I recently watched Veritasium’s video on the Blackbird vehicle. A strange-looking thing that sort of resembles a wind turbine on a go-cart. To summarise it in case you haven’t seen the video yet, there is a cart with a propeller on it, and it’s travelling downwind. The wheels of the cart turn the propeller which creates thrust that pushes the cart along… And it can go faster than the speed of the wind.
Now if you find that hard to believe then you are not the only one, a UCLA physics professor has actually bet Veritasium aka Derek ten thousand US dollars that travelling downwind faster than the wind is not possible. There’s a contract and everything, and it was witnessed by Neil DeGrasse Tyson, Bill Nye and Sean Carrol, so some pretty big names in science there.
So I watched the video, and then for a week afterwards, my brain hurt as I grappled with the physics involved, and I wanted to make this video to share the extra steps that I used to understand how it works.
For me, I never had a problem believing that it was possible for such a cart to work, because I know that high performance sailboats tack both upwind and downwind much faster than the wind. And not only can the sailboat sail faster than the wind, but its velocity component in the direction of the wind can be much faster than the wind. I know that there is an immense amount of power in the wind, since I’ve worked in the wind energy industry for a decade. But what I didn’t understand was how it worked and why it doesn’t violate the laws of thermodynamics, and what stops it from just accelerating forever.