So I meant to mention this a while ago, but a month or two ago I went to the Roanoke Science Museum and they had an Omniglobe:
[url]http://sci.odu.edu/oceanography/geoids/images/omniglobe1.png[/url]
It was super neat. You can project all sorts of geographical maps of Earth and other planets and moons, but the most interesting thing to me is that you could project the Planck CMB data (as well as WMAP and COBE for comparison). I've never seen it on a sphere before. It was real fuckin' neato. Also, I was surprised that they had the Planck data so soon.
Just found these in my grandpa's old belongings. Mint condition.
[t]http://puu.sh/9LL0m/fce10780f2.jpg[/t]
[URL="http://particlefever.com/"]Particle Fever[/URL] is available Tuesday on iTunes. I can't wait to check it out.
[QUOTE=Falubii;45250740][URL="http://particlefever.com/"]Particle Fever[/URL] is available Tuesday on iTunes. I can't wait to check it out.[/QUOTE]
Looks very neat.
So just snapped up a copy of Dirac's [I]Principles of Quantum Mechanics[/I] (4th Ed) for $15...
Has anyone here read through it? How penetrable is it to a motivated 2nd-year?
It depends what you've already taken.
Arguing with people on reddit and getting downvoted because people people were claiming that being in orbit isn't being in "zero gravity," while I disagreed.
While generally I hate people who constantly flaunt their (often inaccurate) knowledge of physics and math for no reason, once in a while I love getting disagreed with because people don't understand the more modern perspective. It gives me the same kind of persecuted correct dude boner that I bet Einstein got when he was first getting criticized for GR.
Physics: 25% for the good of mankind, 50% for your insatiable curiosity, 25% ego-stroking.
Did they just not understand the definition of zero G? Am I missing something?
They were stuck in the whole, "But there's still a nonzero gravitational field!" mindset. No concept of geodesic motion.
It's been a while since anyone's posted in here, so here's a video of Neil Tyson misstating the twin paradox.
[video=youtube;n2s1-RHuljo]http://www.youtube.com/watch?v=n2s1-RHuljo[/video]
It took me some time to make sense out of the picture on the cover of this textbook.
[img]http://www.uscibooks.com/taycm.jpg[/img]
Hah. I never got that before. Physicists all seem to have that kind of sense of humor because then there's this:
[IMG]http://i60.tinypic.com/169s13q.jpg[/IMG]
What do you get when you cross an elephant with a mouse?
[sp]|elephant|*|mouse|*sin(θ) in the direction orthogonal to the elephant and the mouse according to the right hand rule.[/sp]
Solid start to the semester.
[url]http://physics.stackexchange.com/questions/24309/plutos-gravitational-pull-on-a-person-on-the-earths-surface[/url]
Love the top two comments on the first answer.
Hey Johnny, the [url=http://physics.illinois.edu/people/profile.asp?tomf]assistant professor[/url] leading my quantum discussion section is a string theorist. Bet you're jealous. Too bad I don't know enough to have any interesting conversations.
[QUOTE=Falubii;45830803]Hey Johnny, the [url=http://physics.illinois.edu/people/profile.asp?tomf]assistant professor[/url] leading my quantum discussion section is a string theorist. Bet you're jealous. Too bad I don't know enough to have any interesting conversations.[/QUOTE]
There were 4 string theorists at my university and my GR professor was one so no I am not jelly.
[IMG]http://puu.sh/bhsf7/b3d886dfc9.png[/IMG]
I'm so screwed for this task (Metropolis Monte Carlo simulation of electrons in a parabolic potential in Fortran), but at least it delivers pretty pictures...
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.
Read bill bryson's A Short History on Nearly Everything
Good read, quite enjoyed it, my (casual) love for physics has taken a back seat recently though due to moving out of home, working a job and studying comp sci full time.
Maybe one day I'll come back to physics and start learning again, it's quite fascinating, hopefully string theory gets further along by then (or they find a better theory and get that up to snuff)
[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]
It's [URL="http://stackoverflow.com/questions/13078736/fortran-vs-c-does-fortran-still-hold-any-advantage-in-numerical-analysis-thes"]fast, apparently.[/URL].
I don't know nearly enough about it to form a decent opinion, but coming from C++/C I don't like it that much. It's plain ugly cody, the formatting options to print output look like gibberish on first sight (it's a subjective remark, I admit). It feels archaic and restricted.
I guess it's also a bit of a leftover (code inheritance) from earlier days (my task is based on a paper from 1994, the code they gave me was F77 instead of F90 :v:), combined with the fact that it really is pretty good for not too complex numerical computations. Both in terms of speed & adaptation to mathematical notation. It's just a good tool for a specific problem, i.e. molecular dynamics, astronomy (?), simulations in general...
My preference still goes to C/CUDA for physics programming. It might be a bit slower (unless you can use the GPU, then it's blazing fast) but it can take on so much more diverse problems.
[QUOTE=Empty_Shadow;45866901]Maybe one day I'll come back to physics and start learning again, it's quite fascinating, hopefully string theory gets further along by then (or they find a better theory and get that up to snuff)[/QUOTE]
Maybe there will be another string revolution! (in a decade or two)
Apparently you can gravitationally lens gravitational waves.
So I'm sorry for bringing this kind of shit into this thread, but keeping with my dream of pushing myself to be the best astronautical engineer I can be I'm taking honors physics this quarter. So far its been all review of AP Physics at even faster pace and with far more difficult problems, but I'm absolutely stuck on this impulse problem. Also my damn fault for procrastinating on this, I faaaaar underestimated how long this one problem would take me.
