Physics
drorzel | August 19, 2010At the tail end of Tuesday's post about wind and temperature, I asked a "vaguely related fun bonus question:"
If the air molecules that surround us are moving at 500 m/s anyway, why isn't the speed of sound more like 500 m/s than 300 m/s?
This is another one that people are sometimes surprised by. The answer is simply that in a sound wave, the air molecules don't really go anywhere. When something creates a sound-- say a foolish dog barking at a perfectly harmless jogger going by outside, to choose an example completely at random-- there isn't any actual thing that travels from the noisy dog…
drorzel | August 18, 2010Most of the time, when we talk about seeing quantum effects from light, we talk about extremely weak beams-- looking at intensities where one photon more or less represents a significant change in the intensity of the light. Last week, though, Physics Buzz wrote up a paper that goes in the other direction: they suggest a limit on the maximum strength of a laser pulse due to quantum effects, specifically the creation of particle-antiparticle pairs.
This is a little unusual, in that most of the time when people talk about really intense lasers, they end up discussing them as an oscillating…
rallain | August 17, 2010Let me start with the video. Here is a guy flying a plane in a barrel roll and pouring some tea at the same time. Talk about multitasking.
How can he pour upside down? Well, there are two ways to look at this. First, I can look at this in the frame of the plane. For this case, I can invoke the fake force - centrifugal force. Oh yes, I am going to do it. You probably remember all your physics instructors warning you to never ever do this. Well, they say that because they are afraid you will do something bad with it. Here, I will only use the centrifugal force for good.
What is the…
elerner | August 17, 2010While the superstar of the particle physics world, the Large Hadron Collider, gets all of the attention (and the glamor shots), there's plenty of interesting science that can be done on the atomic level within an otherwise ordinary laboratory on the campus of an update New York university. Consider, for instance,the lab of Uncertain Principles' Chad Orzel, who has recently taken his readers on a four-part tour of his scientific specialty: making atoms extra cold. While the LHC sends protons whizzing through miles of underground beam pipes in order to more spectacularly crash them together,…
rallain | August 17, 2010I see that Doug at Nanoscale Views has fond memories of the hit show The Mechanical Universe. If you have never seen this show, it is quite excellent (even if old).
Perhaps the best thing about The Mechanical Universe is that it might be the best that traditional lecturing can provide. Oh, I know it isn't quite the same. Students can't ask questions while watching a video. But the main point is that if you want to go with some type of traditional lecture style format for a class, you would be hard pressed to do better than this. Or maybe something similar - there are other good video…
drorzel | August 17, 2010I got forwarded a physics question last night asking about the connection between wind and temperature, which I'll paraphrase as:
Temperature is related to the motion of the atoms and molecules making a substance up, with faster motion corresponding to higher temperature. So why does it feel warmer when the air is still and why does wind make you feel cold?
This is a moderately common point of confusion, so while I responded to the question in email, I'll also appropriate it for a post topic. So, why doesn't "windy" equal "hot," given that wind consists of moving air molecules?
The full…
rallain | August 16, 2010I can't let it go. There is more here to explore. First, I can't believe that I looked at braking and then turning but not turning then braking. And what about braking while turning? I will model braking and then turning - but it won't stop here.
Consider a few motions. I could turn and then brake (which I am looking in this post). Another option would be to brake and then turn. I already showed that this takes a longer distance than just stopping. Braking and then turning in general won't work. Suppose I brake and slow down to a certain speed. Now I am a certain distance away from…
drorzel | August 16, 2010Last week's series of posts on the hardware needed for laser cooling and trapping experiments dealt specifically with laser-cooling type experiments. It's possible, though, to make cold atoms without using laser cooling, using a number of techniques I described in two posts back in January. Those didn't go into the hardware required, though, so what's different about those techniques in terms of the gear?
Less than you might think. In fact, most of the labs that do these experiments use exactly the same sorts of equipment that laser coolers do. Including some lasers.
It's not all of them, but…
drorzel | August 15, 2010A couple of new-to-me but good physics blogs to point out this week:
All That Matters by Joerg Heber. This looks like it will be updated weekly-ish, and has a couple of good entries, including a nice write-up of an ultrafast laser experiment that I had flagged to write about before I got distracted by crazy people and lab porn this week.
The Dayside by charles Day of Physics Today. This has roughly daily updates, on a wide range of stuff.
Both of these cover physics beyond the default particle-physics-and-cosmology that you can find in dozens of places, and Day even has a post titled Why I…
rallain | August 13, 2010You know I have trouble letting stuff go, right? I am still thinking about these crazy long basketball shots. Here are some more thoughts.
Really, there are two things I am interested in. First, commenter Scott Post suggests that the drag coefficient might be around 0.25 instead of 0.5. I don't know. For the discussion before, it doesn't really matter. My point was to see a numerical model for a falling ball would be similar to the time and distance from the video. Changing the drag coefficient to 0.25 gives values that are still close to the video. So, I still think the video is real…
drorzel | August 13, 2010The third category in our look at lab apparatus, after vacuum hardware and lasers and optics is the huge collection of electronic gear that we use to control the experiments. I'll borrow the sales term "test and measurement" as a catch-all description, though this is really broader than what you'll usually find in that category.
