This isn't specifically for humber, but if he wants to have a bash at refuting it as well, he's more than welcome. Oh, by the way, humber, I know you must be busy and all, but I'd very much appreciate learning about the pre-scientific idea "the energy of the spheres" that you said I exhumed. I couldn't find it.
I thought it might be fun to present again another scenario, which proves conclusively that moving at windspeed with a tailwind is identical to having the ground move under you. Why? Because they're both happening at the same time.
We have a windcart traveling nowhere at all w.r.t. the centre of the Earth, but pointing directly west and positioned near the equator, at a latitude where the Earth's surface is rotating round the centre of the Earth at 1000 mph. To anyone on the ground (where most of us live) witnessing it from their windproof bunker, they observe a rather unusual 1000 mph east wind, i.e. blowing from east to west, although their bunker is relatively cosy in the boundary layer. The cart is not the most efficient and doesn't acheive DDWFFTW, but just manages to maintain DDWAWS (directly downwind at windspeed). Even so, they don't see it for long, as it zooms past towards the western horizon at 1000 mph. So, the question is, is this a cart moving in real wind downwind, or a cart motionless with some ground moving west-east under it at 1000 mph? To an observer in a spaceship maintaining a position stationary w.r.t. the stary skies (and the air of the wind, of course), the whole thing could look just like a fat treadmill experiment (although the wind only has to be correct where the cart is, it doesn't have to be the same everywhere).
To do this for real with our traditional 10 mph wind, we just need a 10 mph easterly at a position about 38.2 miles south of the North Pole. It then resembles the similar turntable test in still air.
I just rather like these examples because they answer in a different way many of humber's objections. The ground is obviously the ground, so you can't say that a rubber belt isn't the same. The wind is a 'real' wind (although no definition of that term has been forthcoming, because there's no such thing as unreal wind). It brings relative velocities into perspective in a very sharp and - for most of us, I imagine - easily visualised way.
You could even imagine if the Earth didn't rotate temporarily, but have the required wind and the cart blown by it downwind. No objection, surely (apart from the obvious). Then begin the Earth rotating, very gradually, and at the same time reduce the speed of the wind (relative to our space observer) up to the scenario above.
A similar transition (but ignoring the Earth's motion altogether) from cart on a stationary treadmill, blown along (acceptable) to gradually increasing the treadmill motion as the wind drops, could be useful mental fodder for anyone interested in finding the correct answers, rather than just repeating they have identified flaws and won't say what they are.
Anyone who has got their head around what velocity means, i.e. that it is always relative (and different from acceleration), is probably well beyond these demonstrations anyway.
