Physics
drorzel | August 31, 2010Over in Discover-land, Razib has a couple of posts about the content of science blogs, based on an analysis of the content of the top science blogs according to Wikio. Razib's second post is sparked by a pointed question from the author of the original study:
I'm now curious to find out why there are no 'popular' blogs in certain subjects. Do working condensed matter physicists who want to engage with the public write about astrophysics? Or are astrophysicists the only physicists who want to blog for the public? Or does the public only read astrophysics blogs?
This is, of course, an obvious…
drorzel | August 31, 2010Sunday was a really long day around Chateau Steelypips, and I couldn't see staying awake to watch the premiere of Phil Plait's Bad Universe on the Discovery Channel, so I'm way late in writing about it. I DVRed it, though, and watched it last night.
The theme of the premiere/ pilot was killer rocks from out of space, and focused on Phil getting his MythBusters on to test various ideas about asteroid or comet impacts and how to stop them. They blew up a scale model, shot projectiles into various types of rock to simulate nuclear bombs or kinetic impacts, all in the name of testing what would…
rallain | August 31, 2010Reader Fruity was the first to correctly name this device - on just the 9th comment. Impressive. Honestly, when I found this thing I had no clue. I asked other physicists and none of us were sure. However, I did find the answer. Let me show you my secret.
I don't know how old this thing is, but it is old. When I open it, my nose and eyes get all tingly - probably from the mold. Here is that apparatus in the book (tome):
I can't show you the whole page because it has other stuff of awesomeness that I want to show you later. But, I can show you the description for that item.
I am…
drorzel | August 30, 2010Last week, John Baez posted a report on a seminar by Dzimitry Matsukevich on ion trap quantum information issues. In the middle of this, he writes:
Once our molecular ions are cold, how can we get them into specific desired states? Use a mode locked pulsed laser to drive stimulated Raman transitions.
Huh? As far as I can tell, this means "blast our molecular ion with an extremely brief pulse of light: it can then absorb a photon and emit a photon of a different energy, while itself jumping to a state of higher or lower energy."
I saw this, and said "Hey, that's a good topic for a blog post…
drorzel | August 27, 2010I'm pretty sure I've used this topic before, but not with PollDaddy. And while I really ought to do a ResearchBlogging post today to make it a clean sweep for the week, I just don't have the energy.
So here's a poll: what's your favorite fundamental force?
What's your favorite fundamental force?online surveys
Those of us with corporeal existence should restrict our answers to the low-energy condition of the present material universe, not any of the higher energy unification scales.
rallain | August 27, 2010It would be nice if I could come up with a good rhyme for grade to fit this title.
One of my brothers is a biochemistry faculty at Appalachian State University (hint - he is the one with the same last name that I have). We were talking (and surprisingly agreeing) that grades were dumb. What would happen if we stopped grading? Wouldn't that be awesome?
So, what would happen if there were no grades? Here are some thoughts.
We would only have one job in the class - help students learn. The second job of evaluating student understanding would only be there to help them learn more.
It would…
rallain | August 27, 2010Here is my plan. Post a "what is this" on every Friday until I run out of things. I will post the answer on Tuesday. Maybe we should start keeping points. You get more points for being the first one to get it right. You lose points for getting it wrong.
Last week was easy, but I think this is more of an appropriate level. Here it is:
Nice - it has a tag, but no part number. Honestly, this one stumped me for a while. If you have any reasonable questions, I might answer them.
rallain | August 26, 2010Might as well jump. Jump. Go ahead, jump. - Van Halen
Suppose everyone in the world got together and jumped. Would the Earth move? Yes. Would it be noticeable? Time for a calculation. Note: I am almost certain that I have done this before, but I can't find where.
Starting assumptions.
7 billion people.
Average weight: 50 kg (you know, kids and stuff)
Average vertical jump (center of mass): 0.3 meters - and I think that is generous.
Mass of the Earth: 6 x 1024 kg
Gravitational field near the surface of the Earth is constant with a magnitude of 9.8 N/kg
Ignore the interaction with the Sun and…
drorzel | August 26, 2010There's a minor scandal in fundamental physics that doesn't get talked about much, and it has to do with the very first fundamental force discovered, gravity. The scandal is the value of Newton's gravitational constant G, which is the least well known of the fundamental constants, with a value of 6.674 28(67) x 10-11 m3 kg-1 s-2. That may seem pretty precise, but the uncertainty (the two digits in parentheses) is scandalously large when compared to something like Planck's constant at 6.626 068 96(33) x 10-34 J s. (You can look up the official values of your favorite fundamental constants at…
rallain | August 25, 2010You know I wander around the intertubes, right? Who doesn't? Anyway, I saw this collection of strange google Earth images. Yeah, it is kind of dumb, but this one made me think:
That article said the image was from TechEBlog, so there is that.
