Tuesday, April 22, 2008

Measure Your Car's Drag Coefficient!

You know you're a true physics geek (that's a good thing) when even a trip to the Quickie Mart is an opportunity to do a physics experiment.

It's still better when the experiment tells you whether those bangin' new fender skirts on your Honda CRX and the monster wing you bolted on are holding you back in your own private version of The Fast and the Furious 4. Or, even worse these days, burning a hole in your gas card.

Click the pic to check out an Instructable that tells you how to measure your car's drag coefficient.

A low drag coefficient is crucial for both high fuel efficiency and high speed cruising. It's also very hard to calculate for anything other than a really simple shape. So experiment is the way to go.

If anyone out there has a Scion xB, I'd love to know what sorts of measurements you get in real life driving. It can't be good. On the bright side, the slower you go, the less the drag affects your mileage -- and xB's look best when they're slow cruising.

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Wednesday, April 16, 2008

Spirit of Saint Louis

Hi, I'm Gabe Popkin. I'm new to the Physics Buzz, but not to physics. I got an undergraduate degree in physics from Wesleyan University in 2003 and now I work in the APS Education Department, mostly on a project to help physics faculty recruit and prepare future teachers. I am also involved in creating educational materials based on cutting-edge science research.

I just got back from the APS April Meeting in Saint Louis, where I spent much of my time manning a booth for an APS-led project called the Physics Teacher Education Coalition, or PTEC. PTEC is a group of around 110 universities, colleges, and one national lab at which at least one faculty member has taken an interest in working with some of tomorrow's physics teachers. The Coalition began in May of 2003 as an outgrowth of the PhysTEC project, which funds a smaller number of universities to develop strong teacher preparation programs that can serve as national models.

So you may imagine it can be a hard sell to get physicists to talk about teachers at a research-driven event like the April Meeting. Indeed, one guy, when I asked him whether he was interested in what APS does in education and outreach, flatly said "Not at all," and hobbled off. Others were perhaps more respectful, if no less apathetic. But the truth is, many if not most physicists are concerned about the state of physics education in America's schools, and rightly so. The world and the workplace are becoming more technical every day, and there is plenty of evidence suggesting that many of our country's students are not getting the preparation they need to keep up. And so APS has made it a top priority to engage its members in preparing the next generation of physics teachers, who will in turn prepare the next generation of physicists.

Here is Assistant Director of Education Monica Plisch talking to a meeting attendee about teacher preparation.

Of course I was able to get away from the booth for a little while to catch some of the other action. Probably the most interesting talk I heard was Burt Richter's presentation of some of the findings of the upcoming APS Panel on Public Affairs' report on energy efficiency. Did you know that if you take the integral over the cost to society of all the CO2-saving technologies we can implement right now, it comes out to just about zero? Yep, this plot of carbon savings versus cost from McKinsey and Company shows the carbon savings of various technologies versus cost. So there is nothing economic stopping us from taking these steps; politics may be another story, though. The total potential savings is over 3 gigatons of CO2 per year. I have no intuition for a gigaton of carbon dioxide, but currently we emit 7.2 gigatons/year, so 3 is significant, especially considering projected growth of 2.5 gigatons/year by 2030. I also found it interesting that the most costly carbon-saving innovation - car hybridization - seems to be among the most popular. Is this perhaps because your car makes a very clear public statement about your commitment to saving the world that you just don't get from, say, promoting coal mine methane capture?

Of course you can't visit Saint Louis without marveling at the gigantic inverted catenary curve that stands by the river, and just a few minutes' walk from our hotel. I became slightly obsessed with this shape, and searched the internet for proof that the catenary is the most beautiful curve. At least I hoped to find a poll similar to those that have identified Euler's identity as the most beautiful theorem in mathematics. But no such poll has been conducted, so I will simply assert it without proof, and leave it to the neurobiologists to find the region of the brain that releases happy chemicals when it sees the catenary, or the golden spiral, or any of those other famously pleasing forms.

The catenary is the shape that minimizes the potential energy of a hanging chain, and when inverted and used to form an arch, it gives a structure that is subject to no shearing forces, only compression. I thought surely if an inanimate thing like a chain could assume this curve without the slightest intelligence, I, with my mighty human brain, should be able to calculate it. But the solution is surprisingly nontrivial, and my calculus of variations being rusty, I defer the proof until a later date. Suffice it to say that I secured a piece of paper from the unamused receptionist in the visitor center that informed me that

y = -127.7 ft * cosh(x/127.7 ft) +757.7 ft.

where x = 0 is at the center of the arch. Naturally.

Being at the base of such a large geometrical form is disorienting in a way that is both unexpected and pretty cool. It also makes for interesting photo opportunities, and I leave you with a few pictures I took from various positions. For a more whimsical take on the arch's mathematics and history, I encourage you to read this post from Cocktail Party Physics.

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Fun with Acoustics: Wine Bottles, an RC Car, and the Mario Brothers Theme Song

After seeing this video, I think I need to start collecting wine bottles (I don't know what I'm going to do with all that wine, though).

These folks from somewhere in China set up the bottles - precisely spaced and partially filled with fluid to tune them to various musical notes. All this effort went into an elaborate way to play the theme from the Mario Brothers video game when the bottles were hit by the small hammer attached to a passing remotely controlled race car.

Mario Theme Played with RC Car and Bottles - Watch more free videos
And to think I'm wasting my time working when I could be doing way cool stuff like this.

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Tuesday, April 15, 2008

Inside Nature's Time Capsule

I couldn’t resist a science news story that’s so reminiscent of Jurassic Park. Amber is the closest thing to a natural time capsule I can think of. It’s almost a time machine. The stuff preserves bugs, leaves, feathers, and who knows what else almost perfectly for millions of years. Researchers recently found a few hundred new species of fossilized animals that had been trapped in amber since the Mesozoic Era. And, with a 3D printer, they can make complete models of the fossilized creatures.

