I got stuck on my physics homework because I was cocky enough to think I didn't have to read the text for this chapter. made the same mistake for the last chapter. So I start taking notes for this chapter, get distracted by my profs website and start reading papers he worked on (some of them were about novae and nuclear astrophysics and were interesting, what little I understood). Then I ended up trying to understand what I couldn't figure out in his papers.
IN this way I burnt an hour I should have spent studying and doing work, so now I'm going to take notes on the section for the lecture tomorrow and take a failing grade on the last half of the HW. I can do the HW later and understand the concepts, but I'd rather work on getting caught up and stop falling behind since I procrastinate. Also, one failing grade on half of one of 8 hw assignments worth 8% of my total grade is not going to affect my grade.
I take it you mean all of the homework combined is worth 8%? Because 4% of your grade would be pretty substantial.
[QUOTE=Falubii;46243951]I take it you mean all of the homework combined is worth 8%? Because 4% of your grade would be pretty substantial.[/QUOTE]
yes, all of it combined is 8%. I already took notes on what I messed up on yesterday and did what I didn't turn in, it was actually quite easy.
[QUOTE=paindoc;46245216]yes, all of it combined is 8%. I already took notes on what I messed up on yesterday and did what I didn't turn in, it was actually quite easy.[/QUOTE]
That's surprisingly low for a physics class. I guess I haven't taken that many yet, but they always seem to put homework around 30-40% of your final grade.
[QUOTE=Falubii;46245925]That's surprisingly low for a physics class. I guess I haven't taken that many yet, but they always seem to put homework around 30-40% of your final grade.[/QUOTE]
Yeah, its graded kinda funny. Midterms are 37% of our grade, and those are best 2 of 3. Final is 28%, labs are 11%, tutorial is 8% and HW is 8% as well. Also there are conceptual questions answered in class that are full-effort full-credit that are 8% as well
So I've been going through some older posts in this thread but if I'm reading it right, the famed and worshiped JohnnyMo was not a prodigy when he first started physics? Because I got a shit grade on my first exam (72 on MC, 52 on first short response, 45 on second short response). I'm well within standard deviation overall, since the average is 73 and st dev is 17% but I really felt I did better than that. I was pretty devastated at first, but had to remind myself I didn't study as hard as I could have and that I'm in an honors program at one of the top 20 universities in the country.
I don't know what this rambling is for, but I have a real passion for the physics of space and its application to spacecraft, and I'm feeling like I made the wrong choice of major (Aero and Astro Engineering) if physics is this unintuitive. I'm trying to be better though, I've started taking notes out of the book (rephrasing what he writes) on the subject of the lecture the next day, and trying to do the example problems. I'm also trying harder with in-class notes and attention.
So did all you more intelligent motherfuckers have difficulties like this where you felt like quitting or am I just in the wrong program?
[editline]20th October 2014[/editline]
oh also we apparently had a nuclear reactor on campus ages ago, we have a physics lab below my dorm that has a van de graaf accelerator staffed by undergrads and graduate students, and our lecture hall has a really neat foucault pendulum in the center of the spiral brick stairs to other floors
Physics is hard for everybody. Don't beat yourself up over test grades. Hard work and perseverance is more important than "intelligence."
Yeah, physics is pretty tough imho
And getting better at it requires practice. I think it's similar to how people assume that someone good at music is purely talented/some sort of prodigy, instead of being aware that most musicians practised for years.
[QUOTE=Number-41;46286694]Yeah, physics is pretty tough imho
And getting better at it requires practice. I think it's similar to how people assume that someone good at music is purely talented/some sort of prodigy, instead of being aware that most musicians practised for years.[/QUOTE]
[QUOTE=Falubii;46286420]Physics is hard for everybody. Don't beat yourself up over test grades. Hard work and perseverance is more important than "intelligence."[/QUOTE]
Thanks. I was just feeling really demoralized since I studied pretty damn hard (read book, did examples, went to office hours) and still missed points. Looking at the exam now, I missed 10 points due to lack of understanding and about 30 due to going to fast and not breaking the problems down.
