Physics
esiegel | April 10, 2009Everyone who's taken physics at some point knows about the Right Hand Rule. There are two versions. If you have a wire carrying an electric current, you point your thumb in the direction of the current and your fingers "curl" in the direction of the magnetic field.
The other version is that if you have two out of the following three -- current, magnetic field, and a force -- the right hand rule can help you find the direction of the third one that gets induced from the other two:
Well, there's one really annoying thing about this rule: it requires the current to be moving positive charges!…
drorzel | April 9, 2009Sabine Hossenfelder from Backreaction has landed a job as an assistant professor at NORDITA. That's good news any time, but especially in the current climate.
And going Sabine one better, Mary at View from the Corner has both defended her thesis and gotten a job at the same company as her husband. Way to solve the two-body problem, Mary.
Congratulations to both of them. And if you have happy job news to report, consider this a Happy Job News Open Thread.
drorzel | April 8, 2009New ScienceBlogger and American Gladiator Ethan Siegel of Starts With a Bang has a couple of nice posts about dark matter and how we know it's there (one, two).
These posts reminded me that I never did follow up on the discussion following my post about Magic World Media, who are looking to publish kids' books about science, and seeking kindergarten-level explanations about dark matter and dark energy. A few commenters expressed doubts about whether this could or even should be explained to kids at that level.
I don't have any strong feelings about the "should" question, but it seems to me…
rallain | April 7, 2009I recently posted a tutorial on using Logger Pro for video analysis. Why did I use Logger Pro? Why not Tracker Video? Here is a quick comparison of the two.
Logger Pro
In the previous tutorial, I used Logger Pro. The primary reason was that the tutorial was for a lab course. The students were already familiar with Logger Pro. Here are some of the pros of Logger Pro.
Fairly straight forward to use.
Good graphing and curve fitting utilities built in.
Integration with data from other sources. If you video a ball falling and also use a motion detector, you can "sync" the data.
Not really…
rallain | April 6, 2009Cats can be entertaining - especially when they are someone else's cat and that someone made a video. Really, this post is about analyzing video with Logger Pro (in a tutorial type fashion). I just happens that I chose this cat video to analyze. Here is the video:
I am going to look at the part where the cat gets on the fan. I will try to step through the analysis so you can do your own.
Get the video
Actually, the first step is to find a video. YouTube has tons of stuff. Also, you could make your own video with a camera. A couple of things to make your life easier:
A non-zoom video…
drorzel | April 6, 2009Over at the First Excited State, the quasi-anonymous proprietor laments the tendency of basketball replays to focus on the shot rather than the play that set up the shot, and compares this to a maddening student habit:
Students in introductory physics classes inevitably place too much focus on the final numerical answer of the problem, which in reality is the least important part. I graded a quiz last week where I spent way too much time trying to decipher the numbers the students wrote down, because they placed the numbers in their equations rather than writing them clearly with the symbols…
rallain | April 3, 2009I found this video to be very entertaining.
Dry Ice is LEEEEEEATHALLY DAAAANGEROUS? - These bloopers are hilarious
William Beaty's site has tons of great stuff - http://www.amasci.com/
amillikan | April 2, 2009In an article in The New York Times Magazine Sunday, Freeman Dyson—best known for his work in theoretical physics—discussed his belief that climate change is an issue that should be approached with skepticism. ScienceBloggers responded with thoughtful consideration. Dyson stated in the Times piece that while prevailing dogmas about climate change may be right, they deserve to be challenged. "That they do," conceded ScienceBlogger James Hrynyshyn from The Island of Doubt. "My only quibble is they are best challenged by those with a good grasp of the latest findings."
drorzel | April 2, 2009Physics World this month has a nice article by Robert Crease on the strategies used in popular physics books, drawing on a study of popular books by Elizabeth Leane (Reading Popular Physics, much of which is available via Google Books). He talks about three different strategies that she identifies, and how they're employed in different fields. I was particularly amused by this:
Explaining quantum theory, for instance, seems both to require and to shipwreck metaphors — for what is “down there” just does not behave like what is “up here”. A common tool is to anthropomorphize, personifying…
drorzel | April 2, 2009The spring round of the Adopt-a-Physicist outreach program will begin soon. I did this in the Fall, and it was a good experience, so I've registered myself again.
The program pairs volunteer physicists with high school classes, and provides a web forum in which students can ask questions about physics and careers in physics. Back in the fall, the students I communicated with asked smart and interesting questions, and it was a pleasure to talk to them.
If you have a degree in physics (undergraduate or graduate), and would like to help encourage high school students to consider physics, you…
drorzel | March 31, 2009This is the final report on my modern physics class from last term, covering the last week of classes, which generally deal with nuclear and particle physics. This was actually three-and-a-bit classes, because I lost one class to a nasty cold a few weeks earlier, and used part of the lab period to make up for it.
