Tuesday, August 10, 2021

Going With the Wind, A Twitter Story

Derek Muller started creating unique videos that are often related to physics and physics education in 2011 on his Veritasium YouTube Channel and website. I was a big fan from the start and have shown his Misconceptions About Temperature video to hundreds of teachers at my workshops. One of his recent videos, Risking My Life to Settle a Physics Debate, was very entertaining but I did not pay close attention to it. In it Derek recreates an accomplishment that was originally done by Rick Cavallaro and John Borton. In 2010 they drove their Blackbird vehicle directly downwind faster than the wind. This is sometimes abbreviated as going DDWFTTW. In a 10 mph wind the Blackbird reached a top speed of 27.7 mph, almost 3 times faster than the wind. This feat was well documented and explained at the time. But this begs the question, why did Derek Muller title his video "Risking My Life to Settle a Physics Debate"? Although there were a few people skeptical of the 2010 achievement, if you spend some time digging into the data and documentation, this skepticism fades quickly. Unfortunately, I was not one of the people who did their homework. I watched the video with an uncritical eye. When I read on Twitter that Derek had made a bet with a physics professor, I responded with a Tweet referring to other scientific bets.


Soon after that, the physics professor who had accepted the bet, Alex Kusenko, responded to my Tweet:

This got my attention. One of the principal subjects in an ongoing social media drama had responded to my Tweet. His confidence made me question my original acceptance of the DDWFTTW success, but I was still supportive of Derek's Blackbird ride in my response.

Using Galileo's famous but apocryphal quote was a little off-base considering that there was no question that the Blackbird moved. The question was whether it could go faster than the wind when going directly with the wind. Assuming that the force of the air could get it up to the speed of the wind, how could it continue to speed up in what would be a dead calm for the person on the Blackbird? How could it extract energy from the wind to add to its kinetic energy? Alex's response linked to his presentation explaining why he thought DDWFTTW was physically impossible. You can find his presentation online but it has been updated.

After reading Alex's slides I had more questions about Derek's Blackbird ride. It seemed plausible that the wind speed decreased rapidly while the Blackbird lost speed at a slower rate, allowing it to go faster than the wind temporarily as it slowed down. I analyzed the forces and realized that Derek had left out something important in his video. He never mentioned that for the wheels to be driving the propeller, there would have to be a force of friction from the ground that opposed the motion of the Blackbird. I sent Alex a reply that shows my growing doubt. The flattery in his response may have influenced my change of mind too!

I decided to pick a side and responded to one of Derek's Tweets. Although I don't regret sending this, I wish I had left the remark about investing the $10k out, it was arrogant. This Tweet is now pinned to Alex's account so I am still paying for it!

Alex contacted me after this Tweet to discuss a project with his educational platform Kudu.com. We have had several video conferences since then but they concern a project to create an AP Physics 1 course on Kudu.com. It will be free for high school teachers and students to use. Since these conversations are not related to this post, I will not mention them further. The above Tweet also drew the attention of Rick Cavallaro, one of the inventors of the Blackbird. I was unaware of the amount of skepticism he has had to deal with and his extensive efforts to to explain how the Blackbird works. He rightfully called me out on the $10k remark.

I received this Tweet while on vacation in Colorado. I did some reading about the 2010 DDWFTTW record and realized there was a lot more to this than the Veritasium video. I discovered that there was a lot of data to indicate that it had been done before. The question was, did Derek go DDWFTTW in his video? That is what the bet was about. The video shows Derek going into the wind with a telltale indicating that the direction of the wind relative to the Blackbird is front to back. That indicates he was going DDWFTTW. If it was from a sudden gust of wind then the Blackbird would be slowing down. This is what Alex was claiming. If it was being driven by the wheels powering the propeller, the Blackbird would be speeding up. This is what Derek was arguing. I realized that if the speed of the Blackbird could be measured, the bet could be settled. Unfortunately, they did not outfit the Blackbird with sensors to measure its speed in Derek's video. I noticed radial lines on the back wheels that could be tracked with video analysis. I decided to use the video analysis in PASCO scientific's Capstone software to measure the angular speed of the wheel using these lines. I work for PASCO scientific and have Capstone installed on my computer. I downloaded the video from YouTube and found the section where the telltale indicates it is going DDWFTTW. It was difficult to analyze because the video was shot from a moving vehicle causing the wheel to move around in the frame. I asked our technical support manager at PASCO scientific, Mike Paskowitz, if he had any ideas. He suggested I track the end of the rotating line on the wheel and the center of the wheel. Capstone could calculate the difference between these 2 points yielding the y component of the radial line on the wheel. A graph of the y-component as a function of time would be sinusoidal. I could use Capstone's analysis tools to fit a sine function to it. The angular frequency of the sine function would equal the angular speed of the Blackbird. This worked pretty well and showed that Blackbird was speeding up. Because of the poor quality of the video, I hedged my conclusion when I Tweeted out my results.

