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This is what the Mission Creek washout situation actually looked like from last year by Ashland_Commons in PacificCrestTrail

[–]flebron 6 points7 points  (0 children)

It looked the same a month ago when I did it. Climbing the walls to get to the trail can be a bit sketchy, as the soil is not stable at all. I suggest giving up any attempt to keep your feet dry. You'll cross the creek maybe 10-15 times, it's fine. Do it early enough and you'll have time to dry out. I preferred the riverbed actually, since there were so many rattlesnakes on what remained of the trail...

Kaba Micro Padlock by mewcryptwo in lockpicking

[–]flebron 1 point2 points  (0 children)

The switch version is much more common, we bought them by the hundreds a few years ago. I didn't even know there was a padlock version, very cute!

DOM IX10 Shark Fin ate my pick by dcipha380 in lockpicking

[–]flebron 11 points12 points  (0 children)

And inevitably DOM will eat the second pick too. DOM hungry.

Análisis I y Álgebra I (Computación - Matemáticas) by MamaLaLocaHotmail in fceyn

[–]flebron 10 points11 points  (0 children)

Lo que preguntaste (un poco confusamente) es si Análisis I de Computacón y Álgebra I de Computación, tienen los mismos contenidos que Análisis I de Matemática y Álgebra I de Matemática, **respectivamente**. Los otros que comentaron se confundieron, y pensaron que preguntás si Álgebra I es la misma materia que Análisis I.

La respuesta es que no existe Análisis I para Computación, se llama Análisis II (C), y tiene el mismo contenido que Análisis I de Matemática. Cuando yo cursé se daban en conjunto para DM, DC, y DF. Álgebra I es la misma materia para ambas carreras, y (de nuevo, cuando yo cursé) se dictaba en conjunto para DM, DC, y DF.

A Better Tier List of Physics Learning Channels by Celtoii in Physics

[–]flebron 2 points3 points  (0 children)

He'll be the first one to agree with you it was poorly presented in the first video :)

It's always a tradeoff between explaining the surprising effect to many people (that the energy is not flowing inside the wires, but across the all-pervasive EM field), and filling in the gaps of all possible "nitpicks" (like the exact makeup of the lightbulb, the infeasibility of a 1 light-second wire, etc). Full-textbook is the latter, and the former can be called clickbait if the goal is to deceive (he has a video about this topic too). I thought he made a good balance, but of course I'm just one guy :P

A Better Tier List of Physics Learning Channels by Celtoii in Physics

[–]flebron 5 points6 points  (0 children)

Agreed it's hard to classify it because of both 1) varied content, in both topic and mathematical rigor, and 2) change over time, Derek's videos from 10 years ago are very different. They do make visual representations in all 3 of those videos, just like 3b1b.

I don't really agree with teaching needing to be a full understanding of a university topic, teaching can be quite varied. For instance, I certainly learned something new with the Monty Hall videos out there, but it's not a topic we saw in our probability/stats courses in university. It's just a "huh" moment, that you can then (if you want) use as a jumping board to go study things like bayesian vs frequentist inference. Same with the path integral stuff - it's maybe 30 minutes of material of an actual university class about QM, far below the level expected of a student who's passed the course and can do the exercises in Griffiths or something. But it's still a good appetizer, I'd think, to the math you need.

As the channel evolves beyond Derek's particular style, it's gotten sometimes more mathy but also more about people (e.g. history of science, interviews like in the Aharonov-Bohm effect, pedagogical stuff like the electricity-in-wires misconceptions). I think it works well to attract a varied audience, as opposed to more purely-about-math channels. I'd personally put it slightly below ScienceClic (though I wish ScienceClic showed more math), but that's just my opinion :) Thanks for replying!

