Hello, Greg. The treadmill is the basis of the windspeed claim and offered as evidence,
But you don't need a treadmill to prove or disprove the theory of how the cart works or that it works, right? Someone here must have posted the "parachute pulling a yoyo" drawing already, I assume. It's on page 9 of my document. Other folks have made their own drawings of it.
You can build it with two paper plates, an empty soda can, some string, and some tape. And then pull on the string and watch the yoyo move faster than teh string. And there's no treadmill involved.
but I say the treadmill itself is false,
there may be minor differences in the exact airflow between on-the-ground and on-the-treadmill.
and therefore can say nothing either way about the cart. That is easily dismissed from a physical point of view, but its claims are supported by ideas that are metaphorical. That makes it difficult to knock down.
models are useful for simplifying reality. They throw out some aspects of reality so that our computers or our small scale model or our test case remains managable. And while a model may not be exactly the same as reality, they can produced results that are useful in the real world.
That cart itself is a 'simple' Newtonian device,
The cart is a "simple machine". Basically, its a block and tackle. See page 13 of my document. If you want to break it down into smaller simple machines, the propeller is a "screw", there's a "wheel and axle", and the right-angle gear box are basically two "screws" working together. But the overall effect of all the different gear ratios from air to prop, prop to shaft, shaft to gearbox, gearbox to axle, axle to wheel, wheel to ground, is that the cart acts like a block and tackle.
The difference is that most block and tackles are designed to reduce the amount of force you need to move an object by increasing the amount of distance you need to exert that force. you might have a block and tackle set up to hoist a 1000 pound weight. And at the end of the rope you're holding, you only have to exert 20 pounds fo force. But to move the weight 1 meter, you'd have to reel in 50 meters of rope.
work = force * distance
1000 lb * 1meter = 20 lb * 50 meter.
THe work you put in is the work you get out.
The cart sets up the block and tackle not to reduce the force needed by increasing the distance you pull the rope, but instead to reduce teh distance you need to pull the rope by increasing the amount of force you need to exert on the rope.
With the parachute-pulling-a-yoyo, the wind pushes on the parachute and moves it 5 meters, and the parachute pulls on the rope wrapped around the yoyo axle, moving the yoyo 10 meters. To do this, the cart has to cut the force from the wind in half by the time it acts on the yoyo. If the wind exerts 10 newtons of force, the cart only has 5 newtons of force to work with to overcome friction and to accelerate the cart via f=ma.
and nothing to do with "frames of reference".
You don't need to understand inertial frames to get that the cart can go DDFTTW. THe parachute pulling a yoyo idea is one way to see how a vehicle can go DDFTTW without a treadmill.
I think DDFTTW is perhaps possible,
It is.
but this approach looks to me like it would need to break a few physical laws on the way.
Well, the thing about using a video to prove something is that videos can be faked. Magicians use slight of hand to make you think something happened that actually didn't. I read an article about scientists versus charlatans somewhere and it was saying that your average scientist isn't good at catching charlatans because the scientist will believe their eyes when combined with the narrative from the charlatan and conclude exactly what the charlatan wants them to conclude. The article went on to say that catching charlatans is actually its own specialization in science.
And of course, pretty much everyone's interoduction to the DDFTTW idea is from a video clip on youtube, with someone attempting to demonstrate a cart. Good science isn't just a visual demo by some anonymous guy on the internet. And a high dose of skepticism is called for.
But if you set aside the video demonstrations (cause video can be faked) and you set aside the issue with the treadmill (because the treadmill isn't needed to build a cart or understand how it works) and instead look at the theory of the cart, as a simple machine, a block and tackle, you should be able to see that its possible to pull on a rope at 5 meters per second and have some other object move at 10 meters per second, and do so by reducing the force exerted.