This category covers all sorts of stuff, from power supplies to data acquisition equipment, but we'll start with the oscilloscopes.
The picture above shows two of the many oscilloscopes that rattle around my lab. These are used for almost everything that involves a…
drorzel | August 13, 2010Some folks I used to work with at NIST have looked at cheap green laser pointers, and found a potential danger. Some of the dimmer-looking green lasers are not so dim in the infrared, and in one case emitted 10X the rated power in invisible light. This could be a potential eye hazard.
You can read their full report on the arxiv. It's got a nice description of how green laser pointers turn infrared light into visible light, which is really pretty awesome-- a guy I met at a conference once declared them the coolest invention ever, because it's "quantum optics in the palm of your hand." Better…
rallain | August 12, 2010There is something I am working on that will need some type of angle sensor. I am going to use a potentiometer. First, who came up with that name? Isn't this name the same as a voltmeter? Something is wrong with that name. How about we just call it a variable resistor or something like that?
These things are pretty easy to find if you have some old electronic stuff. Here is one I found in our "junk room".
This one was used in a lab as a variable resistor with plugs built in. The normal potentiometer has three connections; one for each end and one for the variable position in the…
drorzel | August 12, 2010The problem with writing about fake physics is that once you start, it's hard to stop. And there's always something new and disreputable to find, such as this hideous bit of scammery. As I said in How to Teach Physics to Your Dog, if quantum physics really allowed you to amass vast wealth just by wanting it, Dave Wineland's publications wouldn't need to acknowledge funding from a handful of acronyms-- he'd be able to bankroll his own research out of his personal fortune..
Quantum physics is not magic. It allows many things that seem weird and counterintuitive, but those effects are very…
drorzel | August 12, 2010Following on yesterday's discussion of the vacuum hardware needed for cooling atoms, let's talk about the other main component of the apparatus: the optical system. The primary technique used for making cold atoms is laser cooling, and I'm sure it will come as no surprise that this requires lasers, and where there are lasers, there must also be optics.
There are lots of different types of lasers used for laser cooling experiments, but they all need to have certain properties: tunability, stability, and adequate power. Tunability is important because laser cooling requires light at exactly…
rallain | August 12, 2010There is this commercial that has been coming on lately showing some people reading the Kindle at the beach. Why is this a selling point? It has to do with the way the Kindle works compared to something like the iPad. I would take a picture, but I have neither of these devices. Instead, I will make a diagram.
Maybe you can't tell from my diagram, but I am using the black rays to represent light reflected from the Kindle and red rays to represent light produced from the iPad. And that is the key. The Kindle does not have a light source, it is very similar to a piece of paper. The iPad…
rallain | August 12, 2010This summer I taught the part II of algebra-based physics. It is odd, but I rarely teach this course. I usually end up teaching the calculus-based version (with Matter and Interactions). There is something strange. If you look at the algebra-based physics I and calculus-based physics I, they are just about the same course. Both essentially cover forces, momentum, energy, and angular momentum. Oh, I know - some also cover waves and pressure and sound and stuff.
I think what tipped me off to the big difference in the algebra-based physics II is the theme in Matter and Interactions. Yes,…
drorzel | August 11, 2010Over in the reader request thread, Richard asks for experimental details:
I'd be interested in (probably a series) of posts on how people practically actually do cold atoms experiments because I don't really know.
I needed to take some new publicity photos of the lab anyway, so this is a good excuse to bust out some image-heavy posts-- lab porn, if you will. There are a lot of different components that go into making a cold-atom experiment, so we'll break this down by subsystems, starting with the most photogenic of them, the vacuum system:
(Click on that for a much bigger version.)
This…
drorzel | August 11, 2010A Japanese physicist who I worked with as a post-doc spotted the Japanese edition of How to Teach Physics to Your Dog in the wild, and picked up a copy. He sent along a scan of a couple of pages of the text, one of which I reproduce here:
I had totally forgotten that Japanese books are often printed with the text in vertical columns from right to left, which creates a slightly weird effect. What's even stranger, though, is the way the equations are done-- they're also rotated to be vertical, but the kanji characters are rotated as well. Not that the rotation changes the readability in any…
drorzel | August 10, 2010A reader emails to ask about a new-to-me theory of physics, called "Quantum Space Theory" being promoted by a fellow named Thad Roberts. I wouldn't usually bother with this, but Roberts was one of the speakers at TEDx Boulder. this is disappointing, to put it mildly-- TED is a respected organization, and I don't like seeing them lend their support to something that is just dripping with kook signifiers. The key paragraph of the overview of the theory is:
To start grasping this higher-dimensional intuÂitive picÂture check out the book excerpts in the book excerpts secÂtion. If you are more…