Ah. More obfuscation. Same denial. Clever of you to avoid exposure.
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Down wind faster than the wind
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Ah. More obfuscation. Same denial. Clever of you to avoid exposure.
John Freestone
Graduate Poster
Hi Humber, sorry if that was a bit confusing. The 'film' was later in the same post; it was the next bit you quoted. This:
johnfreestone said:
You responded:
I'm not sure if it was you who pointed out one of those 'true' differences that I wrote about - I think so, and I wanted to mention it, because I thought it would be nice to find one exception, something I spotted and thought, hey, that seems actually a valid point.
There are some valid differences, but they are absolutely nothing to do with a "trite reversal of vectors". As has been explained, we can choose whatever frame of reference we like, not only because some are more useful than others for practical purposes (not having to run alongside a cart measuring things; still air avoids the natural complications of real winds over land; there is the equivalent of an infinite roadway to work with), but significantly because all frames of reference are arbitrary anyway.
I concede that, in a very strict sense, successful demonstration of the cart moving forwards faster than windspeed in the treadmill, turntable or other analogous system is not precisely what was claimed, but to consider this a failure of the demonstration because of the change of frame of reference itself, rather than the true physical differences translated from one frame to the other, as I did above, (assessed also for their likely influence) is quite wrong, IMO.
If it was more practical to slam walls into cars to see what happened to crash-test dummies, the same facts could be discovered and the same developments made to safety equipment that way. There would be differences: there would not be the usual bow wave in front of the car, and a bow wave, somewhat different, in front of the wall. These are not great differences in terms of finding out facts about the massive forces involved in metal-brick-dummy collisions, and a camera attached to the moving wall would film the same scene, give or take whatever those differences cause differently, plus a moving background instead of a still one.
But it becomes an even closer equivalence if you could slam walls, moving at windspeed, into cars. Bow wave on the car? Yep. Bow wave on the wall? Nope. Same shape, pressure, etc. bow-wave on the car? Yep. What, identical? Can't be. Yep. As has been said, if you model the relevant conditions relative to each other, there is no device or divination that can discern any difference inside that system. Sure, you can step out of the system and see differences. The camera on the wall of the crash lab will still show the background moving.
I think I mentioned at one point a feature of wind moving over land, that it is faster at height, since it is slowed by the ground. Even this, in the treadmill situation, will be accurately modelled, by the treadmill dragging the air along with it in similar fashion, other than the fact that the road does not extend much beyond the sides of the cart, as I pointed out. Again, notice that the sense of the speed gradient is maintained, since the tread is advancing from in front of the cart, so it will accelerate the otherwise still air. Actually, strictly speaking, 'acceleration' is what is happening also to the wind as it moves over the land, only it's against it's current speed. Looked at from the opposite perspective, all the relative velocities are the same, other than the difference of the limits of the conditions (i.e. the volume of air to the side of the tread not being dragged backwards, but all the air across the land being dragged backwards).
I can't see that being a significant difference. I don't imagine that it makes the difference between successful modelling and failed modelling of the overland conditions.
I'm fairly confident of the above, but maybe a physicist will check it over. What kinetic energy "is in equivalency-land" is anyone's guess, since the place is in your head. Across different frames of reference, I believe kinetic energy translates to kinetic energy. I'm sure someone will tell me if I'm wrong.
sol invictus
Philosopher
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What you said is just fine. You're right that there are some differences due to the fact that the treadmill is of finite size, that the ground outside is made of something different than treadmill belt material, etc. You're equally right that these differences are irrelevant.
As for kinetic energy, it remains kinetic energy under a change of reference frame (which is called a "boost" in physics lingo), but of course its value changes. Energy is not conserved by boosts, but the equations of motion and the laws of physics are.
One final comment - humber either totally fails to understand this and is a troll or understands it, pretends not to, and is a troll. Either way don't expect to have any kind of meaningful exchange with him.
It is precisely what I claim. People often make the mistake that we are using the treadmill to "model" the real world. The fact is that the treadmill IS the real world. If there were any such thing as an absolute frame of reference, and we could show that the earth happens to be stationary in that frame, then I'd be wrong. But the reality is that all velocities are relative. The difference between the treadmill and the earth is that the earth is bigger.
Dan O.
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The evidence for the first point is the only evidence you have presented to this thread. Your claim that the treadmill is an invalid test though, assuming that you can articulate that claim and properly demonstrate it, is worthy of the Million Dollar Challenge. You shouldn't be wasting time in this thread because the MDC is set to expire soon.
Obsfuscation? That was not clear to you? Stop prevaricating.
I say that the cart will not reach windspeed, so I can hardly be avoiding that exposure.
Maybe, but you still don't have any evidence of windspeed travel.
I doubt that the treadmill is a candidate for the MDC, and I am not interested in applying. How about you? You could drive it to prove the treadmill's validity. I am sure that would be enough.
Dan O.
