A YouTuber bet a physicist $10k that a wind-powered vehicle
businessinsider.com
businessinsider.com
It says: "Blackbird is unique because it can move directly downwind faster than the wind itself for a sustained period. Any sailor worth their salt can tell you that a boat can do that by cutting zigzag patterns; that's called tacking. But the idea that a vehicle can beat the breeze traveling straight downwind, no tacking involved, is controversial."
Sailboats travel _upwind_ by tacking, not downwind and measured by forward progress it's significantly slower than the wind speed because the extra distance travelled.
Sailboats can travel directly downwind however because hull speed is a thing, only crazy racing boats with hydrofoils so much as approach a significant fraction of wind speed.
2) Hull speed is a limitation for displacement sailboats. Sailboats that plane or use hydrofoils or have long skinny hulls (e.g. catamarans) do not have the hull speed limitation of a displacement hull.
While the article uses sailboats as their sailing example, a much better example would be iceboats[2] which have extremely low friction. They can go up to 10x the speed of the wind. According to google, the record is 143MPH.
Iceboat racers definitely tack downwind and definitely go faster than the wind by jibing ("tacking") downwind.
The key to understanding the "faster than the wind" car is to realize that, because the propeller is spinning, the apparent wind for the propeller is no longer coming from directly behind the car. The propeller is cutting across the wind and thus the apparent wind is coming at an angle "across the car". (Since the propeller is spinning in a circle, it never has to jibe - iceboats have to jibe because otherwise they would run out of ice.)
[1] Technically sailboats will jibe rather than tack downwind. Tacking is when you pivot the bow into the wind, jibing is when you pivot the bow away from the wind.
"If there is two mediums moving at different speeds, we can harness this energy gradient to do stuff, like moving some objects at some speed. And those three speeds have nothing to do with each other, the generated speed can very well be greater than first two, if the energy harvested is greater than energy needed."