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Cake day: June 13th, 2024

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  • isaacd@lemmy.worldtoxkcd@lemmy.worldxkcd #3090: Sail Physics
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    2 months ago

    Yes, it’s possible (and common) for a boat to sail against the wind by the power of its sail alone. Sailors have known this for hundreds of years but if it sounds impossible, no worries, I thought so too at first.

    Here’s how it works, simplified so I can get in trouble with pedants:

    The boat, first of all, has a keel (the blade-like bottom of the hull) which “locks” it into movement along a single axis: forward and backward. The wind is not going to blow the boat sideways, at least not very effectively.

    Second, sails are curved, not flat, and can rotate (when seen from above). The force created when the wind deflects off the sail matches the curve of the sail, more or less.

    So if the wind is blowing directly south ⬇️ and you want to travel north ⬆️ you angle the boat northeast ↗️ so it can only move northeast or southwest. Then you point the sail east ➡️ so the wind gets deflected west ↩️. Newton’s third law does the rest. When the wind hits, the boat will move northeast ↗️ because the keel prevents it from going straight east.

    Then after a while you turn the boat (“tack”) northwest ↖️, point the sail west ⬅️, and continue.


  • There’s a handful of us that do 50 for FOSS: https://50forFOSS.org

    tl;dr: on the first Friday of the month we each pick a FOSS (free/open-source) project and give the maintainer $50.

    Thanks and encouragement is great too. As a small-time open source maintainer, it seems awareness has been spreading over the last few years and people are going out of their way to be kind and respectful when they raise issues; it really makes a difference. But financial sustainability and community ownership are separate and arguably more essential issues if we want FOSS to survive over the long term.

    I did have one maintainer turn down the $50 and ask me to donate it to UNICEF. It’s all the same to me as long as it makes the work more sustainable for them.



  • Kavita for my ebook collection—mostly tabletop RPGs, but some comics and sci fi as well.

    I don’t actually use the web interface that often. I add books to my Kavita library, then scan the OPDS feed into my scratch-my-own-itch mobile app, Bookoscope, and download whatever I want to read onto my tablet from there.

    Side note, PDFs are the absolute worst. Even reading them on a full-sized tablet is incredibly annoying. Anybody have any tips/tricks/apps for that?