That’s incredible! Maybe not coincidentally, the builder of this propeller car thing is saying it has done 2.8x windspeed.
Still from video for anyone trying to picture this:
It’s 4:30 AM. Time to put robots and propeller-cars to bed. I’ll take it up in the morning (or afternoon at this rate), thanks.
Conveyor belts are like the death of physics intuition. Conveyor belts work differently from the wind though. A conveyor belt delivers a variable amount of force via static friction to keep the point of contact moving at the same speed as the conveyor. In the example, the conveyor belt pushes harder when your generator pushes against the ground. The wind works by pushing, so it delivers a fixed force for a given ground speed, and the force is zero when your airspeed is zero. You could imagine traveling slower than the wind for a while to charge up a battery, then discharging it to go faster than the wind for a while, but that shouldn’t make you go faster than the wind on average.
https://mobile.twitter.com/Femi_Sorry/status/1406649004247638021
I’m putting pineapple on my Pizza tonight & I won’t be so dramatic about the pineapples hitting the pepperoni as its delicious.
You go for it. People are very silly to be precious about pizza, a fast food designed to stick on it whatever you fancy.
I don’t think people are actually upset about it, it just became a meme to hate on it.
I talk shit on it because I find it funny sometimes but honestly I don’t care if you eat your pizza with cum on it and you make reasonable agreements with whoever you’re sharing the pizza with. Whatever makes you happy and doesn’t hurt others.
Domino’s is still in business so I assume people like that topping okay.
Right, it’s an analogy, not an exact correspondence. The bit you’re leaving out is the propeller. If something is pushing back against the wind, then a tailwind will continue to increase the ground speed of a vehicle even if it is travelling downwind at a speed equal to or greater than wind speed. If this were not so, commercial jets would not fly faster with a tailwind, but they do. The propeller still generates thrust by the same method it always does, i.e. creating a pressure differential in front of and behind the blade.
Imagine the vehicle moving downwind at wind speed, pushed by the wind. Assuming the movement is frictionless, no energy input is required to maintain this state. With a propeller hooked up to the wheels, the propeller turns and creates a pressure differential, which is what accelerates the vehicle. The hard part to understand is how the wheels do sufficient work to drive the propeller. Recall that work = force × distance. It’s therefore possible to take some amount of work done and trade large distance and small force for small distance and large force. The propeller has less distance to travel through the air than the wheels do over the ground (because the vehicle’s air speed is less than ground speed), therefore it can apply greater force. The critical point is that what ultimately supplies the energy is the differential between wind speed and ground speed, which is independent of the speed of the vehicle.
I realise this sounds like voodoo perpetual motion stuff and it sounded crazy to me at first too, but I’ve seen a lot of physicists sign off on the physics (it was even included as a question in a Physics Olympiad) and the thing seems to work. Kusenko’s explanation of the Blackbird video he saw was that the vehicle was driven to higher speed by a gust and stayed faster than the wind when the gust died down because of inertia. But it was clocked at 27.7 mph in a 10 mph wind during an official test overseen by the North American Land Sailing Association. A gust explanation simply doesn’t work for this, I’m pretty sure the officials would have noticed a wind gust to 28 mph and it’s not like the thing has a sail, a brief gust would have little effect on it.
the explanation the youtuber gave was that the wheels turn according to landspeed, and drive the propeller. the plausible mental model for me is that the forward kinetic energy of the vehicle relative to land is being converted into thrust of the propeller. but that energy was nonetheless generated initially by the drag of the tailwind (not sure about the term here), and is being spent the entire time vehicle moves faster than wind. i’m surprised that a physicist could have missed an explanation like that, so it makes me think that perhaps the stored energy being spent down to zero means that the sustained speed is impossible.
It’s kind of interesting to try pizza from everywhere.
In South Korea, I had a bunch of different toppings on pizza. Sweet potato pizza was definitely best but kimchi pizza will definitely be the most memorable…but not for a good thing.
This reminds me of the infamous jet on a treadmill thread from 22.
It’s the same with the robot / people mover example. The robot uses the speed differential between the people mover track and the stationary ground.
One way to think of it is if the robot is on stationary ground, and using a people mover track to spin a wheel that through various gears slowly moves the robot in the opposite direction of the people mover track. I don’t think anyone would have a problem with that. But from the POV of the robot the two things are exactly the same. The robot is now moving at 10.2 mph or whatever with respect to the other medium, and in the opposite direction.
I feel like the key here might be that the wind or the people mover track are relatively limitless sources of power. If the people move track feels a little more resistance it just pushes harder. The wind doesn’t feel the prop car pushing back against it. Or if it does new wind comes along immediately to replenish the slowed wind. Or something.
It does make you wonder if this could also be applied to boats sailing downwind, assuming it’s real. A water propeller powered by the motion of the boat turns a big air propeller. Maybe the key also is friction in one medium vs. another. Could the land yacht example also work in reverse - a propeller catches the wind which drives wheels?
The McCloskey’s bought new guns, regret nothing.
For a good explanation of what’s going on, we’ll need to be careful. Probably more careful than I can be. But to start at the beginning and avoid some confusion, let’s pick a frame of reference. For the moment, let this be a frame fixed on the ground.
Then, it looks to me like there are there are four forces on the car:
The car accelerates until the net force on it is zero:
F_net= F_air + F_lift - F_drag - F_friction
If we can’t agree on something like this it’s going to be hard to make progress. (By we I mean all people everywhere talking about this.)
Even after this is resolved, I have a feeling the on-going arguments will make Monte Hall look like a tea party.
I’m still amazed I didn’t know about sailboats. It’s like when I first found out about muon catalyzed cold fusion. It’s not even controversial! But Fleischmann-Pons CF is ridiculed.
Faster than wind sailboats are real, nobody cares. Faster than wind car? No way, man!
Those both sound good to me, at least relative to pineapple. And I love pineapple. Fresh pineapple is awesome.
there is a pizza place by me owned by a South Korean lady, she has a pizza with kimchi on the menu that i’m not a huge fan of but the beef short rib one is good
Kimchi contains shrimp paste?
I guess they mean it when they say that every family in South Korea has their own kimchi recipe.
I hate pineapple and ham pizza, but love pineapple and jalapeno pizza. And I was always a “lol pineapple on pizza” guy before I tried it with jalapenos.
Shrimp of some sort is pretty standard.
And it’s on the list of ingredients for the house-made kimchi at the local Korean grocery store.