Anyways, the problem is the following:
[quote]A tugboat of mass [I]m[/I] = 20,000kg pushes a barge with a mass of 80,000kg so that starting from rest, they reach a speed of 2.0m/s after 10s. Assume that the effects of gravity are canceled out, and that friction is negligible. The front bumper on the barge may buckle if a force of more than 150,000N acts on it, and its propeller may fracture if it is asked to provide more than 250,000N of force.[/quote]
Standard enough, seems fairly easy. First actual question is "How much impulse did the contact interaction with the tug give the barge?"
J=Δp, which I'm calculating in this case as 160,000kg*m/s (Δp=(80,000kg)*(2.0m/s), since initial momentum is zero due to zero velocity).
It then goes on to say;
[quote]Argue that your answer implies that the barge's contact interaction with the tug must have exerted a force of magnitude 160,000n on the barge and explain....[/quote]
WAIT. WHAT!?!? Force is equal to impulse divided by time, (160,000/10=16,000N) and 160,000N implies that the impulse is actually 1,600,000kgm/s, further reinforced by the next section saying that the tug receives this much impulse from the barge over this time interval.
I really don't understand how this works, or where it came from. All my answers are off by an order of magnitude of what is given in the questions themselves, and I've been on this one problem alone for the last 4 hours. If I hadn't been so dumb and procrastinated this to the last damn second since i thought it would be easy, I could've gone to the study center but now I'm going to get a failing grade on my first homework assignment most likely.
[QUOTE=paindoc;46121049]So I'm sorry for bringing this kind of shit into this thread, but keeping with my dream of pushing myself to be the best astronautical engineer I can be I'm taking honors physics this quarter. So far its been all review of AP Physics at even faster pace and with far more difficult problems, but I'm absolutely stuck on this impulse problem. Also my damn fault for procrastinating on this, I faaaaar underestimated how long this one problem would take me.
Anyways, the problem is the following:
Standard enough, seems fairly easy. First actual question is "How much impulse did the contact interaction with the tug give the barge?"
J=Δp, which I'm calculating in this case as 160,000kg*m/s (Δp=(80,000kg)*(2.0m/s), since initial momentum is zero due to zero velocity).
It then goes on to say;
WAIT. WHAT!?!? Force is equal to impulse divided by time, (160,000/10=16,000N) and 160,000N implies that the impulse is actually 1,600,000kgm/s, further reinforced by the next section saying that the tug receives this much impulse from the barge over this time interval.
I really don't understand how this works, or where it came from. All my answers are off by an order of magnitude of what is given in the questions themselves, and I've been on this one problem alone for the last 4 hours. If I hadn't been so dumb and procrastinated this to the last damn second since i thought it would be easy, I could've gone to the study center but now I'm going to get a failing grade on my first homework assignment most likely.[/QUOTE]
Could be a typo in the question, that happens all the time here. If something doesn't match up and you're sure about this, refute the question and/or point out different ways this may have happened.
(For example the tugboat could have waited 9s before starting to push for the 10th, or could have exerted an irregular push. An examination of the front bumper should provide the answer.)
There also seems to be an additional oversight, since at least to me it would make more sense for the tugboat to have the front bumper and propeller in the first part... Unless they are in reverse or something.
Yeah, it was a typo in the question and I never reciewved that news because my student email doesn't work on my desktop. Checked on my surface and thhe corrected numbers were sent out in an email. OH well
So I get to do a problem (one of the "simple" ones) for my honors physics course that involves finding out how difficult it is to find new planets based on gravitational disturbances of the center of mass of a system.
This is going to be a fun problem! (hopefully)
I do fear the rich-context problem though
Do you need to calculate how sensitive the required spectrometer would need to, or something different?
[QUOTE=Falubii;46173816]Do you need to calculate how sensitive the required spectrometer would need to, or something different?[/QUOTE]
No, we used the gravitational disturbance method of a star 8.1ly away and had to find the systems center of mass and how many milliarcseconds (1/3,600,000 of a degree) its star was from the systems center of mass, and whether or not it was straightforward using this method since atmospheric disturbances blur a star to a 250mas size blob.
Its not. At all.
[QUOTE=paindoc;46178139]No, we used the gravitational disturbance method of a star 8.1ly away and had to find the systems center of mass and how many milliarcseconds (1/3,600,000 of a degree) its star was from the systems center of mass, and whether or not it was straightforward using this method since atmospheric disturbances blur a star to a 250mas size blob.
Its not. At all.[/QUOTE]
The disturbances from the planet should have an orders of magnitude lower frequency than the atmospheric disturbances though, meaning you should be able to correct for the latter with enough samples.
Unless there's a systematic error of course, which I have no idea about in this context.
[QUOTE=Tamschi;46178183]The disturbances from the planet should have an orders of magnitude lower frequency than the atmospheric disturbances though, meaning you should be able to correct for the latter with enough samples.
Unless there's a systematic error of course, which I have no idea about in this context.[/QUOTE]
According to the text after the question explaining where he got the data for the question from, that is exactly what the man who did it did. He collected a bunch of data of disturbances to prove the presence of the planet around Lalande 21185. It was a half century's of data worth of measurements of the stars position relative to distant stars
[editline]7th October 2014[/editline]
Also my textbook is great, one problem featured this excerpt:
[quote]"You are about to take another measurement of the peaks angle from the horizon, but your first mate, walking by, spills hot coffee on your back, you drop your transit on the deck, and it breaks. You severely cuss out the first mate and take the transit to the chief engineer, who says it will take 3 days to fix ("Ye canna expec' me to work miracles, Cap'n!" he says)[/quote]
There are tons of references and jokes embedded in the end of chapter problems, and some in the in-chapter examples as well
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