Jearl Walker is the kind of teacher who’d just about lay down his life for his students, and he has the scars to prove it.
“After one lecture, I had to get to the university health service, real fast,” Walker said. “The doctor looked up and said, `Now what have you done to yourself, professor?’ “
In fact, Walker had suffered second-degree burns while giving a demonstration of fire walking in Physics 102. On other campuses, such a course would be described in the catalog as an introduction to the science. But at Cleveland State University, Walker’s course is listed as “The Flying Circus of Physics,” in deference to his unorthodox teaching methods.
Educational purists might ask what fire walking has to do with physics. Walker says he finds it a good way to ensure that college freshmen never forget the Second Law of Thermodynamics.
According to that classic axiom of physics, when a hot object comes into contact with a cooler object, heat inevitably flows from the former to the latter. But it takes time for that energy transfer to be completed-a corollary to the Second Law that Walker counts upon when he brings a trough of burning coals to class.
The secret of fire walking, Walker said, is to step lively and lift the feet high. That way, they are in contact with individual coals only for a fraction of a second, from one step to the next. So not enough heat is transferred to burn the skin, as Walker, 48, has annually explained to students while outlining the basic principles of thermodynamics during the 20 years he has taught Physics 102.
“One time, though, a few coals got stuck in between my toes,” Walker said. “But I beat back the pain and completed a 50-minute lecture before hobbling over to the health service for treatment.”
Indeed, Walker takes a certain macho pride in noting how many times his demonstrations of scientific laws have not gone according to design, to the detriment of his body. A few years back, he was a guest lecturer at Western Illinois University in Macomb. For a finish, he lay on the floor while his teaching assistant used a hammer to break a concrete block sitting atop a board resting on his chest.
The point of the demonstration was to show how a force large enough to do Walker harm, if his body had to absorb it all at once, could be reduced to atolerable level. It would be dissipated through the time it took for the hammer’s blow to break through the block. Then Walker would jump up to explain that automobile airbags work on the same principle, protecting a crash victim by delaying the impact of his head and the windshield.
It was an experiment that Walker and his assistant had done successfully before. This time, though, a fragment of the block hit Walker in the face, cutting him badly.
“I stood up, blood was pouring down my cheeks, and the audience was gasping,” Walker said. “It was the best finale I ever had.”
Facing a sea of indifference
Walker became a stuntman-professor in response to a disheartening discovery that every young teacher makes. In each generation of undergraduates, a few get really turned on by one subject or another. They go on to graduate school, burying their noses in a library or laboratory for years, soaking up knowledge. Finally they become teachers and step up to a podium, excited by the prospect of sharing their learning.
“The very first time I taught a college class and looked out at the expressions on the students’ faces, I got a sinking feeling,” Walker said. “There I was, standing in front of dozens of young people who just didn’t want to be there.”
That kind of classroom standoff, Walker explained, comes from the fact that scholars go through life differently than ordinary folks do. Professors live in a mental universe. The rest of us aren’t really comfortable with abstractions, preferring to measure the world by our own firsthand experiences.
An English professor can sometimes use the power of analogy to bridge that culture gap. When his Shakespeare course bogs down, he can ask members of the class to compare their adolescent heartaches with those of Romeo and Juliet. Similarly, a sociologist can tout his subject as helping students understand their families and communities.
But physics is a different story, as Walker learned while working on his doctoral degree at the University of Maryland and serving an apprenticeship as his professor’s teaching assistant. While handing back some tests, one student looked at her flunking grade and asked, “How come none of this has anything to do with my life?”
“I said, `Well, Sharon, if you give me until next class period, I think I can find some examples of how physics does play a part in your life,’ ” Walker said. “Though I stayed up half the night, I couldn’t come up with a single one.”
The student’s question kept bugging Walker, prompting him to examine some ordinary, everyday situations with a scientist’s eye. Whenever he could explain one on physical principles, he’d put the problem on the blackboard before class started, as a brain teaser for early birds. At a subsequent session, he’d give the answer.
His students thus learned why Rice Krispies go “snap,” “crackle” and “pop”; why tea leaves collect in the center of a cup as you stir it, even though the spoon drives them to the sides; and the force that causes two nearby Cheerios to pull together in a bowl of milk (see accompanying story).
The news spreads
Word got around campus that his students not only didn’t cut class, but came early. Other teaching assistants asked Walker how he pulled off that near miracle. So he began mimeographing his solutions to problems in everyday science for distribution to their classes too.
By the time he had finished graduate school, Walker had accumulated enough material for a paperback book, “The Flying Circus of Physics” (Wiley), which has now been translated into 11 languages.
Impressed with Walker’s knack for getting lay people interested in science, the editors of Scientific American magazine gave him a monthly column, “The Amateur Scientist.” For 13 years he tackled the kinds of problems that puzzle ordinary folks even though scientists usually duck them, only reluctantly giving up the column in 1990 when he was asked to prepare a new edition of a leading college textbook in physics.
For Scientific American’s readers, Walker analyzed such issues as “Does convection or Bernoulli’s principle make the shower curtain flutter inward?” He devoted a number of columns to topics in kitchen-table science, such as, “The physics and chemistry of a failed bearnaise.”
At Cleveland State, Walker found himself assigned to large lecture halls, instead of the smaller rooms he had worked in as a teaching assistant, and he realized he’d have to do more than scribble a few puzzles on the board to engage his students’ interest. It struck Walker that his new professorial stage looked more like a theater than a classroom, prompting him to think that maybe a few dramatic devices could put some life into his teaching method. For a first experiment, he asked a campus carpenter to build two beds of nails, the kind Hindu holy men supposedly use.
