Below are the 20 most recent journal entries recorded in physics, the science of everything's LiveJournal:

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Friday, August 22nd, 2008
8:13 pm [esicardi]	Paper requested Has anyone access to this paper? W. Kohn, "Image of the Fermi Surface in the Vibration Spectrum of a Metal", Phys. Rev. Lett. 2, 393 - 394 (1959) http://prola.aps.org/abstract/PRL/v2/i9/p393_1 If you have it please email it to me Thanks a lot in advance. :) Cross posted to _scientists_ Edited: Got it! Thanks a lot to ellimist! *hugs* (2 Comments |Comment on this)
Wednesday, August 20th, 2008
5:18 pm [krilltish]	Help Normally, I am not that bad at physics.  However, oddly enough, certain concepts in chemistry are throwing me for a loop.  [.a'o .a'u.] I believe that I will eventually be able to work my mind through them.  But, I cannot for the life of me undestand electron configuration.  Could someone please explain it to me?  Below, I have a quote taken from the English Wikipedia talk page about electron consideration that, although I did not write it, basically sums up one part of my problem: "Even after reading this article, I have a do not understand why the orbitals must be distinguished by letter (s, p, d, f, g) during notation and what the effects of this (the meaning of the representation provided by the letters, seeing as how different random squiggles being used probably does not affect quantum mechanics) are." If anyone can help me, I would greatly appreciate it.  [mu'o mi'e .kryltyc] (29 Comments |Comment on this)
Tuesday, August 19th, 2008
2:09 am [dkogan]	tunnel through the earth Suppose you drill a tunnel straight through the center of the Earth and out the other side. What will the tunnel's atmospheric pressure conditions be at the center of the planet? Assume the tunnel walls are strong enough and insulated enough to completely isolate the passage from the core's heat and pressure. Edit: This isn't homework, so I'm not looking for an exact answer... I'm just curious what the ballpark would be. Would the air liquefy? Would the pressure be zero? Would it be hot? Cold? (92 Comments |Comment on this)
Friday, August 15th, 2008
2:46 pm [iconoclass]	What is Science? "Science is what scientists do." Agree or disagree? (67 Comments |Comment on this)
Sunday, August 3rd, 2008
5:28 pm [saturn92103]	gravitational time dilation I'm not a physicist (or a physics student) but I read a fair amount of physics and I have a question as I read Susskind's new book, The Black Hole War. I have a fundamental understanding of why differences in relative speed affect time but I'm having a difficult time understanding gravitational time dilation. I get the general principle (time passes more slowly in higher gravitational fields) but is there a non-mathematical way to to explain why this occurs? (2 Comments |Comment on this)
Friday, August 1st, 2008
9:58 am [dlakelan]	Feynman water jet experiment Everyone who's read Feynman's popular works remembers the water sprinkler experiment where he blows up a carboy accidentally while at Princeton. Feynman is careful not to give away the answer to how the sprinkler turns... I've tried answering this theoretically several times and depending on how you analyze it you get different results... that's the point I guess... the truth is that the sprinkler only goes one way... and if you want to see which way, you can watch the experiment on youtube *SPOILER ALERT* In the comments, I'm hoping some of you will talk about how you think about this experiment both ways to analyze it that don't work, and ways to analyze that do work. What is the actual effect? Why don't some of the other methods of analysis work? It's a fun problem. (4 Comments |Comment on this)
Monday, July 28th, 2008
12:47 am [njyoder]	Nikola Tesla's "Earthquake Machine" and "Wireless Power" OMG TV INSPIRED POST AGAIN OMG Two different shows on the History Channel about Nikola Tesla made me feel ashamed for their productions. The self-reported (by Tesla himself) urban legend that he created an "Earthquake Machine" that with a mere peak 5 pounds of force at its resonant frequency, could cause a decent sized steel building to shake as if there was an earthquake. MythBusters tested that and debunked it in episode 60 (season 4). I have question concerning claims made Tesla regarding his Magnifying Transmitter (a Tesla Coil modified to transmit power wirelessly) that was tested in Colorado Springs( his Colorado Springs Notes 1899-1900 would have details). I can't find the primary source claims, but tertiary sources state that Tesla could light a bulb 30 meters away from the transmitter. It's estimated to run between 4.5 million to 5 million volts. NOAA's website contains information on the air pressure, humidity, and temperature of Colorodo Springs. For the sake of this, you can oversimplify and idealize some things. How would one begin to calculate how far out someone could light a 60-watt light bulb fully given the various parameters of this magnifying transmitter (you can just make up or guess what information isn't there, if possible)? Note 1: The Wardenclyffe Tower is an uncompleted, bigger version of the Colorado Springs transmitter. He ran out of funding before it cold be completed and now only part of the original building stands--it's connected to some kind of photography company that now owns the property. Note 2: I randomly came across new research on "WiTricity" by MIT scientists. Using near field induction, they could power 60-watt light bulb from 2 meters away with 40% efficiency. (7 Comments |Comment on this)
