You can use Valentine's Day chocolate and your microwave to perform sophisticated physics calculations! All images: Kathy Ceceri

If you’re a long-time reader, you may remember the great leftover Easter Peeps microwave experiment. Well, today we’re going to be nuking leftover Valentine’s Day chocolate to demonstrate one of the constants of physics, the speed of light. Chocolate makes a very appropriate medium, because the heating property of microwaves was first discovered by a scientist whose candy bar melted in his pocket when he got too close to a microwave device being tested for use in radar.

WARNING: This experiment may take several tries to get right. We are not responsible for any weight gained. To avoid familial strife, be sure to only do this experiment with your own chocolates or with candy which you have been authorized to access. You can probably find some leftover boxes on sale this week.

The demonstration works because microwave ovens produce standing waves — waves that move “up” and “down” in place, instead of rolling forward like waves in the ocean. Microwave radiation falls into the radio section of the electromagnetic spectrum. Most ovens produce waves with a frequency of 2,450 megahertz (millions of cycles per second). The oven is designed to be just the right size to cause the microwaves to reflect off the walls so that the peaks and valleys line up perfectly, creating “hot spots” (actually, lines of heat).

What you do with the candy is to find the hot spots and measure the distance between them. From that information, you can determine the wavelength. And when you multiply the wavelength by the frequency, you get the speed! Here’s what you do:

1. Make sure the candy is in a microwave-proof box. Better yet, take the chocolate out and put in a microwave safe dish.
2. Remove the turntable in your oven. (You want the candy to stay still while you heat it.) Put an upside-down plate over the turning-thingy, and place your dish of candy on top.
3. Heat on high about 20 seconds.
4. Take the chocolate out and look for hot spots. Depending on the candy you use, you may have to feel the candy to see where it has softened. With the cherry cordials we used, we saw several shiny spots and one place where the chocolate shell melted through, releasing the sweet syrup inside.
5. Measure the distance between two adjacent spots. This should be the distance between the peak and the valley (crest and trough) of the wave. Since the wavelength is the distance between two crests, multiply by 2. Finally, multiply that result by the frequency expressed in hertz or 2,450,000,000 (2.45 X 10⁹ for my son who is just learning scientific notation).

In our trial, we measured a distance of roughly 6 centimeters. 6 x 2 x 2,450,000,000 = 29,400,000,000 centimeters per second, or 294,000,000 meters per second. This is awfully close to 299,792,458 meters per second, which is the speed of light. Not bad for some leftover chocolate and a kitchen appliance!

I discovered this experiment at Null Hypothesis, although it can be found all over the Internet, including many versions with fancy charts and animations. By the way, melted chocolate bars are perfect as ice cream topping. Just saying.

Kathy Ceceri also blogs at Home Physics.

Physics teacher Luther F. Davis III will try to bike 140 virtual miles in his classroom Thursday to raise money for diabetes

Luther F. Davis III, a physics teacher at Lake Mary High School in Florida, likes to give his students memorable lessons. He has smashed cinder blocks over his chest while lying on a bed of nails to illustrate pressure and had students drag him around the football field with ropes to show how forces direct motion — and won the Presidential Award for Excellence in Science and Mathematics Education in the process.

On Thursday Davis will be trying a new kind of demonstration: he will spend the entire teaching day — 7 hours — pedaling his bicycle on rollers. The purpose is to give his students a visual lesson in work, power, energy, angular momentum, torque, and other topics. You can view a Powerpoint show at his website, Cycling Physics. And while Davis is pedaling, he’ll have his students streaming his bike ride/physics lesson live from the classroom and take questions via online chat.

All this is part of Davis’ training for the upcoming “Tour de Cure” 100-mile bicycle ride in Orlando to benefit the American Diabetes Association, which he plans to ride on February 28th. (He’s collecting donations via PayPal on his website).

Davis, who switched to cycling from marathon running only a few months ago, and has already ridden 128 miles across the state, likes the idea of using real-life examples in his teaching.

“I’m trying to think outside the box,” he said by phone from his home in central Florida. “I decided to include some of my ‘creative classroom antics.’”

He has an ongoing “Family Physics” series of activities, like sending his students home after a lesson in acoustics to build drinking-straw horns with their parents. (He’s also started introducing his own kids, ages 2 and 5, to the physics of cycling whenever they wander out into the garage to see Daddy riding on his indoor trainer.) During the event he’ll be involving students in helping him with hydration and nutrition — making sure his system of tubes to deliver water and energy drink are working, and feeding him banana chips and peanut butter and jelly sandwiches as needed. Students will also be responsible for the running  the webcast, recording data and answering questions from other students and the Internet.

“Sometimes the less you teach the more the students get out of it,” he said.

Davis also had some learning to do with setting up his classroom environment. He’ll be riding on rollers that let both wheels spin freely — and which he set on skateboard wheels so that the whole frame can move back and forth about 8 inches, giving him more freedom to get out of the saddle and hammer. (One of the hardest parts of riding on rollers, he noted, is having to pedal constantly in order to maintain the angular momentum that keeps the bike upright.) And along with his homebuilt hydration system, he’ll also be using several fans to provide wind resistance and keep cool.