And you're right, physics does seem to totally have the "musician" effect where its easy to assume someone is a prodigy. I assume at some point my friends lack of work outside of class (he hasn't even taken any notes or cracked open a book) will catch up to him. For now, I'll focus on redoubling my efforts and doing more example problems. I'm quite excited to start quantum in the spring, the professor and our excellent textbook have made me actually [I]enjoy[/I] physics for the first time. We get to solve some seriously fun (and difficult!) problems! I've never had fun with mechanics before so this is new to me. Even though my degree is applied physics essentially, I want to learn the base of theoretical physics so I can expand more outside of my degree (and do better in the more hardcore aero and astro classes involving fusion plasmas and propulsion).
Anyways, thanks again for tolerating my rant and giving me your sage words of wisdom. Last question for a while, I promise. Has anyone used the companion questions to the Feynman lectures? Looking for more practice.
[editline]20th October 2014[/editline]
oh we also got to watch water in a vacuum today which was pretty neat, but the amount of times Professor Garcia had to explain vapor pressure was just stupidly high. Seemed to be mostly kids asking theoretical questions to verify their own intelligence, with only a few asking meaningful questions. Then there was the one kid who openly said what the prof taught was a bad way of saying it (his way wasn't much better) in just the cockiest and most irritating way possible.
quite a few people ask stellar questions but some people christ
[QUOTE=paindoc;46287097] Has anyone used the companion questions to the Feynman lectures? Looking for more practice.
[/QUOTE]
I actually purchased them a few weeks ago but haven't bothered to do any yet.
So I did a bit of research after finishing my physics homework and turns out my Uni has some serious fusion credibility, and the A&A department even more so! [URL="https://www.aa.washington.edu/faculty/jarboe/"]This guy[/URL] teaches plasma and fusion physics at my Uni, and that [URL="http://www.washington.edu/news/2014/10/08/uw-fusion-reactor-concept-could-be-cheaper-than-coal/"]this[/URL] is something he is working on quite closely.
So here's really hoping I get in to my major department and am not completely behind on the curve my junior year when I get to start doing the really fun stuff. I may have to go for early admit at this point though which is REALLY damn difficult
[QUOTE=paindoc;46283362]So I've been going through some older posts in this thread but if I'm reading it right, the famed and worshiped JohnnyMo was not a prodigy when he first started physics? Because I got a shit grade on my first exam (72 on MC, 52 on first short response, 45 on second short response). I'm well within standard deviation overall, since the average is 73 and st dev is 17% but I really felt I did better than that. I was pretty devastated at first, but had to remind myself I didn't study as hard as I could have and that I'm in an honors program at one of the top 20 universities in the country.
I don't know what this rambling is for, but I have a real passion for the physics of space and its application to spacecraft, and I'm feeling like I made the wrong choice of major (Aero and Astro Engineering) if physics is this unintuitive. I'm trying to be better though, I've started taking notes out of the book (rephrasing what he writes) on the subject of the lecture the next day, and trying to do the example problems. I'm also trying harder with in-class notes and attention.
So did all you more intelligent motherfuckers have difficulties like this where you felt like quitting or am I just in the wrong program?
[editline]20th October 2014[/editline]
oh also we apparently had a nuclear reactor on campus ages ago, we have a physics lab below my dorm that has a van de graaf accelerator staffed by undergrads and graduate students, and our lecture hall has a really neat foucault pendulum in the center of the spiral brick stairs to other floors[/QUOTE]
Haha, I wish I was a prodigy now. I'd be way less worried about my grad school applications.
Falubii and Number-41 are right. Physics is fuckin' hard. It way harder than math is to me.
[QUOTE=paindoc;46287097]And you're right, physics does seem to totally have the "musician" effect where its easy to assume someone is a prodigy.[/QUOTE]
[url]https://en.wikipedia.org/wiki/Impostor_syndrome[/url]
This is pretty rampant in physics and math. It seems like everyone has the thought, "I shouldn't be here, I'm not good enough at this," at some point. And your grade wasn't even that bad. I have absolutely bombed exams in embarrassing ways (think <20%) and still passed the class. Obviously that shouldn't be the goal, but in the words of Walter Sobchak, "Nothing is fucked here, Dude."
[editline]22nd October 2014[/editline]
In other news, I was reading [I]Geometry, Topology, and Physics[/I] by Nakahara. He starts with a chapter on quantum mechanics. He starts with the postulates and talks about the Schrodinger and Heisenberg pictures and the propagator before ever bringing up the Schrodinger equation. Then he derives the Schrodinger equation from the propagator. It's so simple and cool I have no idea why my quantum course never derived it.