I posted a Tweet showing the video and complained about the lack of data on Derek's Blackbird ride. Derek responded with an offer.

He also direct messaged me with an offer to send some high resolution video of his Blackbird ride.

I downloaded the video and we had a nice exchange of DMs. He even started following me on Twitter!

Before I could get to the analysis, Alex conceded the bet that very day. I don't know if the video analysis was the deciding factor but it did play a role. I was relieved because the video Derek sent me was not great for video analysis. The lines on the wheels were too blurry for the auto-tracking feature of Capstone to work. It is a lot of work do analyze 120 fps video manually.

I enjoyed the rest of my time in Colorado and put the Blackbird out of my mind. After returning home, Rick Cavallaro tagged me on this Tweet with a link to a video by Engineering with Rosie. It did a great job of explaining how the Blackbird could go DDWFTTW.

There were some things about the Blackbird going DDWFTTW that I had trouble explaining. For the Blackbird to speed up it needed a source of energy. If the source of energy was from the air, it would have to slow the air down to extract energy from it. But for the propeller to provide a force of thrust, wouldn't that speed the air up? Rosie's video explained this very clearly. The sketch from her video below shows how the air can speed up from the reference frame of the Blackbird yet slow down relative to the Earth's reference frame.

Rosemary Barnes' sketch expertly explained starting at 5:37 in her video

Another thing I had trouble explaining was how the Blackbird worked as a machine. Machines are used to do work on something. The work you put into a machine is always more than the work you get out of it. I thought the Blackbird was violating this because I viewed it from the perspective of the ground doing work on the wheels as the input work and the propeller doing work on the air as the output work. I realized I had this backwards. The Blackbird is a machine that uses energy from the moving air to do work on the Earth. I sent Rick a Tweet thanking him for recommending Rosie's video.

And he replied asking me if I had changed my mind. I answered in the affirmative but was still struggling with how I would explain the Blackbird to a high school physics student. That is always a good test of understanding.

Rick then sent me a Tweet with a link to a document he had recently written and a link to video of a talk he gave in San Francisco in 2017.



It is easy to see that Rick is generous with his time to help people understand how the Blackbird works. You can also tell he is a little peeved at Alex. I had seen the video before but the document gave a very detailed example of how the Blackbird can go DDWFTTW. If I was still teaching I would invite him to give a talk to my physics students. I then got around to re-doing the video analysis using the 120 fps video Derek sent me. It was still too blurry for auto-tracking to work so I analyzed less than 2 seconds of motion. The data came out much cleaner and still showed the Blackbird speeding up while going DDWFTTW.

Here is the video from the above Tweet:

 


I was surprised when he sent me a direct message the next day with an offer to talk on the phone.

I enthusiastically agreed and benefited from his knowledge and ability to explain things. He also listened to my thoughts and helped clarify them. I expressed my disappointment in some of his comments about Alex's concession of the bet. However, I told him I understood his impatience with those of us who were skeptical of something that had been well-documented in 2010 and had a sound foundation in the laws of physics. It is similar to when those who helped land people on the Moon hear from the idiots that say it was a hoax. The difference is we sought out the facts and admitted we were wrong.