Although he’s a little nervous about how the whole enterprise will work, he’s also very excited.

“This is something I’m not going to let fail,” he said. “I feel well-prepared. It’s going to be an exciting experience for me, my students, and anyone else who pays attention.”

Luther Davis’ Cycling Physics classroom event to benefit the American Diabetes Association can be seen from 7:25 am to 2:25 pm (EST) on Thursday Feb 4th.

Kathy Ceceri also blogs at Home Physics.

Instant Egghead Guide: Physics

You’ve gotta love a book that follows “Chapter One: Matter” with “Chapter Two: Quantum Theory.” The Instant Egghead Guide: Physics by Brian Clegg and Scientific American does just that, and then continues on through chapters about Light, Relativity, Forces and Energy. The cover calls it “60-Second Science,” and each subject is a two-page spread that takes about a minute or two to read. The chapter about matter, for instance, is broken down into subjects such as atomic structure, various phases of matter, string theory and the big bang.

Each subject has three short sections: The Basics, On the Frontier, and Cocktail Party Tidbits. The Basics is just that: a very simple, straightforward explanation of the topic at hand. On the Frontier is usually a little extra information, sometimes but not always about the current state of knowledge on a subject, or perhaps an example of how this bit of information is used in practical applications. Cocktail Party Tidbits is the fun stuff: little trivia about Einstein or a snarky remark Feynman once made.

My main complaint: the book tends to shy away from using formulas, probably to make things more accessible for the “Math is hard!” contingent, but I ran into this sentence which I had trouble parsing until I realized they were using the parentheses as in math, rather than as in English:

As mechanical work is the force applied times the distance moved, and power is work divided by time, then power is also force times (distance over time)—that is, force times velocity.

(The other potential source of confusion is spelling out “times” in a formula which also includes “time.”) I don’t know if avoiding mathematical notation really does anyone any favors or just muddles things a bit. Fortunately, this sort of thing didn’t occur too often but this particular case stood out for me.

Also, I think this is the first time I’ve read an entire physics book without a single diagram in it, which is a shame. I think a few well-constructed diagrams would have gone a long way toward making some key concepts easier to understand and remember.

Those of you who are physics geeks most likely won’t learn anything new from this book (except some nifty trivia that will come in handy next time you’re at a cocktail party, whatever that is). But if you need a refresher course—if, say, your high schooler starts asking you about things you haven’t studied since you were in high school—this is a handy book to have around.  With a little over 100 topics, you can spend just a few minutes a day and get a pretty good overview of physics in a short period of time. At the very least, it’ll help you get a few more of the jokes on The Big Bang Theory.

The Instant Egghead Guide: Physics is available from Amazon or other fine booksellers.

Wired: A broad overview of physics in bite-sized, easy-to-swallow chunks.

Tired: Some diagrams and mathematical formulas would have been nice.

Note: St. Martin’s Press provided a review copy of the book for GeekDad.

Newton uses a prism to demonstrate that white light can be broken down into a spectrum of colors. In Lego. Credit: Kubik-Rubik

Today is Sir Isaac Newton’s birthday, as you know if you’ve been on Google’s homepage. In addition to laying out the Laws of Motion, he also did innovative work on the properties of light, as can be seen in this Lego re-enactment. I’ll be reviewing a new kids’ book about Newton — who was quite an interesting and somewhat quirky guy — very soon.

Kathy Ceceri also blogs at Home Physics.

Sports are less of a drag when they're tied in with physics. "The Science of the Olympic Winter Games" is produced by NBC and the National Science Foundation.

How do free-style skiers manage to twist their bodies while flying through the air? What’s it feel like going into a curve inside a speeding bobsled? If the thrill of victory and the agony of defeat isn’t enough to convince your progeny to join you on the couch for the Olympic Game telecast this winter, you might want to try enticing them with some extreme sports science.

In preparation for the 2010 Olympic Games from Vancouver, Canada, NBC and the National Science Foundation have teamed up to produce  “The Science of the Olympic Winter Games“, a series of 16 short (4-minute) videos on the physics behind a hockey player’s slapshot and a figure skater’s spin. Using a Phantom Cam high-speed camera to capture images at rates of up to 1,500 frames per second, the series turns usually fast-paced sports coverage into a Matrix-like freeze-frame sequence.

To help explain what’s happening in these amazing shots of top athletes and state-of-the-art sports equipment caught in mid-flight, the series includes commentary from experts like Ithaca College exercise and sports science professor Deborah King and Melissa Hines, director of the Cornell University Center for Materials Research. Kids (and adults) without much science background will find that Newton’s Three Laws of Motion, the Law of Conservation of Angular Momentum and other scientific concepts are much easier to understand when they’re illustrated with real-life footage.

And who knows? “Olympic Science” might even get some sports fans interested in physics!

For more kid-friendly physics resources, check out Kathy Ceceri’s new Home Physics blog.