Physics Buzz: How to Build a Spectrometer with Just Three Household Items
How to build a cereal box spectrometer.
Monthly Archives: August 2009
Driving Cognitive Costs Down
Realizations of Rounded Rectangles
Time for an expert: I asked Professor Jürg Nänni, author of the exemplary Visual Perception, a book detailing our best-to-date scientific understanding of the processes involved in visual cognition. “Could rounded rectangles actually take less effort to see?”
Nänni confirmed my theory: “You are absolutely right. A rectangle with sharp edges takes indeed a little bit more cognitive visible effort than for example an ellipse of the same size. Our “fovea-eye” is even faster in recording a circle. Edges involve additional neuronal image tools. The process is therefore slowed down.”
IT’S PROBABLY ONE REASON WHY ALLCAPS is so frikkin’ annoying, too.
Getting All Charged Up
I bought another toy recently. A “fun fly stick,” which is a static electricity generator. Here are two of my colleagues playing with it. The levitating object is some aluminized mylar, i.e. tinsel.
The low ceiling in my office makes it difficult to truly appreciate it, but does show some physics. You can see the tinsel collapse when it touches the ceiling and discharges, and then pop open again when it’s free. The charges on the aluminum repel each other, and spread out as much as they can in order to minimize their energy. That’s what we are taught in E&M, and it’s easy to see this with a deformable object rather than the canonical rigid sphere.
The tinsel does actually get charged (rather than having some induced charge distribution), which you can feel on the occasions where you get too close and it attacks your face. Not too much of a shock, though. I tried aluminum foil, but it’s too heavy. (foil = fail) Packing peanuts didn’t repel like I expected, but that may work better in drier weather. The tinsel targets are a bit delicate and I have empirical evidence that they do not stand up to the treatment of two/three year-olds.
This is an ad from ThinkGeek (not where I got this particular toy) that uses a little more free space.
Think Ahead
Does closing roads cut delays?
Yes, because people do the wrong analysis.
The authors give a simple example of how this could play out: Imagine two routes to a destination, a short but narrow bridge and a longer but wider highway. Let’s also imagine that the combined travel times of all the drivers is shortest if half take the bridge and half take the highway. But because each driver is selfishly trying to seek the shortest route for himself, this doesn’t happen. At first, everyone will go for the bridge because it’s shorter. But then, as the bridge becomes backed up, more drivers start taking the highway, until the congestion on the bridge starts to clear up. At that point more drivers go back to the bridge, which then becomes backed up again. Eventually, the traffic flow settles into what’s called the Nash equilibrium (named for the beautifully minded mathematician), in which each route takes the same amount of time. But in this equilibrium the travel time is actually longer than the average time it would take if half of the drivers took each route.
Note that this still happens even if – indeed, especially if – all the drivers have perfect information about what all the other drivers are doing, such as with a GPS that gives real-time traffic updates.
The problem here is similar to the one of feedback, as anyone who has designed and tested gain/feedback circuitry can attest. There is an oscillation to the signal — an ebb and flow of traffic density. There is a delay in the time between the signal and the feedback, and at some point the delay is 180º out of phase, so you add to the problem rather than subtracting from it.
Note that the last quoted sentence is actually incorrect — the real-time traffic update information tells you where traffic is, not where it is going. If you knew that a lot of drivers were heading to the bridge and would be there in 15 minutes — about when you would arrive — you wouldn’t take the bridge. But all you know is how many are on the bridge right now. The information you are missing is how many drivers have made the decision to use the bridge.
Taking a Whizzo
Making a Crunchy Frog. But if we took the bones out…
Or, how to avoid prosecution for not saying, “crunchy raw unboned real dead frog.”
Since gummy frogs normally come boneless, you’ll have to add them back in manually. It’s a dirty job, but somebody’s got to do it. Conventional confections employ nuts, puffed rice, wafers, or corn flakes for crunch, but these are no ordinary confections: we use Pop Rocks.
Cash for Thermodynamic Clunkers
Refrigerator Recycling Programs Take Off
The recent flurry of new programs in New England stems in part from the recent introducton of the Regional Greenhouse Gas Initiative, a Northeastern program that caps greenhouse gas emissions in an effort to combat climate change, as well as from energy efficiency initiatives in individual states, according to Mr. Sirkin.
Utilities commonly estimate that homeowners can save up to $150 a year on their electricity bill by dumping their old refrigerator or freezer. Old refrigerators, made prior to 1990, also use three times as much electricity as new ones, the utilities say. In addition, refrigerators made before the mid-1990s may also emit ozone-depleting chlorofluorocarbons.
Nice Car, John Bigboote
Use more honey. Find out a-what she knows.
This is Not a Step
Schneier on Security: Risk Intuition
“We have to make people understand the [security] risks,” he said.
It seems to me that his co-workers understand the risks better than he does. They know what the real risks are at work, and that they all revolve around not getting the job done. Those risks are real and tangible, and employees feel them all the time. The risks of not following security procedures are much less real. Maybe the employee will get caught, but probably not. And even if he does get caught, the penalties aren’t serious.
Brahe had a Sponsor. Kepler Works.
The bottom plot is the same thing but zoomed in to see more detail. That second dip is a lot more obvious. It’s not another planet blocking starlight, which is what you might first guess. It’s actually the light from the planet being blocked by the star!
The planet is reflecting light from the star, just like the Moon reflects sunlight, allowing us to see it. When the planet passes behind the star, we don’t see that light anymore, so the total light from the system drops a wee bit. It’s not much, and totally impossible to see from the ground, but Kepler was able to spot it. And that’s critical, because it turns out this dip is about the same thing we’d expect to see if a planet the size of the Earth were to pass in front of the star. In other words, the drop in light from a giant planet going behind its star is about the same as we’d expect from a smaller planet passing in front of the star.
The fact that Kepler spied this dip at all means that, if somewhere out there an Earthlike world is orbiting a star, Kepler will be able to detect it!
Incredible.
This is pretty cool.
Someone Divided By Zero
flickr: Maelstrom #3 -Kauai, Hawaii
This awesome photo is from the Mokolea Lava Pools, after a wave had hit and the water was draining. The post title is one of the comments. There’s a still-quite-cool “before” picture, too.