no worries - totally my fault for going on …
I get it now. But what we did not discuss much here is that can work both ways - wheels driving propeller and moving downwind, but also wind driving propeller driving wheels and moving upwind. And in fact the blackbird recorded a record for both modes. So it does work both ways, just not in the same wind direction.
What it comes down to is that you’d need an energy field that you use for motion. But if you want a faster vector force, you’re going to need something that exerts more relative force. By definition, dark matter is a non-starter (it literally only interacts with conventional matter gravitationally). Gravity assists are already our best actual use case:
And if anyone is actually cruising around the galaxy, I think light sails are an excellent example of this.
Also, if anyone’s gotten really good at interstellar travel, they’ve figured out how to exist stably on timescales spanning at least tens of thousands of years. Our Achilles’ heel may not be speed so much as patience.
That’s quite interesting. It makes sense, but I didn’t know they had done this.
One thing that I’d love to see one of these videos do is the treadmill experiment, but also have a fan that created a wind in the same direction as the treadmill, at the same speed. (Though I admit it would be very hard to set up well.)
This would highlight the fact that the effect depends on the differential between the ground speed and the wind speed, even when the kart is moving faster than the wind.
A craft in space powered by a solar sail cannot be used like a craft on the sea or land powered by a wind sail as there is nothing to provide a reaction force in space. DDWFTTW also requires a reaction force to drive the prop. Regular sail boats and blackbird like crafts are not so dissimilar in terms of what energy is extracted from where.
great hang - let me know when your solar sail achieves 2.8 times the speed of light.
I’m not sure what point you’re making. I said solar sails are not like wind sails. Moreover, you tend to ignore relativistic effects when considering stuff that moves at human speeds, but that’s not so easy when your get to a significant fraction of the speed of light, at which point you’d better revisit your equations.
My point is simple. A solar sail is not the same as a rotary wind cart that relies on the medium differential to move faster than the medium speed. A solar sale is more like a sailboat moving in the direction, or oblique to the solar rays. Thats all.
No, it’s nothing like a sailboat which relies on the reaction force of the water to work properly. If anything it’s more like a balloon.
Nope. What drives the yacht is the difference between airspeed (wind) and the surface it stands on. Note that this is constant as long as the wind is constant and totally unrelated to the speed of the yacht itself.
This is why given an unending racetrack, constant headwind, and an indestructible propeller and gearing (and some spherical cows one assumes) the yacht could accelerate indefinitely until Lorentz comes along and makes it even more complicated.
You’re not sure because you weren’t paying attention. You’ve got it upside down. The “windmill” (which is a misnomer) doesn’t transfer power to the wheels. The wheels of the car transfer power to the propeller, which in turn provides thrust.
It most certainly could not. It can accelerate only until the drag from air resistance balances the velocity of the vehicle. Otherwise there would be literally zero reason to make it aerodynamic.
Second day….
It ia a well documented fact in engineering that any indestructible vehicle on an infinite track does not experience any drag 
Yes!!
Yes - you are right - was distracted and missed lots of details. But I’ve now gathered the details.
However the kart does in fact work both ways - by wheels transferring power to propeller and pushing air when traveling downwind; and by propeller windmilling transferring power to wheel when traveling upwind.
The kart in fact recorded records for both modes, traveling downwind, and traveling up wind, not mentioned in the video but if you want to read more about it start with the wikipedia article.
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