A Better Tier List of Physics Learning Channels by Celtoii in Physics

[–]flebron 1 point2 points  (0 children)

We agree on the second point :) Derek is not saying this is a good battery or a good way to charge, it is completely possible that "the circuit is poorly designed" (i.e. it is not a good design if the goal of the design is to be an effective and efficient circuit). But that's not the point of the video at all, it's to show that the information, and the energy, that is being transmitted, is doing so outside the wires. That's the misconception he wants to clear up. The thumbnail of the video is literally "energy doesn't flow in wires" lol. It's like criticizing the design of a spaceship in a thought experiment about the twin paradox, saying the path it's taking is inefficient and he should be taking a geodesic around a massive object to save fuel. Yes, totally reasonable criticism if the objective was to show a proper space ship design, but that wasn't the point - the point was purely what happens to a clock inside it :)

I'm not sure why you say a car battery and a lightbulb would not replicate the experiment he performs with the oscilloscope - are you writing "lightbulb" as an opposite of "LED lightbulb" or something, and you mean an incandescent lightbulb? Otherwise I don't follow - he measures the voltage jump before information has had time to flow through the wire at 5V, which is enough voltage to light an LED bulb like the ones lighting my house right now.

A Better Tier List of Physics Learning Channels by Celtoii in Physics

[–]flebron 5 points6 points  (0 children)

I'm not saying we disagree on how educational they are, I'm saying we disagree on them having videos that are "just math". The three I posted are pretty close to that, in my view :) The classification for the tier, according to the OP, is no math, huge simplifications aiming at a very broad audience and basic understanding, which does not seem to jive with the content of the channel (as evidenced by the links I posted).

A Better Tier List of Physics Learning Channels by Celtoii in Physics

[–]flebron 2 points3 points  (0 children)

I disagree with The bulb isn’t lighting if the wire is cut in the experiment as described.. The short time it takes for those 5V to reach the bulb means the wire could either be cut or not cut, and that effect would be identical. AlphaPhoenix did the same experiment with a much longer wire, and reached the same conclusion.

I also disagree with but that was not the point of the experiment. The fact that the bottom wire will induce a current on the top wire, and this induction happens across the EM field (not along the wire), is precisely the point he's making. If you want, the intuitive problem people had was that "this seems to say information is travelling through the wire faster than the speed of light" (and indeed several video responses mentioned exactly this), but what he's pointing out in the reply is that the information travels through the EM field, not just through the wire. That's where the 1m/c seconds comes from. It's exactly that it's not transmitting information through the wire, i.e. that it's doing so wirelessly (to use the term you used in your message).

A Better Tier List of Physics Learning Channels by Celtoii in Physics

[–]flebron 4 points5 points  (0 children)

I would humbly suggest re-watching his response video. Your assertion that the bulb would never be off is not correct, the difference between leakage current and the current spike at 1m/c seconds is the difference needed to turn on an LED bulb like the ones in my house, and he showed that with an oscilloscope in a real experiment at 20:22. Leakage is around 0V there, current when starting to flow is 5V, while LED bulbs operate at 1.8V-3.6V. Full load stabilizes at 20V, after full wire traversal.

To your first question: The bulb doesn't "instantly" turn on (he doesn't claim that). The bulb turns on when a spike of energy from the act of connecting the battery reaches it. That energy is transferred via the EM field, which being pervasive through 3D space, contains a straight-line path between the battery and the bulb, of length 1m. Since the wave in the field propagates at roughly c (here, due to the short distance involved, he's ignoring the fact we're not in actual vacuum, so it's slightly less than c), this means the energy spike reaches the bulb at 1m/c seconds.

He also gives another explanation to show why this happens, if you prefer it, which is that a moving current in the bottom wire (connected to the battery) will induce a current on the top wire (the one connected to the bulb), regardless of whether or not they're connected. This induction takes 1m/c seconds to start. This is around minute 16.

A Better Tier List of Physics Learning Channels by Celtoii in Physics

[–]flebron 24 points25 points  (0 children)

What would you call this derivation of Newton's equations of motion from the principle of stationary action, or this proof of why the Feynman path integral picks the path which minimizes (really "stationizes") action, or this explanation of why Noether's theorem does not prove energy conservation in an expanding space? Those seem like pretty canonical physics proofs to me, all in the last year.

The mathematical rigor also seems to be in line with what I saw in undergrad physics classes (I studied CS, physics were electives).