Friday, July 25th, 2008
5:45 pm [thehibiscus]	Could anyone please shed some light on this.. The question is: Two pieces of optically flat glass (n = 1.5) touch at one edge and are separated by a thin stretched fibre at the opposite edge. Light of wavelength 500 nm is shone from above and 100 dark fringes are counted. The air between the glass is now replaced by water (n=1.33). How many dark fringes are now observed? The only thing I know is... d sin x = lambda * m Help please. (3 Comments |Comment on this)
Monday, July 21st, 2008
9:56 pm [mvak]	english-thai physics glossary A bit of a strange request: I'm teaching a summer class on nuclear physics for high school students, and I have a student from thailand who has pretty limited english skills.  I'd like to help her out by getting some kind of english-thai glossary of physics terms, or even a full-blown dictionary of such things; I've seen something like this for japanese-english.  If anyone knows of anything like this, please let me know--thanks in advance! (2 Comments |Comment on this)
4:08 pm [thehibiscus]	A little help would be MUCH appreciated The question in my problem set states: Astronauts visiting Planet X have a 2.60 m long string whose mass is 5.00 g. They tie the st ring to a support, stretch it horizontally over a pulley 1.50 m away and hang a 1.60 kg mass on the free end. Then the astronauts begin to excite standing waves on the string. Their data show that standing waves exist at frequencies 64 Hz and 80 Hz but not in between. What is the value of g, the acceleration due to gravity on Planet X ------------------------------------ The answer is 2.77 m/s^2. ----------------------------------- How do I arrive at this answer? The steps I followed were.. L = (n/2)  x wavelength And after I found the wavelength, I would use: velocity = frequency x wavelength Once I got the velocity, I could use: velocity = sqrt (tension = mass x gravity)/(linear density) Unfortunately, no matter how I tweak the numbers, I still do not arrive at the correct answer. Please help. (5 Comments |Comment on this)
Sunday, July 13th, 2008
6:53 pm [njyoder]	Jesus Problem I am watching this thing on the science behind crucifixion, and they made a physics-related claim regarding a person hanging (mostly about Jesus) on the cross which I found puzzling. It's been a while since I've done this, so I'm probably missing something horribly simple. Basically, they were trying to show the forces on the hands themselves due to the weight of the body (Jesus), with the hands being fixed in place by nails. Ignore that the weight would cause their hands to be torn through--that's what the demonstration was supposed to show. So for the purpose of simplicity, they are attached by ropes. EDIT: Alpha = beta. The length of the "arms" are equal. Assume that the "arms" are directly attached to the center of mass of Jesus, rather than the slightly odd way I drew it--with an additional rope connecting to the two "arms" (this is actually more like the test setup which used force sensors at the "fixed points" and weights attached to both of them via ropes). The idea is to find what F1 and F2 (which are the forces on the "hands") are relative to the weight (F3=W=m*g) of Jesus. ( OMG SPOILAR WANRING ZOMG this is the answer they gave... ) Random, unrelated question: has anyone ever seen "omg" (i.e. o*m*g) as part of a physics problem? Another random question: what do you recommend for drawing physics related diagrams, especially statics/dynamics/related crap? (26 Comments |Comment on this)
4:01 pm [amatol]	degrees of freedom In my thermodynamics class we are talking about computing degrees of freedom (for internal energy or U=f/2kT, f being degrees of freedom) and I get it for monotomic and diatomic gasses and solids, but I am rather confused as how to do it for a liquid. I am trying to figure it out by counting the quadratic terms of the energy, which works nicely for the above cases (monatomic, etc.). But I am not sure of the structure of water (beyond the fact it is two hydrogen attached to an oxgen atom) and how to figure out how to compute all the components to its energy or basically try to conteplate all the possible ways it can move/rotate/etc. I have browsed online and my text and all references I see are for ideal gases or solids... so any suggestions for where to look or explanations are greatly appreciated. (I have a feeling this is where taking a chemistry class would have come in handy) (2 Comments |Comment on this)
Saturday, July 12th, 2008
