A wind-powered car that appears to defy physics wins Youtuber $10K bet
[July 29, 2021: Josh Shavit]
Derek Muller boasts of more than 9 million followers on his Youtube channel. In his videos, Muller breaks down scientific concepts in a fun manner for his viewers.
In May, he posted a video on Blackbird, a land yacht that runs on wind power.
The Blackbird has been made by an aerospace engineer. Intriguing thing about Blackbird is that it runs faster than wind speed when travelling downwind. Now this is counterintuitive. How can a vehicle running on wind power run faster than wind when the wind is flowing in the same direction? But Blackbird apparently does.
I mean, you can tack a sailboat and technically go faster than your tailwind, but that’s basically flying along a horizontal plane. Thankfully the Veritasium channel on YouTube is here to help us understand things a bit better.
In a recent video, Veritasium’s Derek Muller headed out to the famed El Mirage dry lake bed to try to do something lots of scienticians have said was impossible for ages. The Blackbird three-wheeler (they call it a 'propeller craft') was built specifically to bring practical science to a theoretical. Is it possible for the wind to push something faster than it itself is moving? The team of Rick and Neil, who built the car, believed it was possible and set out to prove it.
You can easily see the massive big twin-blade turbine at the rear but there's a lot more going on underneath the minimalist bodywork. The wind-fuelled turbine gets the car moving and then the wheels turn a sprocket, which then pulls a chain, which then feeds back mechanical energy to the turbine, providing forward thrust.
In the video below, you can see that the vehicle is using windpower twice. Once, by simply using windpower to move downwind, and then once more because the propeller works as a fan, hitting air molecules, pushing them backwards and generating extra thrust.
The bet comes together
Blackbird is so counterintuitive, in fact, that less than a week after Muller released his video (above), Alexander Kusenko, a professor of physics at UCLA, emailed to inform him that it had to be wrong. A vehicle like that would break the laws of physics, Kusenko said.
"I said, 'Look, if you don't believe this, let's put some money on this,'" Muller said. He never thought he would hear back. However, Kusenko was equally confident. "Thanks to the laws of physics, I am not risking anything," Kusenko thought.
To Muller's surprise, Kusenko actually accepted the bet and subsequently sent him airtight documents to codify the wager.
The stage was set!
There were scientific arguments and counter-arguments from both sides. This went on for weeks after which Muller decided to conduct an actual field test.
The data collected showed that the vehicle travelled at 45 km/hr when wind was flowing at 16 km/hr in the same direction. And the increased speed was not due to sporadic gust winds as the vehicle held the speed for two minutes.
So who won the bet?
After three weeks of debate, Kusenko acknowledged that Blackbird could go slightly faster than the wind, but he maintained that it was for only short periods. If a gust of wind sped up the land yacht and then quickly died down, he said, it would appear that Blackbird was traveling faster than wind.
"The resolution of our bet was not as clean as I'd hoped," Muller said. "Kusenko coughed up the 10 grand, let's leave it at that."
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