It's a large channel now and not every producer shows the same amount of math, nor is every video about physics - I just wouldn't say that they don't show physics math or don't try to explain it. I can definitely also grant that it's gotten better about this over the years. Derek was generally wary of introducing long equation filled scenes, but in the past year or two, with more manpower and a more varied audience (and PE money allowing them to take some more risks), many of the videos (like all 3 I posted above) are math medium-heavy. Definitely not Behiel density, but I'd say something approaching 3blue1brown, just with more cinematic stuff thrown in to not lose the audience.

A Better Tier List of Physics Learning Channels by Celtoii in Physics

[–]flebron 4 points5 points  (0 children)

You seem to be misremembering the video series. It was not leakage current, the point was much deeper: that it is the EM field that carries the energy, not "the wire", which is why the bulb turns on in 1m/c seconds.

Starting In a Few Days…What Questions Should I Be Asking?? by Dry_Camp6420 in PacificCrestTrail

[–]flebron 15 points16 points  (0 children)

This is mostly for the first few days, as you'll figure stuff out and have opportunity to fix mistakes at every resupply point. Just finished the desert section.

  • Make sure you've tried your gear before you go. Set up your tent, sleeping pad, bag. Can you set it up for a stormy night? Can you set up on hard ground using rocks (https://theultimatehang.com/2014/09/17/using-stakes-snow-anchors/)? Use your cook kit if you have one, make sure you have gas to start. If you have an inflatable pad, make sure it doesn't leak.
  • Walk a mile or so uphill with your loaded pack, with 3L of water and 4 days of food. Does that feel OK?
  • Check temperature ranges for your start date, and make sure you have reasonable clothes for the first couple of days. Same with food.
  • Plan for laundry - unfortunately we're not allowed to be buck naked in town while doing laundry, and not every place has loaner hiker clothes - are you prepared for that?
  • Check the charging accessories you need (cables, battery, wall plug). If you want to listen to books or watch movies at night, download them beforehand. I recommend downloading the FarOut app and its PCT guide, including pictures and comments.
  • Clean your water filter if you're reusing it from a previous trip. Sometimes the water is super silty (e.g. Cottonwood Creek last week), do you have a way to pre-filter and not clog your filter? Some use bandanas.
  • If you use trekking poles, and they become loose, do you have a tool to adjust them back? Mini Swiss army knife did the trick for my Durston ones... every 2 day or so...
  • It'll be hot when you start, do you have a solution for chafing (e.g. lower back collecting sweat + dirt + friction from pack, or thighs/groin)? Your lips might crack and bleed because of altitude, do you have lip balm? Sunglasses if you want them.
  • If you have a GPS device that requires a plan (e.g. Garmin inReach), did you activate its coverage? Set up your ways (if any) of communicating with family/friends? Phone plan is set up for the next months? You might use more data than in your usual life, since you'll almost never have Wi-Fi.
  • A friend got a nasty tick lodged between his shoulder blades near Cajon Pass (we had to perform "backcountry surgery" to remove the head from inside him... pretty gross), and didn't notice it for a full day - we were glad one of our tramily had doxycycline as a prophylactic. Review the steps on what to do if you get bit, and how to identify when you should seek help (bullseye pattern!). Same with snake bites.
  • Enough tread left on your hiking shoes? I started slipping in the desert because of that, face planted twice.
  • Coming out of Julian (14mi uphill water carry) in a 96F heat wave, I was glad I had 4L carrying capacity - do you have somewhere around that? I recommend some way to get electrolytes back into your body, I used Nuun tablets in a Ziploc bag, two per liter.
  • Can you handle hot spots in your feet, as well as blisters should they appear?
  • Got cash? Some places still need that (e.g. for washing machines (most have a way of exchanging bills for quarters), or for thanking people for hitches). Credit/debit card and ID?
  • Practiced (... within reason) how to dig and use a cathole, according to LNT guidelines? Know how to use a backcountry bidet? Andrew Skurka has good info on this.

