vehicle on Earth from attaining speeds near to the speed of light. If we neglect all unwanted friction, air drag and relativistic effects, we can make the thing theoretically go at any multiple of wind speed, just as we can make a car theoretically go any speed we like simply by increasing the gearing ratio.

 

[Marcus]

The ground reference is special because it IS common.

Not true. The surface of the Earth doesn't enjoy a magical status as a preferred reference frame. It is no better or worse than any other.

 

[spork]

Do you have any idea of what would it actually be that "in real life" prevents the cart achieving something like lightspeed if we just increase the wind indefinately?

I think the wheels slipping would likely be an issue. And certainly propellers become much less efficient as their tips approach mach 1. When their tips exceed mach 1 they're awful. In real life I expect the top speed would be at a more meager point as a lightly loaded airfoil is less efficient. As we get too much speed (even well below mach) the prop would be getting pretty innefficient.

There is another breaking point: The thrust produced by the propeller is not in line with the traction on the road. At some speed this torque will be sufficient to flip the cart over its front wheels.

On our little carts the thrust line does go right through the front axle. So it shouldn't produce a forward pitching moment.

 

[Marcus]

Our treadmill has a top speed of 10 mph. JB has a professional treadmill, but it also has a top speed of 10 mph. We assumed from that that it's uncommon to find a treadmill that goes faster.

JB's cart will just keep up with the treadmill at 2.7 mph. Up to 10 mph it does better as the treadmill goes faster. We have no way of knowing the top speed with our given equipment. Perhaps this is another good reason for the turntable test.

Our original cart would just barely advance on the treadmill at 10 mph. It would not advance at any lower treadmill speed.

EDIT: Looks like Mender beat me to it - and with more info.

My Smooth treadmill ( consumer type) does 12 mph.

 

[GreyICE]

Do you have any idea of what would it actually be that "in real life" prevents the cart achieving something like lightspeed if we just increase the wind indefinately?

I think the rolling resistance is quite constant regargless of speed, right? At least it will not increase faster than the power input? The drag from the cart frame doesn't increase faster than the increase in the power input either, right?

Will the cart melt due to heat from friction?

I think your issues kick in long before light speed. In fact they'd become quite unbearable around Mach 1.

Wind is not light. You can tell this because one is a wave/particle set of massless photons and one is a fluid flow.

You mistaking the two is a little... bad.

 

[spork]

Wind is not light. You can tell this because one is a wave/particle set of massless photons and one is a fluid flow.

You mistaking the two is a little... bad.

I see no evidence that anyone confused wind and light.

 

[John Freestone]

Humber is nothing but a troll. His writing is pure gibberish and doesn't deserve to be analyzed because the analysis is always invalid in his made up world (ie: tethers upset the balance so can't be used to measure force).

I think that it is only through analysing it that its falsehood shows up. If we just let him post it and didn't challenge any of it, some people might get the idea that he's the expert round here. In fact, in those times when he is fairly lucid, Humber helps the learning of others by bringing up objections that can be shown to be false. His failing to accept that doesn't necessarily hinder others.

Humber won't submit to any test we propose so now it is up to him to propose a test between his reality and ours that can be verified in the real world. Until then, he is out of the conversation as far as I am concerned.

I am quite happy for you to say that he is out of the conversation until he does provide a test. What I felt was a bit odd was your request to "everyone else" not to feed the trolls, as though asking him to provide a test was not feeding him, but others responding to him was. Even so, it's fine to ask us not to. You weren't nasty about it or demanding that we don't, and even said 'please'. I just felt that I and others were being put on one side of the equation, as troll feeders, perhaps because of the nature of our responses to him, while your asking him to provide a test was a good and helpful way to proceed. Someone else may think that asking him for a test is pointless troll-feeding, for similar reasons you don't think it's worth analysing what he says - he will keep avoiding it, or post tests with incomplete protocols and wishy-washy definitions until the end of time. I personally feel that a fairly head-on, proactive criticism of his stupid ideas, ambiguous prose and duplicitous behaviour is worthwhile at the moment.

I like your approach too (I guess you'll keep on asking for that test), and JB trying to establish clearly that Humber thinks the cart will go slower up the slope, so that he can demolish the idea with another video. I quite like Chris's idea of taking the piss by collecting Humber's "best bits" of physics. I'm glad that H'ethetheth is trying to understand his claptrap (and I'm amazed he does seem to divine some meaning from the scrambled-egg and fishtanks, though I think he's ultimately wasting his time and might eventually do the spork 'STFU'). My point was just that all of us are risking feeding the troll in order to make our various challenges, including you. Does that make sense?

 

[Christian Klippel]

What's even worse is that if humber actually proposes some kind of test, it will be designed just to make the cart fail by imposing ludicrous things. I mean, come on, read what he has suggested so far. Replacing the prop with a flywheel. Putting brakes on the cart and use them. Increase friction. Apply wind in the same direction and speed as the belt. In fact, he doesn't like that the cart does what it is supposed to do, that is, floating steady on a moving belt. He wants to do something like glueing the cart to the belt, to make it non-working.

And all that after countless posts that explained what the cart is supposed to do, why it does it and how it does it. He deliberately wants to impose restrictions and constraints that have nothing to do with the regular operation of the cart, just to make it fail so he can later go on and say "look, i said it doesn't work". It is pretty much like someone insisting that you can't test an airplane in a windtunnel, and subsequently chop of the wings prior to the test to just make it fail and claim "see, as i said, it won't fly" later.

Greetings,

Chris

 

[mender]

In regard to tests that might be proposed by Humber, we've already received a good indication of what he thinks will suffice:

This was Humber's response to my concern that his test limited all testing to below wind speed.

Let us not forget what he agreed to instead - the "Platt" test. Chasing the cart around in circles with an electric fan; that was somehow supposed to simulate the cart running outdoors and be a proper test of DDWFTTW.

 

[Christian Klippel]

Let us not forget what he agreed to instead - the "Platt" test. Chasing the cart around in circles with an electric fan; that was somehow supposed to simulate the cart running outdoors and be a proper test of DDWFTTW.

Hello mender,

yes, right. And i'd _love_ to see humber conduct this particular test. I mean, come on, some dude chasing a cart on a disc with a fan ... Falling over the cable over and over again ... That _must_ be a hell lot of fun to watch!

Greetings,

Chris

 

[spork]

In my mind it seems reasonably straightforward. He clearly fashions himself some sort of scientist. Scientific theories make predictions - or they're not scientific theories. I'm at the point of engaging him only to point out that much.

Has he abandoned the "hopping" theory? In fact has anyone read enough of his tripe to know if he has offered anything that could reasonably represent even a consistent set of ideas?