101–110 of 263 posts
I think these are the closest we get to moments of 'magic' in real life.
large ocean yacht racing boats can go much faster than the wind: https://www.kqed.org/science/8503/how-do-these-boats-sail-fa... Also this: "According to the World Ice Racing Circuit, ice boats can sail four to five times wind speed. In March 2009 a land sailboat reached 126 miles per hour on a dry lake bed in the Mojave Desert" from: https://www.straightdope.com/21344013/how-can-racing-yachts-... I think I read some…
The difference here is that the vehicle in the article is traveling parallel with the wind
Imagine two sailboats on a cylindrical ocean on diagonal tacks, on opposite poles, and rotating around the core with rods connecting them to the core. Now you have a propeller. :)
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Then what is spinning the wheels?
The wind, I think. My current impression is that when it is starting, the whole thing is basically just acting as a big sail. You could lock the propeller and prevent it from spinning and it would still move forward. After that is where I start to get more fuzzy on the matter. On the one hand it makes sense that by using some of the speed from the wind to do other things, you can extract more total energy from the wi…
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Not an expert, but I'm going to say no. There is no medium in space, moving relative to the solar wind, against which the "keel" of a solar sail ship could push.
Gravity? I guess something with enough mass to use gravity might be too large to use solar sails.
There is some work on the idea of using both a photon sail and a magnetic sail on a single vessel. In many interesting locations, these would push in different directions, allowing you to sail.
At a standstill, the wind just acts on the entire vehicle including the stationary propeller, and sets the whole thing in motion.
Without the propeller, going directly downwind would be limited by the speed of the wind acting directly on the vehicle which otherwise lacks any relevant moving parts for the wind to act on.
By adding the propeller, driven by the forward motion via the wheels, a part of the vehicle now moves backwards (imagine the cross-section of a propeller blade as it spins, its intersection with the wind travels backwards into the wind) to compensate for the forward movement, giving the wind something to act on even when the vehicle travels faster than the wind.
The most surprising thing here is that someone on Twitter made a bet, lost the bet, and then actually paid said bet. Playing devil's advocate here a little: The whole machine is very counter-intuitive, and I can see how I myself may disbelieve it if not for the irrefutable demonstration(s)[0]. [0] https://www.youtube.com/watch?v=yCsgoLc_fzI
It's not at all counterintuitive. It's just poorly explained. Energy is 1/2mv^2, and momentum (related to force) is mv. Anytime you have different speeds, you can arbitrage. If I am pushing against still air, I can generate nearly-infinite force for arbitrarily little energy. That's why you use wings instead of pointing jet engines downwards. You push a lot of air by a little bit (lots of mv, not a lot of 1/2mv^2, si…
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I really would like a simple explanation of how that is possible. AIUI, when speed is stable, the wheels turning provide power to the propeller. But if the propeller pushes the car, which in turn makes the wheels turn faster making the car faster than the wind itself, what makes it different from perpetual motion machines? I would love a diagram showing how the power flows in this system.
Here's a simple explanation: Let's assume that the windspeed is 10 km/hr. We all agree that the wind can push this vehicle so that it is now going 10 km/hr downwind, right? From the vehicle's point of view, the wind is now 0 km/hr. But its wheels are turning, which turns the propeller, which behaves like a fan, pushing the vehicle forward in the still air, so that it is now traveling faster than the wind. This isn't…
The truth is that the car is always getting its energy from the wind, and not expending any of its own. It's just that it's been set up in a clever way that breaks our intuition. We tend to want to mentally simplify the propeller down to a disk whose motion vector is the same as that of the car. But here you've really got to think about the rotation of the propeller and the helical path its blades travel along. The wind is interacting with surfaces whose momentary motion relative to it at any given moment in time are very poorly modeled by the disk abstraction.
The most surprising thing here is that someone on Twitter made a bet, lost the bet, and then actually paid said bet. Playing devil's advocate here a little: The whole machine is very counter-intuitive, and I can see how I myself may disbelieve it if not for the irrefutable demonstration(s)[0]. [0] https://www.youtube.com/watch?v=yCsgoLc_fzI
EDIT: As an aside, I would also add that the original video did a poor job at explaining, and the demo had clear flaws which were the points the physics professor was making. More specifically, his 2 main points were
1. It's possible that when the picture of the flag was taken, the wind was slower than the car, but the car was still moving faster due to momentum
2. It's possible that the wind speed up at the propeller level is different from the ground level where the flag was
Those were both very valid criticisms, even though they didn't actually matter in the grander scheme of things.
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Having 9.5 million subscribers on a science-based YouTube channel is definitely more notable than having gone to university, or indeed having a PhD. I think the writer picked the correct description here.
I see your point, but the title and first paragraphs try to paint the picture of a "funky science" youtuber betting a UCLA physicist $10k and winning (which for me is very different to the truth: UCLA physicist bets another physicist $10k and loses)
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Having 9.5 million subscribers on a science-based YouTube channel is definitely more notable than having gone to university, or indeed having a PhD. I think the writer picked the correct description here.
It's a sad indictment of the times when people feel that having a million subscribers (read: being popular) is more notable than having a PhD (read: expert training) in a relevant field. It's no wonder anti-vaccine material is so widespread. Someone famous on Youtube said it was bad, it must be true!
I'd suggest that very few YouTubers are popular because they are popular, in fact I think this is fairly rare in general. I think it's more likely that they provide some value to their audiences. I think looking down on "celebrity culture" often fails to account for the types of value that one doesn't value themselves.