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I have all the evidence I need. I offer you a direct 1 on 1 challenge. I claim that the wind powered cart can travel faster than the wind pushing it and will pledge a $100 donation to JREF if proven wrong. If you back your claim that I am wrong with an equal pledge, we will proceed to contact JREF to independently test this claim.
That's a GREAT idea. I hope JREF will agree to perform the independent test. I will help out in any way I can.
Again, the claim is downwind faster than the wind. Test the claim, not your preconceived notions.
I came up with an idea of on explanatory video. I think this could "make it click" for quite a few people. The idea is not to prove anything, just to explain the way the cart utilizes the speed _difference_ and how the prop is a prop and not a turbine.
Scene 1: hold the cart up in the air and bring a fan behind it -> the propeller starts spinning CCW
Scene 2: get rid of the fan, put the cart down and slowly push it forwards -> the propeller starts spinning CW
So the wind wants both: to spin the prop CCW AND via gearing to spin the prop CW, which force will win depends on the pitch and gearing.
This has ofcourse been said and explained many times. Just had this idea how to demonstrate the idea without any math/fysics.
Scene 1: hold the cart up in the air and bring a fan behind it -> the propeller starts spinning CCW
Scene 2: get rid of the fan, put the cart down and slowly push it forwards -> the propeller starts spinning CW
So the wind wants both: to spin the prop CCW AND via gearing to spin the prop CW, which force will win depends on the pitch and gearing.
This has ofcourse been said and explained many times. Just had this idea how to demonstrate the idea without any math/fysics.
I presume you mean preconcieved notions such as not presuming the outcome of an experiment.
Marcus
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Don't you think that a treadmill is too short for a definitive test? The observed advance could possibly be accounted for by the energy stored in the device while it gets up to speed. Perhaps a homemade wind tunnel? Shouldn't be that hard for these scales and speeds.
Michael C
Graduate Poster
I just had a look at Charles Platt's proposal for a test. Spork had already said that it was ridiculous, but I wasn't quite prepared for the magnitude of ridiculosity:
Although this has nothing to do with testing the ability of the cart to run faster than the wind at constant wind speed, it has definite potentiality as entertainment. I have a suggestion for Spork and JB: accept this test, under the following conditions:
- You agree to set up the tethered cart in an appropriate place and provide a powerful battery-driven electric fan.
- Charles agrees to follow the cart with the fan. That's all he has to do, just go around the track behind the cart directing the fan towards the propeller. He may bring his own styrofoam fragments if he wishes.
Now comes the fun part: what will actually happen? Will the cart accelerate to a certain velocity and then stay at that speed indefinitely, with Charles running at the same speed behind it until he drops? Or will both cart and Charles go faster and faster until they turn to butter? Or will something completely different happen? The bets are on...
Although this has nothing to do with testing the ability of the cart to run faster than the wind at constant wind speed, it has definite potentiality as entertainment. I have a suggestion for Spork and JB: accept this test, under the following conditions:
- You agree to set up the tethered cart in an appropriate place and provide a powerful battery-driven electric fan.
- Charles agrees to follow the cart with the fan. That's all he has to do, just go around the track behind the cart directing the fan towards the propeller. He may bring his own styrofoam fragments if he wishes.
Now comes the fun part: what will actually happen? Will the cart accelerate to a certain velocity and then stay at that speed indefinitely, with Charles running at the same speed behind it until he drops? Or will both cart and Charles go faster and faster until they turn to butter? Or will something completely different happen? The bets are on...
Michael C
Graduate Poster
No, the treadmill is always long enough: just keep it going and it rolls out more surface. Look at this video where the cart runs for more than 1 minute 40 seconds on the treadmill. If the treadmill is running at around 15 km/h (I think most treadmills can manage that), 1 minute 40 seconds would correspond to more than 400 meters of road.
How are you going to make a wind tunnel that long at home?
Alrighty - I sure hope JREF will go for it. Having them as an independent arbiter will be GREAT. Let me know how I can help.
(oh - and thanks for donating $100 to JREF humber).
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Dan O.
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Then the challenge is on. First we have to come up with the terms of what will be considered a valid test. What is the objection to testing the cart on a treadmill in a room with still air?
Good!. Indoors is probably the only practical means. Measuring velocities in the wind would be difficult.
A treadmill would be suitable. I am quite happy with the circle and fan idea. As long as the fan does not track the rear of the cart so that the force between the fan and cart is artificially high, that I think that is a valid test.
Michael C
Graduate Poster
If I may, I would like to add my pledge. I also claim that the wind powered cart can travel faster than the wind pushing it. If proven wrong, I promise:
- to put a video of myself on YouTube, where I will publicly admit that I was wrong and that I have a faulty understanding of basic physics.
- furthermore, to take a beginner's course in classical mechanics at the Open University or other accredited institute of higher education.
Of course this promise only holds good if Humber pledges to do the same should he be proven wrong.