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Cake day: June 9th, 2023

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  • merc@sh.itjust.workstoScience Memes@mander.xyzMythbusters
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    10 days ago

    I’m saying that by the time the wheel is rolling, the plane’s is already moving forward

    The wheels are attached to the plane, so they move at the same time. There’s going to be slight flex due to rubber and metal not being insanely stiff, but essentially as soon as the plane starts moving forward through the air, the wheels start rolling forward along the ground. Since the conveyor belt cancels the forward movement of the wheels, the movement of the plane ceases too.

    The plane would continue accelerating even as the wheels reported weird rates of turning.

    Initially, for a few tenths of a second, or a few seconds sure. But, during that time, the conveyor belt would be moving faster and faster as it matched the speed of the wheels. The faster the conveyor moved, the more friction there would be, and the more drag there would be from that friction. Eventually you’d reach an equilibrium where the drag from the wheels was equal to the thrust from the engine, and the plane would cease moving forward. It would be exactly like the plane being anchored to the ground, except instead of a stationary anchor, the anchor would be a spinning treadmill in contact with a spinning wheel. In a world without a magic conveyor belt that could instantly adjust to the speed of the wheels, there would be some slight forward and backward movement of the plane, but that’s just like being attached to an anchor with a bungee rather than a rigid rope.

    an affixed anchor does not allow the free motion that a wheel would.

    The wheel doesn’t have free motion. By definition, the conveyor is moving at the same speed as the wheel, so the wheel is locked in place. With a real conveyor belt there would of course be some lag as the motors of the conveyor accelerated the belt, but using the hypothetical as defined, the axle of the wheel couldn’t ever move because every rotation of the wheel would be matched by a movement of the conveyor belt.

    And one of a few things happen. Either the plane has enough engine thrust to overcome the acceleration induced by the wheels, and therefore takes off, or it does not.

    The thrust would have to be infinite because, by definition, the conveyor is always going to match the velocity of the wheels. If the wheels were truly frictionless, then the conveyor belt would have no effect at all. But, any real wheel will have some friction that will increase with speed, so there will always be some speed where the force backwards from the friction of the spinning wheels matches the force of the engine.

    As an aside, my guess is that most real airplane wheels would probably fail pretty quickly at just double the normal takeoff / landing speed. The centripetal force acting on the spinning parts of the wheel and tire increase with the square of the velocity, so 2x as fast means 4x as much force. 3x as fast and 9x as much force. So, if you did this with a real wheel, you’d destroy the wheel pretty quickly. Of course, the same applies to the conveyor belt, but I’m going to assume that it’s specially engineered to survive this challenge.

    the wheels would continue spinning in increasing RPM until the plane begins moving backwards

    The plane wouldn’t move backwards because if the wheels slowed down, the conveyor belt would slow down too. Of course, that’s in a world where the conveyor belt could adjust its velocity instantaneously, but for this thought-experiment you can say that if the pilot cuts the engine or something, the wheels don’t spin as fast, so the conveyor belt slows down, and the plane remains in one spot.

    eventually it would take off anyhow. because the airflow over the wings would still generate lift

    In the thought-experiment world, there wouldn’t be any airflow over the wings because the plane would be stationary. In reality, there would be some airflow due to the movement of the conveyor belt, but the wheels would probably melt long before that was enough air to give the plane lift while stationary relative to the world around.


  • merc@sh.itjust.workstoScience Memes@mander.xyzMythbusters
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    10 days ago

    Just to clarify; you understand that because the engines are pushing on the plane itself and not the wheels, by the time the wheels start moving, the plane is already moving relative to ground and air alike.

    The wheels are attached to the plane so they move at the same time as the plane. But, I get what you’re trying to say, that the wheels are effectively being dragged by the plane, they’re not powering the movement. But, what you need to think about is that if you oppose that dragging by moving the conveyor belt in the opposite direction you can prevent the plane from moving at all. Yes, the wheels are merely dragging and there isn’t a lot of friction there, but friction increases with speed. And, if you move the conveyor belt fast enough, you can stop the plane from moving relative to the ground, which can stop it from moving relative to the air, which can prevent it from taking off.

    An anchor sufficient to keep the plane from rolling forward is different because the force it is apply is significantly greater.

    No, by definition it’s the same. The conveyor moves with however much speed is necessary to stop the forward motion of the plane. The conveyor would eventually go so fast that it generated enough force to stop the plane from moving, so it’s indistinguishable from an anchor.

    Sure, you can deflate the tires and increase the rate of spin on the wheels.

    You don’t need to deflate the tires, you merely need to increase the speed at which the conveyor moves to match the speed of the wheels.

    if we assume the wheels are indestructible, which I’d argue is only fair, then even if what you’re saying is true and we ramp up the drag induced by the wheels sufficient to counter the engines… then the wind generated by the rolling treadmill would be producing a sufficient headwind for the plane to take off

    That seems like an unfair assumption because you’re assuming that the conveyor belt has second-order effects on the air (i.e. generating a “wind” over the wings of the plane), while ignoring the second-order effects the conveyor would have on the wheels (massive heat from friction leading to failure).