Later that day Derek released his sequel to the his first Blackbird video. In it, Derek takes responsibility for the shortcomings in the first video including an incomplete explanation and lack of data. That was big of him but as I stated earlier, the primary shortcoming was the lack of effort to research on the part of those of us who expressed skepticism. The first video and the information posted elsewhere about the 2010 record-breaking run by Rick Cavallaro and John Borton were sufficient to win the bet. However, the second video is so good that I am glad Derek felt it was necessary to make. I remember feeling a little better when the video revealed that Bill Nye also was skeptical. He showed some of that skepticism earlier in a Tweet:

In the video Derek shows an email from Bill Nye where he says "I am pretty sure the inventors of the Blackbird are fooling themselves, or us, or both --- and, I was not thinking critically when I watched your video." This reminded my of my Tweet quoting Feynman about how easy it is to fool yourself. Here was a former engineer who also had convinced themself that the Blackbird could not go DDWFTTW. I wanted to link to this part of the video but when I watched it again, the Bill Nye email was gone! I started to doubt that I had seen it when I did a search and found the Tweet that preserved the email in a screen capture. Apparently Bill Nye asked Derek to remove this from his video. That is too bad. Being wrong and showing when others are wrong is crucial for the advancement of science and engineering. A person who goes by the moniker "The Science Guy" should not hide their mistakes.

Another part in the second video that stood out for me is the video analysis of Derek's Blackbird run. They edited the video to track the center of the wheel so that it remains fixed in the frame. They added 2 color bars to show the rotation, making it easy to see that the Blackbird is speeding up while going DDWFTTW.

 


At 8:43 in the second video Derek mentions that it was "someone on Twitter" who suggested doing video analysis. I thought that could be me so I asked Derek about it in a DM.


He confirms it, sort of. So I can claim I was mentioned in a Veritasium video. One more thing crossed off my bucket list! Now all I have to do is find the time to make the model of the Blackbird that Xyla Foxlin describes in her YouTube video. Click on the "SHOW MORE" link at the end of the video description for details. Thanks for reading my self-indulgent story. It is over except for the notifications I keep getting whenever someone likes one of the redundant replies to my Tweet pinned to Alex Kusenko's Twitter account. At least onr part of it never ages: "The first principle is that you must not fool yourself — and you are the easiest person to fool."- R. Feynman






5 comments:

JB said...

Hi Dan. I'm John "JB" Borton, Rick's partner in the Blackbird adventure.

What a great write-up. Thanks. My Step-daughter was your student at Los Gatos many years ago and I always loved your creative approach to science education.

Given that I knew you and your reputation, I was a bit bummed to read some of your early posts, but I did write publicly during it all "Dan is a good guy -- he'll get it."

Btw, Rick is as passionate and creative as you about science education and I've literally never seen anyone better at explaining science/mechanics/etc. than he is. You two should work together if you get the chance.

Thanks again
JB

Anonymous said...

The video analysis was also suggested by Taus Møller:

https://twitter.com/teaamoeller/status/1407002674835472384

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Michael Cook said...

Hi Dan, thanks for telling that story. I really appreciate your intellectual honesty: the mark of a true scientist and a true teacher. I think we all need to somehow pin that Feynman quote to a prominent corner of our minds where it will always be there to remind us how easily we can fool ourselves.

An amusing thing: one of the links on this page is to Rhett Allain's blog on Wired. Rhett was one of the prominent nay-sayers way back in 2008. He posted on his blog, dismissing travelling downwind faster than the wind as clearly impossible: "This is the same situation as people trying to make energy from nothing." See: https://www.wired.com/2008/12/physics-and-directly-downwind-faster-than-the-wind-dwfttw-vehicles/

He even ended his blog with "Dear MythBusters. When you do an episode on this topic, please mention my blog. It will make my kids think I am cool." After some more blog posts and a lot of discussion in the comments, he must have realised that he was wrong, but never clearly admitted it. Instead he did some hand-waving and finally (a couple of years later, when people were still annoying him about it) came up with this: "I will not discuss the physics because it doesn't really match with my agenda for this blog." See https://scienceblogs.com/dotphysics/2010/05/31/why-would-i-think-that

What a pity: as you say when talking about Bill Nye, "Being wrong and showing when others are wrong is crucial for the advancement of science and engineering." I shall pin that somewhere as well. Thanks again!

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