His students quickly realized they hadn’t registered for just another straight-out-of-the-textbook course the day Walker took off his shirt and lay down on one of the beds. An assistant covered him with the other one, its nails making contact with his bare chest. Walker invited a student to stand atop the resulting sandwich of himself and the two beds of nails. When he asked her to jump up and down, her classmates shuddered, imagining all those sharp points being driven into their professor.
“Actually, it’s the fact that there are so many nails that saves my skin,” Walker said. “If there were only a few, they’d go right into me. But with dozens and dozens, the force of the student’s weight is spread out, thus reducing the proportion of force at the tip of each nail to the point where it’s too little to puncture me. Sideshow performers explain the bed-of-nails trick as mind over matter. In fact, it’s just a bit of simple physics.”
Walker brought a container of molten lead to a subsequent lecture. He put a thermometer in it, which registered 700 degrees. Wetting his fingers, he momentarily plunged them into the hot liquid too. He explained to his students that, flashing into steam, the water on his skin had formed a protective, if short-lived, glove.
With the success of those demonstrations, Walker caught the performer’s bug, and he began appearing in costume when appropriate. For his lecture on relativity, he dons a fuzzy wig and old sweatshirt and affects Albert Einstein’s German accent. When explaining sound transmission, he ducks out in mid-lecture, changing into a skirt and sweater in a nearby closet. Reappearing as a cheerleader, he puts a megaphone to his lips and demonstrates how that simple mechanical device magnifies the carrying power of the human voice.
“Out of the classroom, I’m rather shy; at parties I go sit in a corner,” Walker said. “The only precedent for my physics performances was in Sunday school as a kid. I got bored with our teacher, Chuck, and his simple-minded presentations. So I started posing theological problems, which he and I would debate, which greatly increased attendance. Soon half the kids in the neighborhood were showing up to see the Chuck and Jearl show.”
As word of Walker’s classroom style spread, he began getting invitations to demonstrate his methods off-campus. On several occasions he has been summoned to court to explain the physics of car accidents to juries hearing personal-injury suits. In 1987, an NBC talent scout heard about Cleveland’s oddball professor, and Walker was invited to be on “The Tonight Show.”
Johnny Carson, a science buff, kept Walker in front of the cameras for 20 minutes, scrubbing a standup comic scheduled as the next act. Walker showed Carson the old standard magician’s trick of pulling a tablecloth off, leaving the plates and dishes standing on the bare table. The secret, Walker explained, is to get the tablecloth moving very fast, thus reducing the friction between the cloth and the plates, which would otherwise cause them to follow the cloth off the table.
“I also showed Carson how to make a spoon stick to the forehead, by breathing lightly on it,” Walker said. “Moisture from your breath acts as an adhesive, but you can’t have too much, otherwise the various layers of liquid slide by each other and the spoon falls. What you want is a thin covering of moisture, one molecule thick.”
The nitrogen trick had to go
Walker has also been asked to demonstrate his teaching methods at meetings of professional scientists. As a result, a few other physics professors have taken to livening up their lectures with theatrical devices from Walker’s bag of tricks. But he proudly notes that his road-show imitators usually borrow his less dangerous stunts.
Still, he confesses that even he sometimes has to set a demonstration aside for the sake of longer life. One of his standard routines used to be drinking liquid nitrogen, at minus 328 degrees, taking care to hold it in his mouth, not swallow it. Then he would blow a most impressive plume of nitrogen gas over the podium and 3 feet into the audience.
The bit depended upon the outer layer of nitrogen boiling to form a gaseous buffer between the colder liquid and his mouth. One time, though, it didn’t work according to formula, and he left the lecture hall with a terrible, ringing sensation in his mouth.
“My dentist took a look,” Walker recalled, “and said: `Do us both a favor and drop that lecture from your syllabus. You’ve cracked the enamel on two teeth.’ “.
If a Rice Krispie falls in a forest …
Professor Jearl Walker’s introduction to the physics of everyday life:
If two Cheerios are placed near each other in a bowl of milk, they will move toward each other. Why?
Capillary action causes milk to rise between two nearby Cheerios. The surface tension of the milk attracts objects to it. In this case, the surface tension of that little bulge of milk pulls the two nearby pieces of cereal together.
When you stir a cup of tea, the leaves wind up at the center of the bottom. Why? It would seem that the centrifugal action of the spoon should force the leaves toward the side of the cup.
The spoon’s motion does set up a centrifugal force that pushes the tea leaves toward the side of the cup. They don’t stay there, though, because the pressure of that centrifugal force is stronger at the top of the cup than along the bottom because of friction between the bottom layer of water and the cup. That pressure difference causes water to be drawn up from the bottom of the cup to the top along the central axis. When the water reaches the top of the cup, it flows toward the side, then down to the bottom, and along the bottom to the center. At the side of the cup, the stream picks up the tea leaves and carries them along until the point where it begins to rise again, at the cup’s center. There gravity takes over, the leaves fall out of the rising stream and are deposited at the center, bottom of the cup.
Why do Rice Krispies go “snap,” “crackle” and “pop”?
Air is trapped in the cereal during manufacture. Milk weakens the walls of the cereal particles and they rupture, releasing the air with a popping sound.