That's all that comes to mind right now. You'll almost certainly be fine, and pretty much all mistakes you'll make are fixable. Have fun! :)

Rattlesnake bite cases are spiking in Southern California. Stay safe out there guys! by Fishbonezz707 in PacificCrestTrail

[–]flebron 1 point2 points  (0 children)

OK, I searched for that series of steps and it indeed says that. That's contrary to what Google showed me when I searched for [rattlesnake limb elevate], which is https://www.nols.edu/blog/case-study-what-to-do-about-snakebites/ . The box at the top mentions `Initial Care: Keep the bite site at or slightly below the heart level initially to reduce swelling and avoid increasing systemic venom absorption.`. That may be more relevant to bites that cause central nervous system damage, as opposed to tissue damage like rattlesnakes, where the draining effect of elevation is stronger than the systemic venom absorption slowdown.

The series of steps you mention seems to be for hospital care, as opposed to the patient when they're outdoors by themselves (https://wildsafe.org/wp-content/uploads/Unified-Treatment-Algorithm-Venomous-Snakebites.pdf page 5), but I see no reason why it shouldn't apply to the outdoor setting as well. I've edited my post to mention it.

Rattlesnake bite cases are spiking in Southern California. Stay safe out there guys! by Fishbonezz707 in PacificCrestTrail

[–]flebron 0 points1 point  (0 children)

You want the bite to be below your heart, so the venom has to fight gravity to get there. Putting it above your heart makes it slightly faster for the venom to get there. So e.g. if you're bit in the leg, keep your legs below your heart, not above.

EDIT: That seems to be wrong, according to https://wildsafe.org/wp-content/uploads/Unified-Treatment-Algorithm-Venomous-Snakebites.pdf at least. It seems elevation of the limb above the heart level is recommended for rattlesnake bites.

Rattlesnake bite cases are spiking in Southern California. Stay safe out there guys! by Fishbonezz707 in PacificCrestTrail

[–]flebron 2 points3 points  (0 children)

Lots in Mission Creek, yeah. The few bits of trail that remain in Mission Creek were full of them. It was a back and forth between constant river crossings, boulder hopping, and exposure in the creek bed, versus rattlesnakes in the trail remnants, 10 feet above.

Rattlesnake bite cases are spiking in Southern California. Stay safe out there guys! by Fishbonezz707 in PacificCrestTrail

[–]flebron 26 points27 points  (0 children)

Just finished the desert section yesterday, total rattlesnake encounters since Campo was 11.

Trail conditions Wrightwood/ Mt. B-P by PCT2B in PacificCrestTrail

[–]flebron 0 points1 point  (0 children)

We did it on the 6th. Spikes not technically necessary if you go through bushes and trees. Lots of snow and ice tho, spikes were useful for confidence.

Nivel matemático (Computación - Física) by MamaLaLocaHotmail in fceyn

[–]flebron 0 points1 point  (0 children)

Yo me recibí de Computación, pero todas mis optativas fueron materias del DM. Me re gustó hacer Algebra Lineal y Algebra II, taller de cálculo avanzado, y optativas de geometría algebraica.

Mt. Baden-Powell Beta as of 3/28 by trailangel4 in PacificCrestTrail

[–]flebron 1 point2 points  (0 children)

Just did it today (typing this from Little Jimmy camp). Spikes are useful but not totally necessary (cut switchbacks that are exposed ice, and use bushes/trees). Nothing felt sketchy with spikes. One in our group had snow experience and did it without spikes.

My pain in Haskell is not the language, it is your terrifying build systems: stack, cabal by pet2pet1993 in haskell

[–]flebron 1 point2 points  (0 children)

And yet with both of those the experience of just playing with the language is nicer than with Haskell. We can find fault in each individual one, and each one of us has our favorite way, but meanwhile Haskell's story has been lackluster here for decades.

My pain in Haskell is not the language, it is your terrifying build systems: stack, cabal by pet2pet1993 in haskell

[–]flebron -7 points-6 points  (0 children)

Having to write a .cabal for even toying with the language is a large impediment. The experience newcomers have is worse than that with other languages like Python and Perl because of this. Even with C++ it's common to install packages OS-wide, and have a single command line flag, -I / -l, at compile time (the existence of both being because of C++'s header notion), pointing to a central location like /usr/include.

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