Class 28 was actually taught by a colleague of mine (thanks, Rebecca!), because Kate and I were in Boston for her father's wake. She taught off my notes, though, so I'll still report it as if I did the class.
This class opens with a brief return of the historical treatment of the…
drorzel | March 31, 2009In the last course report post, we dispensed of atomic and molecular physics in just three classes. The next three classes do the same for solid state physics.
Class 25 picks up on the idea of basic molecular potentials from the end of the previous class, and uses that to introduce energy bands in a qualitative manner. Bringing two atoms together splits the electron levels into two states, adding a third adds more closely spaced levels, and so on. Every time you add more atoms, you add more closely spaced energy levels, and as you approach truly macroscopic systems, those states run together…
rallain | March 31, 2009What is a fake force? A fake force is one of those forces that introductory texts tell you aren't real - like centrifugal force. They aren't real in the sense that they are due to one of the fundamental interactions. Basically, introductory texts (and even blogs like this one - not a bad summary of real vs. fake forces) attack the centrifugal force. This is because it is so common for students to want to use these faux forces in the wrong way. Better to just not use them at all.
Anyway, there are times when faux forces are awesome. Just to be clear, a faux force is needed to use normal…
drorzel | March 31, 2009I got way behind on my reports from my Modern Physics class-- the last one was over month ago, and the class has since ended. There's enough material left to be really awkward as a single post, though, so I'm going to take my cue from Brandon Sanderson and split it into three parts.
The remaining material is from the sprint-to-the-end "Applications of Quantum Mechanics" portion of the class, and breaks into three roughly equal chunks. The first of these is dealing with atomic and molecular physics.
Class 22 presents the full quantum model of Hydrogen, starting from the Schrödinger equation…
drorzel | March 30, 2009Today is the first day of Spring term classes, which means there's one obvious question to ask:
What am I forgetting?
I've spent the last few days alternating baby duty with frantic class prep, and I think I've got everything ready. I'm bound to be forgetting something, though. So what is it? What's the thing I forgot to do that's going to lead to a mad scramble just before the class starts at 10:30?
drorzel | March 27, 2009OK, "quiz" isn't really the right word, because I don't know the right answer. But here's something weird that I noticed a while ago, and since I needed an excuse to fool around with video a bit, I thought I'd shoot some pictures of it:
Here's the deal: My cell phone is gently curved on one side. If I put the phone on a table with that side down, it will spin reasonably freely, with very little effort. If I try to spin it fast, though, it very quickly develops a pronounced wobble that damps out the spin very quickly. You can see it in the YouTube video above.
So, the question is: Why does…
drorzel | March 27, 2009The Tuguska event of 1908 is one of the most frequently "explained" events in recent history, trailing only the Kennedy assassination. The arXiv blog reports on the latest explanation of what knocked down all those trees without making a giant crater:
Now a new analysis by Edward Drobyshevski of the Russian Academy of Sciences in St Petersburg Russia claims to have solved these problems. Drobyshevski concludes that the object that hit in 1908 was a comet (as have many scientists before him). But unlike the others, he has been able to calculate that this comet hit the Earth's atmosphere almost…
drorzel | March 26, 2009As a scientist with a blog, I am apparently contractually obligated to link to the New York Times Magazine profile of Freeman Dyson. If I don't, they'll take away my privileges as a scientist. (Of course, since those consist mostly of the right to review grant applications for the NSF, maybe it'd be worth the risk...)
I don't mind linking to it, though, because it is a nice piece of work. The focus is mostly on Dyson's (relatively) recent climate skepticism, because that's a high-profile offbeat opinion to have these days, but it gives a nice sketch of his background and accomplishments.
One…
pontiff | March 26, 2009Lately I've been giving a lot of thought to a question that I'm nearly constantly asked: "So...[long pause]...are you a physicist...[long pause]...or are you a computer scientist?" Like many theorists in quantum computing, a field perched between the two proud disciplines of physics and computer science (and spilling its largess across an even broader swath of fields), I struggle with answering this question. Only today, after a long and torturous half year (where by torture, I mean interviewing for jobs, not the eerily contemporaneous fall of the world's finances) in which I have been…
drorzel | March 26, 2009I'm teaching the intro mechanics course next term, starting on Monday, and my colleagues who just finished teaching it in the Winter term used WebAssign to handle most of the homework. They speak very highly of it, so I'm probably going to use it next term.
I'm curious to know what other people think, though. The reasons my colleagues give for liking it sound good from a faculty perspective, but I'm not sure how well it would go over with students (for one thing, it's another $15 on the price of the text). Does anybody have experience with using WebAssign, either as a student or as an…