Physics
drorzel | January 13, 2009The scare quotes in the title are to distinguish "Modern Physics" classes like the one I'm teaching this term from modern physics as a general subject, which, of course, all right-thinking people should study in depth. The question comes from a comment by Coriolis on last week's post about what "Modern Physics" is as a class:
Having passed through those classes (I'm now a grad student), I have to say I didn't see much worth in the Modern physics class (and your description of it is pretty much how I remember it, except without the relativity). It's basically in that middle ground trying to…
drorzel | January 13, 2009Or, Brian Greene Writes a Kid's Book...
This is a very odd book. It's printed on boards, like a book for very small children, but the story is a bit beyond what I would imagine reading to a normal kid of the age to want books of that format. It's too short and simple, though, to have much appeal to significantly older children, aside from the fact that the story is written over the top of 15 absolutely gorgeous reproductions of pictures of astronomical objects.
This is probably one of those objects whose cool appearance is the only real reason for the thing to exist. The pictures really are…
rallain | January 12, 2009I am not going to try and even surprise you with this. Notice the "tools:". This post is not about physics really, but something used in physics. When I get enough of these, I will put them together in a "tools" page - or you can just use the tools-tag.
Suppose you have some data. You want to plot that data and turn it in with your lab report. Your instructor (me) told you to be sure and include error bars on your graph.
What are error bars?
How do you add error bars - whatever they are?
Error bars are a way to graphically represent the uncertainty in a data point. Every time you take…
drorzel | January 12, 2009 There's been a fair bit of press for the article Subtracting photons from arbitrary light fields: experimental test of coherent state invariance by single-photon annihilation, published last month in the New Journal of Physics, much of it in roughly the same form as the news story in Physics World (which is published by the same organization that runs the journal), which leads with:
A property of laser light first predicted in 1963 by the future Nobel laureate Roy Glauber has been verified by physicists in Italy.
These stories can be a little puzzling, though. After all, Glauber got his…
drorzel | January 12, 2009There was a mix-up in textbook ordering for this term (entirely my fault), and the books for my modern physics course were not in the bookstore when the term started. I made a spare copy available in the interim, and also half-jokingly suggested buying it from Amazon rather than waiting for the bookstore to get them in. After saying that, I went to Amazon, and found that the book in question sells for $150. "That can't be right," I thought. And, indeed, it's not-- the bookstore sells its copies at the list price of $180.
I had no idea the books were that expensive, and now I feel guilty about…
rallain | January 10, 2009So, here is a video (from break.com - so you know it is likely fake).
null - Watch more free videos
If for some reason, you can not view this video, here is the plot.
Guy wears parachute and brings a portable thing like a see-saw.
Guy approaches large crane dropping a large mass repeatedly (I assume to flatten a dirt road)
Guy sneaks up an puts the see-saw under the area that the mass drops on and then stands on the other end of the see-saw.
Mass drops, guy shoots up and parachutes down.
So, why is it fake? I think the best thing is to give an analysis of the see-saw. To start this…
pontiff | January 9, 2009Scienceblogs is upgrading. This site won't allow comments from 10pm Pacific Standard Time on Friday, January 9 until...well until the upgrade is complete (possibly Saturday sometime.)
So instead of being frustrated at not being able to comment why don't you instead go waste your time by:
By reading some provocative statements about teaching over at the information processors blog.
If you need to procrastinate about preparing a referee report, you might check out Michael Nielsen's Three myths of scientific peer review
The Statistical Mechanic is back, and discussing thermodynamics,…
rallain | January 8, 2009Here is an article from Wired.com that talks about a used cooking oil generator. It's a really neat idea in that the oil is right there anyway. Here is my problem - from the article:
A new garage-engineered generator burns the waste oil from restaurants' deep fryers to generate electricity and hot water. Put 80 gallons of grease into the Vegawatt each week, and its creators promise it will generate about 5 kilowatts of power.
If you put 80 gallons of grease into the thing, that has a finite amount of energy. 5 kilowatts tells you the rate the energy is created. This would be like saying "…
drorzel | January 8, 2009A couple years ago, we revised the General Education requirements at the college to require all students to take a "Sophomore Research Seminar" in their second year. These classes are supposed to be writing-intensive, and introduce students to the basics of academic research. The specified course components are pretty heavily slanted toward the humanities-- library searches, primary vs. secondary sources, and so on-- and don't really map that well onto research practices in the sciences.