The mosquito-containing amber atop John Hammond’s cane in Jurassic Park was transparent – giving a lovely little image of the bug trapped inside. But a large percentage of amber turns opaque as it solidifies, so it’s impossible to see the animals trapped inside it. Bring on the physics! To look inside these bits of amber, the paleontologists are using a technique known as propagation phase contrast microradiography (phew!).

Physicists have found that if you want to look inside something that visible light won’t pass through (like granite or opaque amber), you could always try looking through it with a different kind of light. In this case, the amber is penetrated with X-rays created by a synchrotron.

A synchrotron is a particle accelerator that uses both electric and magnetic fields to gradually accelerate particles around a circular track. To be accelerated, the particles must be charged; but charged particles that accelerate emit light (a property that is present in many facets of your everyday life). Electrons in a synchrotron can be accelerated so that they emit steady streams of X-rays. The X-rays penetrate the amber and give an image of what lies inside.

In a second study, the researchers found prehistoric feathers that may have belonged to a dinosaur (ok, they can't prove that...yet...but it is a legitimate theory!).

The process is still relatively slow. It takes about four days to analyze ten kilograms of amber. Developments are being made to increase that amount by ten. Because so much of fossilized amber is opaque, the scientists are eager to start looking at the history stuck inside.

Above: Chunks o' amber




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Wednesday, April 02, 2008

Self Cleaning Clothes - What to Wear This Summer?

Whether you're extremely environmentally conscious or just plain lazy, self-cleaning clothes are a good thing for everyone. Except those of us that gain comfort and confidence from the intense sanitizing power of the traditional washer-dryer. No one can tell me I don't smell pine fresh if I know my clothes have just gone through the wash cycle. Self cleaning clothes leave things a bit more debatable; but it is true that self-cleaning material would benefit energy guzzling humans in more than one way.

Researchers announced in a February 2008 issue of the journal Chemistry of Materials that they have now found a way to coat wool with nanoparticles of titanium dioxide, making the fabrics essentially self-cleaning. The technology was developed in 2004, but could only be bound to cotton. Next on the way will hopefully be silk and hemp.

This particular type of self cleaning is achieved by leaving the fabrics in the sun. The titanium dioxide is a photocatalyst - so exposure to UV light causes it to burn organic materials, like food and bacteria. The burning occurs at room temperature, so no damage comes to the wearer or the material. In fact, the researchers say the particles may actually make the materials stronger, so they last longer when they are washed traditionally.

The images represent wool with three different degrees of saturation in the nanoparticles. The bottom three images shows the wool fully coated and modified to be self-cleaning, with a red wine stain initially (left), after 8 hours (center) and 20 hours (right). The top is without nanoparticles, and the middle is with nanoparticles unmodified.

The key question remaining is how the titanium oxide burns organic materials like food and wine, but not organic materials like wool, cotton, or skin. Any ideas would be great.

Because of the anti-bacterial nature of the newly coated fabrics, it's likely that the self cleaners will first make their way into hospitals. But I imagine there will be difficulty trying to convince the health board that hospital workers should not wash their clothes. Assuming they still wash the hospital wear, that kind of defeats the enviro-friendly aspect of the clothes. However, it it might make a difference in stopping the spread of bacteria in hospitals.

LiveScience reported in January 2007 that killing bacteria was the driving force behind another self cleaning method, now used by soldiers to protect against bacterial infections. The Air Force developers went straight for the gut when the created underwear that doesn't need washing. Serious consumer marketers should probably consider ties first.

Apparently the Air Force's approach is working well. Jeff Owens, one of the researchers who developed the technique said "During Desert Storm, most casualties were from bacterial infections-not accidents or friendly fire. We treated underwear for soldiers who tested them for several weeks and found they remained hygienic. They also helped clear up some skin complaints."

The article doesn't specifically mention how this particular method is achieved. What it does say is that nanoparticles are attached to the fabric using microwaves. Then bacteria-, dirt-, and oil-repelling chemicals are bound to the nanoparticles. What chemicals they use, or exactly how they then make the material self-cleaning is left to be guessed. Other reports said the technology would be introduced into sports wear, but I haven’t heard anything about it since.

But wait! It gets weirder! Rather than eradicating your clothes of bacteria, how about implanting them with it? Researchers have experimented with planting a harmless strain of E. coli in clothing fibers, giving the bacteria the chance to feed on whatever falls on the clothes. Right now, they're still figuring out whether or not the bacteria could survive on the irregular diet, and how long it would take them to clean up an average stain, and how they are ever going to market this to anyone. I shouldn't judge - as the researchers point out, we are actually crawling with microorganisms and bacteria even after a shower and an old-school clothes wash. As long as I couldn't feel the shirt moving, I suppose I'd give it a try. Then again - there's always the slight possibility than an underfed shirt could start to feed off of its wearer.

But one often overlooked aspect of our daily energy consumption is in the water and heat used by the washer and dryer. You can buy more ecologically friendly washers and dryers, but there's also the waste product to consider. Suds from most types of detergent don't mesh well with natural ecosystems. So maybe self-cleaning clothes represent a step into the future - and particularly, a future where technology actually leads to lower energy consumption.


1 - Courtesy of New Scientist:

2- Self-Cleaning Keratins
Walid A. Daoud, S. K. Leung, W. S. Tung, J. H. Xin, K. Cheuk, and K. Qi
Chem. Mater.; 2008; 20(4) pp 1242 - 1244;

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