All you have to do is say that Heisenberg states don't change with time, and the Schrodinger state is the Heisenberg state acted on by the propagator (or whatever you call the unitary time-evolution operator), then take the time derivative:
[IMG]http://i59.tinypic.com/2rhw9js.png[/IMG]
Fuckin' elegant.
Angular momentum and conservation of angular momentum are like the most un-intuitive shit of all time and I have to know it thoroughly before monday
been doing tons of notetaking and video watching and problems but still blech
I think im posting in this thread too much buuuut I keep getting to do some neat problems in my physics book, they're pretty great. One had us finding the amount of fuel required to spin up a 3km diameter by 5km diameter long O'Neill cylinder (asteroid hollowed out as a habitat) to create 0.5gs of force on the interior surface.
It was a difficult problem, but one of few angular momentum problems that didn't suck to do! If I keep getting problems like this I may actually have [I]fun[/I] overall in the class *gasp*
:v:
[QUOTE=JohnnyMo1;46305925]Falubii and Number-41 are right. Physics is fuckin' hard. It way harder than math is to me.
[/QUOTE]
A few of my professors have made the point to me, "if it were easy we wouldn't do it," and they're entirely right.
As a physicist you're probably going to spend 99% of your career banging your head against the wall feeling stupid for the 1% of times when you have the epiphany and all of a sudden it all makes sense. Curiosity is the driving force; being a prodigy would help, of course, but when it really comes down to it the best physicists have always been the ones who have been endlessly curious and have put consistent effort in to work the problems out.
[editline]29th October 2014[/editline]
[QUOTE=paindoc;46346784]Angular momentum and conservation of angular momentum are like the most un-intuitive shit of all time and I have to know it thoroughly before monday
been doing tons of notetaking and video watching and problems but still blech[/QUOTE]
What's so unintutive about it? The total spinniness of all of the stuff in the universe must be conserved (and is probably zero). That makes sense, no?
[QUOTE=JohnnyMo1;45866789]My physics department loved Fortran. Is there some reason physicists seem to love it so much? I don't know much about coding, I ain't no nerd.[/QUOTE]
i thought that died like decades ago, is it just because physics has legacy software or something, i was at a used book store a while ago and they had volumes of code books from the early 80s on it
also my dad learned it in college
[editline]1st November 2014[/editline]
my transport homework has me using newtonian fluid equations and mass conservation equations to find the torque on a spinning thingy by the momentum imparted by a fluid flow.
so after doing all of the problems in every chapter the hw problems do not seem difficult in the slightest now. I was stuck on one for like 2 hours but when I just did it now I banged it out in easily 10 minutes.
Should have been doing this from the start, but now I'll hopefully get better than a 65 on my midterm tomorrow
If any of you have paid attention to the NaNoWriMo thread you'll know I'm writing a sci-fi story. The primary means of space propulsion in the story is nuclear fusion. Basically you have the fusion reactor and it has a hole in one side whose diameter is controlled with a magnetic field. The pressure inside the reactor causes a stream of superheated helium to shoot out the back of the ship to propel it. In theory this should provide a ridiculously high specific impulse in the 250ks range. It doesn't provide an amazing level of thrust but if you want you can also inject extra fuel into the plasma stream as a reaction mass increasing your thrust considerably.
In my story they've figured out fusion power and can get the reactors small enough to power craft slight smaller than a space shuttle. These small craft are use to ferry people from the surface to orbiting ships among other uses. However, these fusion reactors don't provide enough thrust to reach orbit; you're basically accelerating downwards due to gravity faster than you can accelerate into orbit (I know that's an awful analogy).
Rather than waste fuel as reaction mass I was thinking the craft could suck in air at the front, mix and heat it using the plasma exhaust before shooting it out the back. The moment of the plasma should push air out of the engine.
I know the diagram is awful but it should get the idea across. I've only had one semester of fluid dynamics but I'm pretty sure this would work in real life.
[img]http://i.imgur.com/mXRSsga.png[/img]
My question is what this effect is called. It's pretty similar to the bladeless fan where a small high velocity flow 'drags' a large amount of fluid.
I'd liken it more to water injection in old cold-war era turbojets. Inefficient and noisy.
[QUOTE=paindoc;46404029]I'd liken it more to water injection in old cold-war era turbojets. Inefficient and noisy.[/QUOTE]
Except water injection isn't supposed to add velocity to an airflow.