A colleague in engineering managed to do a really interesting project-based class, though, and since…
drorzel | January 8, 2009Over at the theoretical physics beach party, Moshe is talking about teaching quantum mechanics, specifically an elective course for upper-level undergraduates. He's looking for some suggestions of special topics:
The course it titled "Applications of quantum mechanics", and is covering the second half of the text by David Griffiths, whose textbooks I find to be uniformly excellent. A more accurate description of the material would be approximation methods for solving the Schrodinger equation. Not uncommonly in the physics curriculum, when the math becomes more demanding the physics tends to…
pontiff | January 8, 2009I'd never seen this quote from Richard Feynman on the measurement problem:
When you start out to measure the property of one (or more) atom, say, you get for example, a spot on a photographic plate which you then interpret. But such a spot is really only more atoms & so in looking at the spot you are again measuring the properties of atoms, only now it is more atoms. What can we expect to end with if we say we can't see many things about one atom precisely, what in fact can we see? Proposal,
Only those properties of a single atom can be measured which can be correlated (with finite…
drorzel | January 8, 2009In the "uncomfortable questions" comment thread, Thony C. suggests:
You say you're teaching "modern physics" so how about a running commentary on the stuff your teaching?
That's a good suggestion, and I'll start posting some sketchy reports soon. First, though, Bora asks:
What is un-modern physics?
Roughly speaking, physics gets divided into "Classical Physics" and "Modern Physics," with the dividing line coming right around 1900.
"Classical Physics" basically covers fields that were well established before 1900: Newtonian Dynamics, Electricity and Magnetism, most of Thermodynamics, most of…
drorzel | January 8, 2009My senior thesis student this year came to my office today to ask a question as he's starting to work on writing his thesis. I've given him copies of the theses of the last couple of students to work in my lab, and asked him to start on a draft of the background sections. He was worried that he wouldn't be able to make the background sections sufficiently distinct from the corresponding sections in the earlier theses.
This is a sort of tricky point when it comes to issues of academic honesty in science. Scientific questions always have definite right and wrong answers, and that limits the…
rallain | January 7, 2009I saw this video posted on Physics and Physicists:
It reminded me that I had at one point tried to analyze this. I had actually posted something about this on the first generation of my blog (which no longer exists). I have found the analysis, and here it is from the archives. Thanks ZZ for reminding me.
Could this be true, or is it fake? I started to do an analysis of the trajectory, but I found the following frames:
Look at the guy's back. His back starts moving before the water bottle rockets. It must be some type of cable pulling him. If the rockets were propelling him, the rockets…
pontiff | January 7, 2009Special relativity holds a special (*ahem*) place in most physicist's physicists' hearts. I myself fondly remember learning special relativity from the first edition of Taylor and Wheeler's Spacetime Physics obtained from my local county library (this edition seemed a lot less annoying than the later edition I used at Caltech.) One of the fun things I remember calculating when I learned this stuff was what "right in front of your nose" meant in different frames of reference.
Suppose you've got your own handy dandy inertial frame all set up. You've got your rules and you're your clocks and…
rallain | January 5, 2009I finally saw the movie WALL-E. Good flick, I liked it. There was, however, one part I must comment on. You know I can't help myself. I feel like the shark Bruce in Finding Nemo. I try not to attack, but there is a tiny drop of blood in the water. Here is the scene that I want to talk about:
I guess I should give a spoiler alert. Although, I will not talk about the plot of the movie.
In this scene, WALL-E is hitching a ride on this space craft. The space craft is entering a hanger deck of a space station. While the hanger door is still open, WALL-E is clearly hanging on so that he…
drorzel | January 5, 2009It's NFL playoff time, which means that sports fans will be treated to the sight of the most high-stakes farce in sports, namely the ritual of "bringing out the chains" to determine whether a team has gained enough yards for a first down. We've all seen this: the play is whistled dead, a referee un-stacks the pile of players, picks up the ball, and puts it down more or less where the player was stopped. Then he tosses the ball into the middle of the field, to a second referee, who tries to replicate the spot closer to the center of the field. Then a guy on the sideline carrying a big stick (…
rallain | January 3, 2009I finally saw the movie Iron Man. It was good. I feel that I am qualified to evaluate the movie. When I was in high school, I was totally into comic books. Mostly Spider-man, but I still have a significant collection of Iron Man comics. Ok, now you know I am not an Iron Man attacker. I will now attack the movie. Sorry, it's what I do (remember, I already said I liked it). There are several things I could comment on, in fact I recall some other blog talking about the physics of Iron Man.
My attack will center on the scene where Tony Stark (Iron Man) escapes from captivity with his home…
grrlscientist | January 1, 2009tags: life cycle of a star, astronomy, physics, education, streaming video
The average star 'lives' for roughly 12 billion years. This wonderful video provides us with a visual glimpse into the entire life cycle of a G-type star, like our sun, from birth to death [6:29]
rallain | December 30, 2008Just to be clear, Newton probably didn't have a portable video camera. I do. I have one of these Flip Mino pocket cameras. Very nice. You can put it in your pocket. However, there is a problem with cameras like these (think of video from camera phones). The problem is the mass, it is too small.
Video from a camera phone or small portable camera looks too jerky (unless you are careful). Sometimes it is jerky to the point that it makes me feel barfy. The reason this happens is that with a small mass, a force can cause a significant acceleration. Let me draw a picture (you know I like…