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Cake day: July 1st, 2023

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  • At the risk of feeding the troll, here is the math you are suggesting we do, which disproves all of your arguments. It pains me how confidently you speak of a topic you are clearly so uneducated about: your physics mentors should be disappointed in you.

    Conservation of linear momentum:

    m1v1i + m2v2i = m1v1f + m2v2f

    Let the vehicle be m1 and the human m2. Let the human’s initial velocity be zero. Let us further assume an inelastic collision: the human and vehicle end up at the same final speed v1f=v2f=vf.

    Thus:

    m1v1i = (m1+m2)vf

    What we are concerned of is the ratio of initial vehicle speed, v1i, to post-collision speed vf. Your argument is that a lighter vehicle will have a larger drop-off in speed, recovering energy and reducing the severity of the collision. If you were right, the ratio v1i/vf should be less than 1.0, and be significantly different for a heavy and light vehicle. We will prove this wrong shortly.

    Rearranging:

    v1i/vf = m1/(m1+m2)

    Already it is abundantly clear that when m1 >> m2, v1i/vf will be 100%. I will leave you no room for counterargument here by working two examples. Take the most popular pickup truck, the Ford F150, at 2125 kg. Take one of the smallest compact cars, a Honda Fit, at 1130 kg. Take the average adult human, at 65 kg.

    For the F150: v1i/vf = 2125/(2125+65) = 97%

    For the Honda fit: v1i/vf = 1130/(1130+65) = 95%

    At 35 mph, that’s a difference in speed delta of 0.7 mph, which is absolutely insufficient to explain the delta in injury severity presented in this article.

    This proves what everyone knew all along: vehicle mass is insignificant in crash severity with a pedestrian because the masses of the two objects are so different. When the masses are similar (e.g. a small car colliding with a big car) yes, mass is important. But that’s not what is being discussed and is not your argument.

    I hope you go back to school and learn the basics before confidently acting superior. Take your downvotes and learn from this to do better.





  • Two facts:

    1. The average occupancy of a car in my North American city is 1.2 people per car. This does not vary much by city.
    2. Autonomous vehicles will almost certainly be worse for traffic than human driven cars. They will circle empty with no passengers and drive to pick up passengers empty (dead heading) even with a fully rideshare system. If there is widespread private ownership of autonomous vehicles (and you bet your butt that car companies will campaign for this aggressively to keep sales up), the dead heading problems only multiply. If you don’t believe me, look up any recent literature on the topic: by most accounts it will be worse, not better. Dead heading is only the tip of the iceberg of problems there.





  • I as pro-EV as the best of them. A cradle to grave emissions drop of 40% is a great step forward on reducing transport emissions (public transport and active transportation are a whole other aspect of this we’ll avoid here). However, characterizing the energy gap for EV charging as a non-issue is disingenuous.

    You’ve correctly pointed out that peak hours are when the grid is most strained and vulnerable. Well, if most everyone who drives to work starts charging their EV when they get home from work, that is at the highest peak of the day: around 5-7pm. It’s the addition to the peak curve that’s the real concern. In most places, that means triggering on fossil fuel burning facilities to meet that peak demand. It also means increased peak loads on the transmission infrastructure that could overwhelm it.

    That being said, there are some simple solutions: e.g. charge EVs on off-peak hours, smoothing out the demand on the grid. Where I live there is already an incentive to charge overnight in the form of ultra low overnight rates. I’m sure we’ll find the solutions, but please don’t pretend it’s not a problem.









  • As with most sci-fi the author gets loopier in the later books. That being said:

    • Dune: masterpiece of philosophy, one of the best books ever put to print
    • Dune Messiah: a worthy sequel and must read after the first book; completes Paul’s arc
    • Children of Dune: more plot driven than the first, but still thematically rich and entertaining.
    • God Emperor of Dune: the most divisive of the books: you love it or you hate it. I am in the love it camp, the book is unhinged and the themes are marvelous. This is where I’d stop a read of the series.
    • Chapterhouse and the other (Heretics?): forgettable in my opinion, simply because I’ve forgotten them. Later book fan opinions welcome.
    • anything Brian Herbert: not terrible but not awfully good either. Makes for decent light reading I guess, and there’s good lore building in some of the books despite some unforgivable retcons (Agemmemnon, sigh)

  • yimby@lemmy.catoCrossView@lemmy.worldEarthrise
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    11 months ago

    I have definitely had this experience in KSP and never really thought about until this comment. Neat!

    However, there is a practical reason the Apollo mission orbited on its side like this. The side of the spacecraft facing the sun would get very hot while the side facing away would get very cold. So the spacecraft would roll slowly as it travelled for passive thermal control. They literally callrd it the barbecue roll.

    Orbiting a planet along it’s equator means orienting north/south (normal/antinormal) for a natural roll axis. Neat stuff!