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Cake day: July 20th, 2023

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  • Ground hornets pattern match too. I had a massive nest I had never noticed in an old stump. They hadn’t bothered me despite having walked by numerous times. Then one time I hit the nest with the riding mower. Man that sucked. I’m not outright allergic, but a dozen stings does make me feel sick. After that, anytime I got within 20ft of the nest with the mower they would come out in force.

    Then a few years later I had the same thing happen with a raised garden bed. They never bothered me and I didn’t even know they were there, until my weedwacker attacked the entrance of the nest. I had to steer clear of that section of the garden for a few weeks after.

    Ground hornets are horrible.





  • Fermion@feddit.nltoScience Memes@mander.xyzBlack Holes
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    6 months ago

    Yeah, black holes in media where they are depicted as a giant space vacuum cleaner is a big pet peave of mine. Unless you get really close, nothing is remarkable about the orbital mechanics of a black hole. The equivalent mass star would have burned you up at a much further distance than the gravity starts to become noticeably wonky.

    It’s a shame that writers focus so much on the gravity and neglect accretion disks and astrophysical jets which do extend large distances and are visually stunning as well.










  • Are you familiar with the difference between polar (r, theta) coordinates and cartesian (x,y) coordinates? Parabolas are the solution to gravity that is uniform no matter where you sample. It assumes that gravity points in the same direction with the same magnitude no matter where you are. In this model, gravitational acceleration is always 9.81 m/s^2 in the -y direction. That is a reasonable simplification for things that are at the human scale constrained to near the earth’s surface. Deviations from air resistance will matter far more than errors stemming from that assumption anyway.

    Conic sections are the solutions to gravity that is between two objects where the force is along the line between the center of mass of both objects and the strength is inversely proportional to the square of separation. Now you need polar cpordinates and the direction of gravity changes as things move around. This works pretty well for orbits around the earth and orbits around the sun, because the earth is so much more massive than sattelites that orbit it, and the sun is so much more massive than things that orbit it. If you need really precise orbit trajectories, ellipses aren’t truly accurate either. You need to account for all the orbiting bodies in the system. The 3-body problem famously doesn’t have purely analytical solutions, and you need to resort to numerical methods to calculate trajectories.

    So both solutions come from simplified mathematical models. Despite being simplifications, their predictive power is actually very goood. However, like you are intuiting, it’s important to know when those simplifying assumptions lead to errors that start to become important. It’s hard to come up with a particular threshold for when you need to switch from one model to another, because it really depends on how much accuracy your application needs.