• ab60753@lemmy.zip
    68·
    16 天前

    Edit: accedentally used the wrong density. Should be the desity of the surounsing medium (air) at 1.23 kg/m3- density of helium making it slightly more fesable. I.e. i was wrong on almost an order of magnitude, but its still infeasable… thanks @exasperation, @noneofyourbuissness

    So… hear me out. Yes i know its just a comic… im just autistic. Soooo…

    Assuming the guy is average weight (70 kg) the total force of gravity on him is Fg=70×g N. The force of boyancy would be Fboyancy=dhelium×Vdisplacemwnt×g N.

    If thease are in equilibrium (the guy floats): Fboyancy=Fg

    dhelium×Vdisplacemwnt×g =70×g

    If dhelium is 0.178 kg/m3 then 70/0.178 = Vdisplacemwnt= 393.5 m3≈ 1.9 m3 per condom.

    Like i know condoms are super strechy (can hold about 40L air befor burating) but wow. Thats like a phone booth per condom.

    Did you need this info?.. no. Was i compelled to calculate this? … no … stay in school kids.

    • DagwoodIII@piefed.socialEnglish
      37·
      20 天前

      Classic rookie mistake.

      Not every store has an unlimited supply of condoms, especially the extra large ones*.

      He brought 200 at her store, and emptied the shelves. He probably hit a dozen places and brought all they had on hand.

      *I shall modestly refrain from enumerating the many, many times I myself have needed to purchase a vast number of extra large condoms…

    • NoneOfUrBusiness@fedia.io
      211·
      20 天前

      I’m sorry to say this, but your autism has failed you. Buoyancy is proportional not to the mass inside the displaced volume, but to the displaced mass, which is to say the difference between the mass inside the displaced volume and the mass of the medium that would’ve otherwise occupied it. In this case that means Fbuoyancy=g(dair-dhelium)Vdisplacement. The density of air is about 1.23kg/m³, so your answer six times too big.

      • ab60753@lemmy.zip
        6·
        20 天前

        Ye thanks. Jesus i cannot. What i have learned. DO NOT ATTEMPT TO DO MATHS WHEN GOING TO BED.

        Thank you

          • Zarobi@aussie.zoneEnglish
            2·
            19 天前

            For context, autism doesn’t really have anything to do with accuracy of maths. It has symptoms like difficulty communicating and special interests.

            It’s hard to explain, but “your autism has failed you” just feels weird. I have autism myself. I’ll probably struggle to explain why, but here goes:

            • The original comment was using autism as a joking explanation as to why they enjoy doing calculations. The reply turns that against them: “your autism should have made you good at this, but you failed.” It’s ok to have self deprecating humour, but it’s less funny to deprecate others.
            • It reinforces the stereotype that all autistic purple must be good at calculations, logic, and detail oriented tasks. As if it’s a superpower or special talent, and this person’s autism powers simply failed to activate correctly. It turns the joke into a standard they’re supposed to meet.
            • It makes the mistake seem more serious and personal than it is. We’re calculating condom based floatation devices here lol

            They could have just supplied the corrections to the calculations without making it about their identity. I assume (in good faith) that they meant it as a joke as well; it just came across as a bit insensitive and demeaning.

    • exasperation@lemmy.dbzer0.com
      17·
      20 天前

      Density of air is about 1.23 kg/m^3 at standard pressure/temperature at sea level.

      Density of helium is about 0.16 kg/m^3.

      That’s a delta of 1.07 kg/m^3. So for a 70kg man, they would need helium balloons equal to 65.4 m^3, or 65400 liters. Spread across 200 condoms, that’s 327 L per condom.

      I’m not sure where my numbers come up differently from yours, but that’s still not feasible.

      • CannonFodder@lemmy.world
        111·
        20 天前

        Hardly matters as the salient amount is the weight of the displaced air, not the weight of the helium or hydrogen. However using hydrogen might lead to a nice flameout.

        • wolframhydroxide@sh.itjust.works
          11·
          20 天前

          No! What matters is the comparative density, and you must calculate the total mass of the air displaced, as well as the mass of the gas being used to displace it. Hydrogen is half as dense as helium. Is it a tiny mass difference? Actually, no, it’s quite significant.

          Let us be charitable to my ability to calculate and say that the condoms are, themselves, massless (please don’t make me use more complex equations in an internet comment). Given 70kg of displaced air, and using the ISO atmospheric density of air of 1.2250kg/m^3 at 15C, and that hydrogen and helium have densities of 0.0841kg/m^3 and 0.1662kg/m^3 respectively at that temp, each cubic metre of air displaced by hydrogen reduces the effective weight of the balloon by 82 grams more than helium, meaning that, given a fixed number of condoms, they need be filled only 93% as full with hydrogen (reducing strain) or, given a fixed volume, we require only 93% as many balloons. For a 70kg person with massless balloons each containing 40L of gas, this amounts to 1642 condoms for helium, but only 1534 of Hydrogen! That’s a difference of over a hundred condoms that this guy doesnt have to buy.

          If need be, I can provide work shown for this problem.

          • CannonFodder@lemmy.world
            5·
            20 天前

            Yeah I agree with your math (well I haven’t checked it but it sounds about what I’d expect). But 7% isn’t a big amount within the other approximations going on here. The point is that it doesn’t double using helium even though the density is double because the relevant change is the difference between air and the other gas - which as you say is only 7%. Like if you could somehow make a weightless container that had a perfect vacuum in it, you’d only gain another 7%.

          • exasperation@lemmy.dbzer0.com
            2·
            19 天前

            Hydrogen is half as dense as helium. Is it a tiny mass difference? Actually, no, it’s quite significant.

            7.7% increased buoyancy per unit volume isn’t nothing, but I’m not sure it would qualify as “quite significant” in a colloquial sense.

      • wolframhydroxide@sh.itjust.works
        61·
        20 天前

        The other person who replied to you is deeply wrong. See my reply to them here for complete calculations. You can’t simply ignore the mass of the gas with which you’re replacing the air, despite their suggestion. If the mass of what’s inside the balloon doesn’t matter, you might as well fill it with lead. Hydrogen is something like 7% More efficient than helium for balloons. You have a good idea, and hydrogen balloons don’t just explode for no reason. They’re dangerous, but saying that they’re necessarily going to flameout is ridiculous