11:15 pm [elddiremsiht]	Hello, I'm a very intrigued 16 year old, but a bit of a physics noob, so bear with me. My school hasn't yet offered a physics class for my age, so all that I know is from reading and studying I've done on my own. I just have a few questions about probability waves, I'm sorry if they sound stupid. I understand the principle that when an object is not being observed, it exists as a wave of probability. But what exactly does this wave represent? All of the possible locations of the object, or more? Can it represent the possible states of the object? Does this apply to the old addage, "If a tree falls down in the forest and no one's around to hear it, does it make a sound?" In this case, would the tree simultaneously make a sound and not make a sound? Or does the example just not apply? Do waves of probability stem only from the Heisenburn uncertainty principle? Is it known why the differences between an observed particle and an unobserved particle exist, like in the double slit experiment? How does the particle "know" it's being observed? Sorry for the multitude of questions, and thanks in advance for your time in addressing what are probably really dumb questions. (16 Comments |Comment on this)
Sunday, July 6th, 2008
10:56 pm [paladinmt]	I call bullshit The End of Theory: The Data Deluge Makes the Scientific Method Obsolete (13 Comments |Comment on this)
Friday, July 4th, 2008
2:56 pm [wwidsith]	Given that opposite charges attract, what stops an electron from crashing into the positively-charged atomic nucleus? (I'm assuming it's not analogous to a planet orbiting a star - though perhaps it is - because electromagnetic force is so much stronger than gravity, and anyway an electron isn't really a particle at all.) (25 Comments |Comment on this)
Wednesday, July 2nd, 2008
5:29 pm [calysto]	Space Technology in our Every-Day Lives I was having a discussion with a good friend when she challenged me to tell her how CERN's LHC will benefit mankind. She's a creationist, so talking about discovering how the universe came into being was pointless. As was bringing up things like string theory, particle physics, dark matter, and the Higgs particle. So instead I decided to compare the LHC to the space program. Some people have always claimed the space program is a useless waste of money with no practical value to humanity. So I collated a list of technologies and improvements which have come out of the space program which improve our every-day lives. I'm posting this list here, so that you guys can use it in similar discussions with other people when they ask what's the point of pure science endeavors like the LHC... ( Here's the list... cut, due to length ) Here are my source articles, which include specifics on each of the above and how they relate to the space program: [1] [2] [3] [4] (24 Comments |Comment on this)
Monday, June 30th, 2008
8:29 pm [calysto]	Sometimes... Sometimes I wonder if the human race deserves progress... Luddism is nothing new, nor is the type of luddism which fears particle colliders, but as CERN's massive LHC prepares to come online the fears -- and lawsuits -- are coming to a head. [CNN's article] OMG! teh black holz will swallow us all! (21 Comments |Comment on this)
Sunday, June 29th, 2008
3:55 pm [oh_brianna]	So I'm having trouble figuring out this problem for my college physics class: ( The Rest is HERE... ) (6 Comments |Comment on this)
Wednesday, June 25th, 2008
10:01 am [myliverandlungs]	momentum help. can't remember the exact problem verbatim but heres how it is setup a car. 1200 kg. goes 25 m/s positive x-direction. a truck. 1800 kg. goes 15 m/s positive x-direction. car crashes into truck. 1-dimensional elastic collision. find final velocities (not speed) of each car and truck. you're supposed to get 13 m/s and 23 m/s (i think? if not, somewhere close to that value) both toward positive x-direction. so i set up the good old conservation of momentum equation, elastic collision, and ended up with the following: vfinal car = (stuff in terms of vfinal truck) ... (equation 1) vfinal truck = (stuff in terms of vfinal car) ... (equation 2) but i can't solve the equation. instead of getting a magnitude of the velocities, i ended up getting this: vfinal car = vfinal car vfinal truck = vfinal truck which doesn't help. any ideas? (7 Comments |Comment on this)
Sunday, June 22nd, 2008
10:09 pm [stutterbird]	Homework Questions I've been having some trouble with the homework our professor assigned this weekend, since I missed a couple of class days for college orientation. So, I'm a little behind and would really appreciate help with the following questions. I think if I have a starting point and some general directions, I should be able to manage. ( Suppose a horse leans against a wall... ) ( A child slides up an icy street... ) For reference, I'm working out of College Physics, Second Edition (Paul Peter Urone), Chapter 4: Dynamics, Newton's Laws of Motion and Chapter 5:Statics, Torque, and Elasticity. Thanks in advance! (3 Comments |Comment on this)