Hi huh34
The wind could also be used to make a cart run around faster than the wind in the mine. You could exploit that commercially perhaps by selling season tickets for people that wan't to watch it go.
lol. I like the idea. Health and Safety might not.
I'm still pretty dumb on energy, velocity, etc., and just trust my judgement about who's talking sense about such things and who isn't, and what I can work out from diagrams, demos, video evidence, metaphors, etc. But I think - please correct me if I'm wrong here - that one of the basic principles of the cart is that it kind of trades off torque for velocity. It uses the available energy in an economical way to increase its speed, but its gearing makes it very 'weak' in terms of torque. This again is such a basic experience for anyone who has messed about with gears or ridden a bike or driven a car, that it doesn't really require detailed maths to get it. Once again, humber is suggesting (without being too specific) that if the cart could do what he can see it doing, there's a problem with energy conservation, and we're back to "This is a woo-cart! It can't be doing it!".
I also think (and wish to be corrected if wrong) that having such a vehicle in a system does take energy out of the rest of the system. If we could pile a load of carts onto a salt flat and have them moving at half windspeed, they would have taken a certain amount of energy out of the air to do that, and presumably the air beyond them would be slowed a bit. If they're going at twice windspeed, they've taken more energy. I asked this question when I was imagining my 'pipe-racer', because there it is so much clearer that there is a just one flow of fluid (gas or liquid). If it's moving at v, and I add pipe-racers, and they're as dense as the fluid (or more dense) and move faster, then somewhere there has to be more energy added to the system to keep them going at > v. Similarly, it seems intuitively obvious that when there's a cart on the treadmill, there must be more load on the treadmill motor, just as on the salt flats there's more load on the wind.
And again, if I understand what I've heard about kinetic energy, which is what we're talking about, being relative, then there's still no real distinction between 'taking energy from the air' and 'taking energy from the ground' - right? It is natural from our earth-bound perspective to see the air behind the prop of the cart on the treadmill getting accelerated (from its initial static condition in a room) and hence it has had energy added! But since it's kinetic energy and depends on relative motion of the body in question, we can use a different frame, that of the tread for instance, and now it is decelerated. The 'still air' of the room was going at v to begin with (up-tread) and now it's going up tread a little slower. Hence, from the reference of the tread, energy was extracted by the prop to move the cart forward.
There are no commercial applications, because the cart has absolutelu no commercial value (exept the tv-ad-time mythbusters will be able to sell soon).
Possibly true, and also worth comparing this with someone (my history isn't up to saying who, or even if it happened this way round) arguing that if you put some wheels together connected by a block, and wrap some rope round them, a person can pull on the rope and lift incredible weights into the air - theoretically infinite weights, given strong enough materials and good enough pulley design. As I said to spork, there may be an inventor somewhere just wishing it were possible to get something moving relative to a fluid faster than the fluid, directly in the down-fluid direction, but his engineering training wasn't up to letting him know that it's even possible, so he discounts it.
Maybe the pulley example isn't such a good one, because it seems obvious that someone hearing of the idea would think it was obviously useful, but it's also just possible that many people didn't recognise that there were any applications because they heared "a man can lift five times his own weight" and just stopped thinking. That is 'clearly nonsense', so forget it.
Again, if I'm not mistaken, torque/force is traded with velocity, only the other way round.
It's interesting to think - if I still haven't gone wrong yet - that in a curious sense, the cart is also doing the opposite. While at a whole-cart level it goes faster but is weaker, when we consider the prop screwing through the air, it is designed to move backwards w.r.t. the cart slowly enough to keep accelerating the air. So, because of its short pitch, it works over a long time doing relatively little work, a bit like someone pulling lots and lots of rope through a pulley system so that the load can be lifted a tiny amount more with each pull.
