• 3 Posts
  • 403 Comments
Joined 3 years ago
cake
Cake day: January 5th, 2024

help-circle


  • Took me a while to understand what you’re warning against. Allow me to rephrase, and tell me if I got it wrong.

    The || will execute what’s after it in two cases:

    1. The preceding command (in this case the rm) never ran because of an earlier &&
    2. The preceding command ran and returned nonzero

    OP’s code relies on the 1 case, but wrongly assumed that the 2 case will never happen. That’s the footgun.


  • Illuminating read. Thanks.

    It doesn’t answer the obvious question though. The host (Bluesky/Eurosky, which apparently is called a PDS) is still effectively an instance, isn’t it? You can host your own, but you’d probably use one that’s already set up. It doesn’t seem that different from Mastodon in that sense.

    The other big question is, how does the migration work? I’ve heard that Mastodon’s migration is less than perfect. But this blogger says they’ve moved from bsky to Eurosky, and I just want to know how that works – if I have a client subscribed to that account back when it was on bsky, how will my client know where to look now?

    Edit: okay, I did a little searching, then after getting no useful results gave up and asked the big data machine that’s making everyone’s lives worse. I kinda get it now, but not enough to explain here. But it sounds like a good system.













  • That awesome… and/or horrifying. I’m so glad I’m comfortable with the default configuration my body came with, and don’t often have to think about stuff like this. But I’m also really glad you seem happy with the results of your, uhhh, renovations!

    Although… What exactly is a male socket? I’ve always thought of it as an outlet, nothing goes into it, stuff only flows out.


  • I love this. Certain surgeries absolutely involve some amount of “plumbing”, e.g. connecting the blood vessels in a pig heart transplant (I think they even refer to it as plumbing, perhaps informally). And I think it’s very accurate to say that plumbers, electricians etc. are to houses as surgeons are to living creatures.



  • So we might think: a cube falling through a floor portal and flying out another floor portal right next to it, kinda looks like how a bouncy ball bounces off the floor, and should apply forces on the floor similar to that - an elastic collision. Unfortunately, this brings us right back to conservation of momentum, which didn’t work out. But maybe I just did it wrong? Maybe, if done more carefully, conservation of momentum can work without being dependent on the reference frame?

    I genuinely don’t know yet. Time to bring out the calculus.

    We have:

    M = the mass attached to the portal (e.g. the floor)

    V = the velocity of M

    V’ = dV/dt = the acceleration of M (assuming no other forces)

    F = MV’ = the force applied on the portal

    m’ = dm/dt = the rate of mass entering the portal

    v = the velocity of the mass entering the portal

    If we assume conservation of momentum (our old nemesis), the force applied on the portal should be the same as the momentum taken from the mass entering the portal:

    F = m’v

    But now we’re back to the case from before, where the choice of reference frame changes the outcome! We’re not having that. So I hereby decree:

    The force applied upon a portal by a mass entering it must be calculated by conservation of momentum in the intertial reference frame of the portal itself at the instant under examination.

    This gives us, effectively: F = m’(v-V)

    Now THAT’S something we can work with!

    Note that this formula also works for the exit portal. In that case, m’ is negative.

    A curious result follows.

    For the entry portal, m’ is positive, and (v-V) is a vector pointing into the portal. (This must be the case, otherwise the mass would be exiting the portal). Therefore, the force would be pushing the portal into the wall.

    For the exit portal, m’ is negative, and (v-V) points out of the portal, therefore the portal again would be pushed into the wall.

    The result: whenever anything passes through a portal, both ends always get pushed in the same direction.

    So, back to my thought experiment.

    If a portal attached to a free-falling panel falls onto a cube, the cube’s entry into it would brake its fall to some extent. However, this wouldn’t be the only force in play.

    As I said in my previous comment, forces applied between the two halves of an object going through a portal, get applied to the portal itself. In practice, this mostly means tension and compression forces. In the static analysis from before, it was compression.

    As the panel is falling onto the cube, a part of the cube is already out the other side and moving away the portal. If the panel has slowed, this would apply a pulling force (tension) on the part of the cube that still hasn’t made it in. This tension force actually compels the portal, and the panel it’s attached to, to speed up towards the ground.

    So, in total, would the panel be slowed, accelerated, or unaffected? Maybe the forces cancel out and it just continues on its normal freefall? I don’t know yet. Would need to do more math.


  • Okay, after thinking about this a while, I’ve decided that conservation of momentum just doesn’t work, unless the portal actually absorbs the mass of every object passing through it, which would probably cause its own set of contradictions.

    Instead, I think forces that act through the portal are applied to the portal. What do I mean by this? Well, take this classic case of a cube floating halfway through two floor portals:

          ____            ____
         |    |          |    |
    ___++++++++++______----------___
    

    (sorry, can’t do better than ASCII art right now)

    The system has reached equilibrium, and nothing is moving. Both halves of the cube are being pulled down by gravity, but cancel each other out by applying a normal force on each other right at the portal interface. What I’m claiming is that this normal force is applied to the portals, which ultimately transfer it to the floor. If this entire floor was a scale, it would measure the calibrated weight of the Weighted Storage Cube.

    But this is the static analysis. What happens when objects are in motion? To be continued…