    On the other hand, this entire conversation assumes the thrust to weight ratio is less than 1. If it’s more than one, well they just…. Go straight up.

    I mean, the discussion is of a plane, not a helicopter or a rocket. Even jet fighters with a thrust-to-weight ratio of more than 1 typically have engines that only have that ratio once they’re at high speed, not from a standing start. That’s why even fighter jets on carriers need a catapult-assisted takeoff. A VTOL aircraft like a Harrier wouldn’t need that, but then its takeoff speed is zero, and the myth isn’t very interesting when the conveyor belt doesn’t move.


  • merc@sh.itjust.workstoScience Memes@mander.xyzMythbusters
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    11 days ago

    If the conveyor moves at the same speed as the wheels, it is exactly like attaching an anchor. That isn’t the myth they were testing, but it’s a more interesting myth.

    it can’t do that through the wheels- the wheels can only apply a force equal to their rolling resistance and friction in its mechanics.

    It can do that if it can spin the wheels fast enough. Picture the ultra-light airplane from the episode with big, bouncy wheels and a relatively weak propeller. If the treadmill was moving 1000 km/h backwards, that little propeller could never match the force due to rolling resistance from the wheels.


  • merc@sh.itjust.workstoScience Memes@mander.xyzMythbusters
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    11 days ago

    The tricky bit is that the air within a few millimeters of the treadmill will move with the treadmill. The air slightly above that will be slightly disturbed and also move a bit in the direction of the treadmill. If you had an extremely long and extremely wide treadmill (say the length and width of a runway) it’s possible that the air at the height of the propeller would be moving along with the treadmill, rather than staying still, or moving with prevailing winds.

    But, even in that case, the plane could still take off. All the plane needs to do is move the body of the plane through the air at enough speed to allow the wings to start generating lift. If the air at propeller-height is moving with a treadmill that is moving at take-off speed, the plane might take off with zero forward speed relative to the non-treadmill ground. But, as long as you’re not somehow preventing the propeller from moving the plane through the air, the plane will always be able to take off.

    There are videos of planes taking off by themselves in high wind, and videos of VSTOL (very short take-off and landing) planes taking off and landing using only a few metres of runway.


  • merc@sh.itjust.workstoScience Memes@mander.xyzMythbusters
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    11 days ago

    at what point does this become true?

    It’s always true.

    A stationary aeroplane on a treadmill will obviously move with the treadmill

    What do you mean? The plane has its parking brakes on and moves with the treadmill surface? If you don’t have parking brakes engaged and start up a treadmill under a plane, the plane’s wheels will spin and the plane will stay pretty much in one place. Because the wheels are free to spin, initially that’s all that will happen. The inertia of the plane will keep it in place while the wheels spin. Over time, the plane will start to drift in the direction the treadmill is moving, but it will never move as fast as the treadmill because there’s also friction from the air, and that’s going to be a much bigger factor.

    I assume an aeroplane moving at like 1 km/h still gets pulled backward by the treadmill.

    Moving at 1 km/h relative to what? The surface of the treadmill or the “world frame”? A plane on a moving treadmill will be pulled by the treadmill – there will be friction in the wheels, but it will also feel a force from the air. As soon as the pilot fires up the engine, the force from the engine will be much higher than any tiny amount of friction in the wheels from the treadmill.

    but how does it get lift if it is prevented from accelerating from 0 to 1 km/h of ground speed

    It isn’t prevented from accelerating from 0 to 1 km/h of ground speed. The wheels are spinning furiously, but they’re relatively frictionless. If the pilot didn’t start up the propeller, the plane would start to move in the direction the treadmill is pulling, but would never quite reach the speed of the treadmill due to air resistance. But, as soon as the pilot fires up the propeller, it works basically as normal. A little bit of the air will be moving backwards due to the treadmill, but most of the air will still be relatively stationary, so it’s easy to move the plane through the air quicker and quicker until it reaches take-off speed.


  • merc@sh.itjust.workstoScience Memes@mander.xyzMythbusters
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    11 days ago

    I think the confusion is that the conveyor belt is running at a fixed speed, which is the aircraft’s takeoff speed. That just dictates how fast the wheels spin, but since the plane generates thrust with its propeller, the wheels just end up having to spin at double takeoff speed. Since they’re relatively frictionless, that’s easy.

    The more confusing myth is the one where the speed of the conveyor belt is variable, and it always moves at the same speed as the wheels. So, at the beginning the conveyor belt isn’t moving, but as soon as the plane starts to move, and its wheels start to spin, the conveyor belt movies in the opposite direction. In that case, the plane can’t take off. That’s basically like attaching an anchor to the plane’s frame, so no matter how fast the propeller spins, the airplane can’t move.