[editline]4th November 2014[/editline]
Maybe I should explain further. The blue is a airflow going around the speed of the aircraft, the red is a hypersonic (try 200km/s) high temperature plasma airflow, and the orange is a high temperature airflow heated and pushed out the engine by the plasma.
Holy fuck, calculating path integral propagators with the time-slicing method is horrible. Gaussian after gaussian after gaussian, and the expression gets worse in every single iteration. :v:
It's pretty neat though, I'm getting the financial version of path integrals, instead of the QM formulation (well, I guess it's not neat for you QM folks).
Still have no idea where I'm going with my degree, I feel like I want to apply it in an unusual way, i.e. not go into plain "nature research" but for example financial stuff, or computational stuff, I dunno...
So on my most recent physics test there were 15 multiple choice questions and 2 short response. I got slightly above average on the MC and slightly below on the second short response. I felt I did decent on the second short response, but I'm already at average score! Last test was 10% below average so feels good.
Can only get better, hopefully!
[QUOTE=Number-41;46406338]Holy fuck, calculating path integral propagators with the time-slicing method is horrible. Gaussian after gaussian after gaussian, and the expression gets worse in every single iteration. :v:
It's pretty neat though, I'm getting the financial version of path integrals, instead of the QM formulation (well, I guess it's not neat for you QM folks).
Still have no idea where I'm going with my degree, I feel like I want to apply it in an unusual way, i.e. not go into plain "nature research" but for example financial stuff, or computational stuff, I dunno...[/QUOTE]
I started reading Zee's QFT textbook (Zee is a damn good writer, so clear) and he builds it up from path integrals. Gaussians everywhere man.
Anyone here familiar with CFD? I and a few of my classmates have to work on a rocket injection system, mainly the mixing quality of oxidizer and fuel. I have a few teachers who know a bit about it, and I guess I'll learn quite a bunch by reading some relevant publications. What's the main thing to keep in mind if I want to get realistic results?
[QUOTE=_Axel;46459161]Anyone here familiar with CFD? I and a few of my classmates have to work on a rocket injection system, mainly the mixing quality of oxidizer and fuel. I have a few teachers who know a bit about it, and I guess I'll learn quite a bunch by reading some relevant publications. What's the main thing to keep in mind if I want to get realistic results?[/QUOTE]
A number of modern CAD programs had 3D CFD addons.
Can someone explain why free neutrons decay with a half-life of about 11 minutes? Why do free neutrons decay and neutrons as part of an atomic nucleus (say H-2 or He) do not?
Quick question
All EM radiation has the same speed (c)
So why is c called the speed of light and not the speed of electromagnetic waves? Is it a simplicity thing?
[QUOTE=Mallow234;46614128]Quick question
All EM radiation has the same speed (c)
So why is c called the speed of light and not the speed of electromagnetic waves? Is it a simplicity thing?[/QUOTE]
Electromagnetic waves are light, so I guess its easier to say speed of light
So Walter Lewin was found to have sexually harassed an MIT student and now his famous video lectures are being taken down.
[url]https://newsoffice.mit.edu/2014/lewin-courses-removed-1208[/url]
[IMG]http://i.imgur.com/Nkb9wcY.png[/IMG]
I find this a scary problem.
[editline]19th December 2014[/editline]
After some thinking I come up with L*A with A the crossection of the sugar stream and L the height from which the person is pouring. But that seems too simple.
[editline]19th December 2014[/editline]
That would be the case if there was no gravity and somehow the sugar emerged from the bag at some velocity. I think the longitudinal density of the sugar "beam" decreases as it falls further. Possibly proportional to exp(-gz) as the density is dm/dV and dV will stretch linearly if you consider the distance between two particles released at different times. I'll try it with some rigour soon.
[QUOTE=Number-41;46751965][IMG]http://i.imgur.com/Nkb9wcY.png[/IMG]
I find this a scary problem.
[editline]19th December 2014[/editline]
After some thinking I come up with L*A with A the crossection of the sugar stream and L the height from which the person is pouring. But that seems too simple.[/QUOTE]
it depends on the height you're pouring from, which isn't mentioned in the question. it makes it sound like you can directly get a numerical answer in kilograms and I don't think you can.
I think the mass of sugar that ends up on the scale is 1kg + flow rate * time, where the time in this case is the time it takes for a single particle to fall through a height h.
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