I have no idea what this thing is, but it is clearly tall. How tall? Instead of searching online for info about this structure (that wouldn't be any fun), I figured I could do a quick analysis of the shadow. Here we go. First, I need to make some measurements. It turns out that Tracker Video tool for analysis is also quite excellent to use for…
drorzel | August 25, 2010The Joerg Heber post that provided one of the two papers for yesterday's Hanbury Brown Twiss-travaganza also included a write-up of a new paper in Nature on Mott insulators, which was also written up in Physics World.
Most of the experimental details are quite similar to a paper by Markus Greiner's group I wrote up in June: They make a Bose-Einstein Condensate, load it into an optical lattice, and use a fancy lens system to detect individual atoms at sites of the lattice. This lattice can be prepared in a "Mott insulator" state, where each site is occupied by a definite number of atoms. As…
rallain | August 24, 2010I might as well make a new tag called "basketball throws" because I can't stop with the analysis of these crazy basketball shots. Watch - in the end someone is going to post a video about how all these were faked (and I have said there is no clear evidence they are fake). Oh, if you want to see some shots that I am talking about - just search for Dude Perfect on youtube.
Physically, these crazy shots are possible. Time of flight in the video is comparable to a numerical model. But, the question is: how difficult are these shots? Are these one in a million? Are they easy? Are they…
drorzel | August 24, 2010Two papers in one post this time out. One of these was brought to my attention by Joerg Heber, the other I was reminded of when checking some information for last week's mathematical post on photons. They fit extremely well together though, and both relate to the photon correlation stuff I was talking about last week.
OK, what's the deal with these? These are two papers, one recent Optics Express paper from a week or so ago, the other a Nature article from a few years back. The Nature paper includes the graph you see at right, which is a really nice dataset demonstrating the Hanbury Brown and…
rallain | August 24, 2010Perhaps you have had enough time to think about the first "What is this" demo item. Here is the item in question.
It seems most of you were right on track with this one - probably because you can still buy such a device. This thingy launches a small ball horizontally while at the same time dropping a ball. It is supposed to show that the vertical and horizontal components of an object in projectile motion are independent.
It takes two balls (which I didn't have when I took the picture). One ball goes on each end and the arm is pulled back.
Update: Thanks to Kevin and Frank for pointing…
drorzel | August 23, 2010I'm a big fan of review articles. For those not in academic science, "review article" means a long (tens of pages) paper collecting together the important results of some field of science, and presenting an overview of the whole thing. These vary somewhat in just how specific they are-- some deal with both experiment and theory, others just theoretical approaches-- and some are more readable than others, but typically, they're written in a way that somebody from outside the field can understand.
These are a great boon to lazy authors, or authors facing tight page limits ("Ref. [1] and…
rallain | August 21, 2010Let's play a game. I think this will be fun. So, a couple of years ago I had the duty of organizing the physics demo room (well, "demo" is maybe not the best term). This room is quite large and there is a whole bunch of stuff in here, some of the items are very old.
There were lots of items that I knew exactly what they were. But, there were other items that made me go 'huh?'. So, here I will post an item. You post a comment regarding what you think it is and what it is used for. Some of these items I know the answer to, some I do not. Some of these pictures might just be part of a…
drorzel | August 20, 2010Johan Larson emails a suggestion for a post topic:
How many profs would it take to offer a good, but not necessarily excellent, undergraduate physics degree?
I can give you an empirical answer to this: Six.
I say that because in the course of my undergraduate physics degree at Williams, I took classes from only six different professors. Five-and-a-half, really, because one of those was half of a team-taught course. I had three-and-a-half classes with one professor, and two others for two classes each.
Of course, that's not a hard lower bound. Some have even suggested that the number could be…
drorzel | August 20, 2010It's nearly time for classes to resume, which means it's time for a zillion stories about Beloit College's annual Kids These Days List, listing off a bunch of things that this year's entering college class, who were mostly born in 1992, have always taken for granted. A sample:
1. Few in the class know how to write in cursive.
2. Email is just too slow, and they seldom if ever use snail mail.
3. "Go West, Young College Grad" has always implied "and don't stop until you get to Asia...and learn Chinese along the way."
4. Al Gore has always been animated.
5. Los Angelenos have always been trying…
drorzel | August 20, 2010In my post about how we know photons exist, I make reference to the famous Kimble, Dagenais, and Mandel experiment showing "anti-bunching" of photons emitted from an excited atom. They observed that the probability of recording a second detector "click" a very short time after the first was small. This is conclusive evidence that photons are real, and that light has discrete particle-like character. Or, as I said in that post:
This anti-bunching effect is something that cannot be explained using a classical picture of light as a wave. Using a wave model, in which light is emitted as a…
rallain | August 20, 2010Reader Jorge has also looked at these amazing basketball shots. (here is my last basketball analysis) Jorge claims that at least one shot seems fake. He is referring to the following video (at around the 2:20 mark).
ARRGH Ok, new plan. For some dumb reason, youtube won't let me embed this video. Well, here is a link - Amazing Basketball Shots: The Legendary Shots 4 (at least I can link to the right time). It is even dumber that you can't embed it, but youtube gives you the download option. Oh well.
Let me tell you the part that Jorge has an issue with. This guy on a ladder throws a…