  • merc@sh.itjust.workstoScience Memes@mander.xyzAcademia to Industry
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    14 days ago

    PhD level intelligence? Sounds about right.

    Extremely narrow field of expertise ✔️
    Misplaced confidence in its abilities outside its area of expertise ✔️
    A mind filled with millions of things that have been read, and near zero from interactions with real people✔️
    An obsession over how many words can get published over the quality and correctness of those words ✔️
    A lack of social skills ✔️
    A complete lack of familiarity of how things work in the real world ✔️


  • merc@sh.itjust.workstoScience Memes@mander.xyzIron
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    2 months ago

    Do you mean just the edge? Because with a sword basically the whole thing other than the handle is the blade.

    But yeah, with a tiny diamond edge you’d probably have the best of both worlds, a light, flexible sword with an ultra-sharp cutting edge.

    Still, the edge probably wouldn’t last for long. If the diamond was attached to a steel blade and the blade flexed, the diamond couldn’t flex and would probably snap.




  • merc@sh.itjust.workstoScience Memes@mander.xyzVoyager 1
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    2 months ago

    To me, the physics of the situation makes this all the more impressive.

    Voyager has a 23 watt radio. That’s about 10x as much power as a cell phone’s radio, but it’s still small. Voyager is so far away it takes 22.5 hours for the signal to get to earth traveling at light speed. This is a radio beam, not a laser, but it’s extraordinarily tight beam for a radio, with the focus only 0.5 degrees wide, but that means it’s still 1000x wider than the earth when it arrives. It’s being received by some of the biggest antennas ever made, but they’re still only 70m wide, so each one only receives a tiny fraction of the power the power transmitted. So, they’re decoding a signal that’s 10^-18 watts.

    So, not only are you debugging a system created half a century ago without being able to see or touch it, you’re doing it with a 2-day delay to see what your changes do, and using the most absurdly powerful radios just to send signals.

    The computer side of things is also even more impressive than this makes it sound. A memory chip failed. On Earth, you’d probably try to figure that out by physically looking at the hardware, and then probing it with a multimeter or an oscilloscope or something. They couldn’t do that. They had to debug it by watching the program as it ran and as it tried to use this faulty memory chip and failed in interesting ways. They could interact with it, but only on a 2 day delay. They also had to know that any wrong move and the little control they had over it could fail and it would be fully dead.

    So, a malfunctioning computer that you can only interact with at 40 bits per second, that takes 2 full days between every send and receive, that has flaky hardware and was designed more than 50 years ago.


  • I mean alledgedly ChatGPT passed the “bar-exam” in 2023. Which I find ridiculous considering my experiences with ChatGPT and the accuracy and usefulness I get out of it which isn’t that great at all

    Exactly. If it passed the bar exam it’s because the correct solutions to the bar exam were in the training data.

    The other side can immediately tell that somebody has made an imitation without understanding the concept.

    No, they can’t. Just like people today think ChatGPT is intelligent despite it just being a fancy autocomplete. When it gets something obviously wrong they say those are “hallucinations”, but they don’t say they’re “hallucinations” when it happens to get things right, even though the process that produced those answers is identical. It’s just generating tokens that have a high likelihood of being the next word.

    People are also fooled by parrots all the time. That doesn’t mean a parrot understands what it’s saying, it just means that people are prone to believe something is intelligent even if there’s nothing there.

    ChatGPT refuses to tell illegal things, NSFW things, also medical advice and a bunch of other things

    Sure, in theory. In practice people keep getting a way around those blocks. The reason it’s so easy to bypass them is that ChatGPT has no understanding of anything. That means it can’t be taught concepts, it has to be taught specific rules, and people can always find a loophole to exploit. Yes, after spending hundreds of millions of dollars on contractors in low-wage countries they think they’re getting better at blocking those off, but people keep finding new ways of exploiting a vulnerability.


  • Yeah, that’s basically the idea I was expressing.

    Except, the original idea is about “Understanding Chinese”, which is a bit vague. You could argue that right now the best translation programs “understand chinese”, at least enough to translate between Chinese and English. That is, they understand the rules of Chinese when it comes to subjects, verbs, objects, adverbs, adjectives, etc.

    The question is now whether they understand the concepts they’re translating.

    Like, imagine the Chinese government wanted to modify the program so that it was forbidden to talk about subjects that the Chinese government considered off-limits. I don’t think any current LLM could do that, because doing that requires understanding concepts. Sure, you could ban key words, but as attempts at Chinese censorship have shown over the years, people work around word bans all the time.

    That doesn’t mean that some future system won’t be able to understand concepts. It may have an LLM grafted onto it as a way to communicate with people. But, the LLM isn’t the part of the system that thinks about concepts. It’s the part of the system that generates plausible language. The concept-thinking part would be the part that did some prompt-engineering for the LLM so that the text the LLM generated matched the ideas it was trying to express.