One-wheeled wonder.

Perched atop his one-wheeled cycle, Kris Holm zigzags across the treacherous terrain of Mount Seymour in Vancouver, Canada. Sporting a helmet and protective pads, he rolls along the mountain's narrow rock ledges--constantly adjusting his body to keep from falling.

Perilous stunts like this one are nothing new for Holm. This expert unicyclist regularly glides along thin railings like the one that lines a 200-foot-high bridge in Hawaii. He has even ridden his unicycle atop the Great Wall of China.

While Holm may look like a daredevil, he doesn't leave much to chance. Holm is a geomorphologist, or scientist who studies landslides. So he applies his knowledge of various terrains to seek out what he calls "the most rideable path." He avoids loose, rocky terrain that might cause him to wipe out. His knowledge of balanced and unbalanced forces also comes in handy--helping him to rise to the top of his sport.

UNICYCLING 101

Holm says that balancing in place on his unicycle can be just as difficult as riding it across the most challenging terrain. To keep from falling off the cycle, Holm has to pay close attention to his center of gravity--the spot where most of the mass of his body is concentrated.

"For humans, your center of gravity is near your hips," says Holm. To prevent wobbling on top of the unicycle, riders have to keep their hips centered above the wheel. Holm calls this, "keeping your core balanced." When two forces are balanced, they are pushing against each other with equal strength. In this case, one force is the force of gravity pushing down on Holm and the other force is the ground pushing up on him.

But what about when he's looking for a little more excitement? To propel himself ahead, Holm pedals forward and leans slightly frontward. This makes the forces somewhat unbalanced, allowing him to move straight ahead. "You may not notice, but when you are walking you lean a little bit forward," says Holm. The same principle applies to riding a unicycle.

FANCY MOVES

As Holm races down a mountainside, he has to be on the lookout for potential pitfalls and react swiftly to avoid them. There are no handlebars on a unicycle to help with steering. So if Holm spots an obstacle, he has to steer by adjusting his weight. He shifts his weight by moving his shoulders and arms in the same direction he wants to turn.

Only advanced unicyclists should attempt such challenging maneuvers, stresses Holm. Years of experience enable him to naturally shift his weight to steer or to keep from falling. If he feels himself tipping over, he quickly adjusts his core balance in the direction opposite of the way he is falling and he swings his arms out to the side. "It looks kind of funny, but it works!" says Holm.

web extra

Check out www.krisholm.com to view photos of Holm and to see the gear he uses.

BALANCING ACT

1 QUICK INSTINCTS: Holm senses that he is about to fall to his right side. To counter that force, he swings his upper body to the left.

2 SHIFT SIDES: When Holm feels he is falling to his left side, he swings his body to the right.

3 BODY BALANCE: Holm keeps his hips centered above the wheel to stay balanced on his unicycle.

HUMAN SPRING

1 GREAT POTENTIAL: Holm crouches forward, compacting his body. This creates potential energy, or stored energy.

2 BOING! Holm stretches out his body, using kinetic energy, or the energy of motion, to spring himself upward.

3 SAFE LANDING: Holm makes his landing--another successful trick!

PRE-READING PROMPTS

Jump-start your lesson with these pre-reading questions:

* The 2006 North American Unicycling Championships and Convention event was held this past June in Memphis, Tennessee. The event included races, an off-road competition, and a trials event, in which competitors had to navigate obstacles, How do unicyclists use their bodies to maneuver their vehicles during races? How would a unicyclist move his or her body to jump over an obstacle?

* Kris Holm was inspired to start unicyling at the age of 11, when he witnessed a street performer in his home city of Vancouver, Canada, playing a violin while sitting atop a unicycle. What key forces would this street performer need to counter in order to stay balanced on the unicycle?

CRITICAL THINKING:

* Have students pick a sport besides unicycling that involves balance. As a class, discuss the different forces that an athlete would need to counter in order to stay balanced. For instance, which forces push against the athlete and how would he or she adjust the body to balance the forces?

CROSS-CURRICULAR CONNECTIONS:

LANGUAGE ARTS: Extreme unicycling is just one of a growing number of unusual sports. For example, participants of the unusual but true sport of extreme ironing go to treacherous locations, such as a mountain peak, to iron clothing. Have each student imagine a new extreme sport. Then have him or her create a rulebook for the original sport. Be sure to include a description of the equipment used for the sport, as well as safety guidelines. (Caution: Stress to students that this is an exercise in creativity and writing. Participation in the imagined sport is not encouraged.)

RESOURCES

* To learn more about unicyling and to find out about related events, visit: www.unicycling.org

* For a booklet that explains the basics of unicycle riding, read: Ride the Unicycle--a Crash Course!, by Gregg Vivolo, Gregg J Vivolo Publisher, March 2006.

* Learn about bicycle physics at: http://howthingswork.virginia.edu/bicycles.html

* If you plan to use a real unicycle to help you demonstrate some of the forces covered in the article, be sure to check out the safety tips at: www.teachcircus.com/unicycle.html

* For a kid-friendly Web site on unicycling, visit: www.kidzworld.com/site/p6102.htm

Name:--

One-Wheeled Wonder

DIRECTIONS: Fill in the blanks to complete the following sentences.

1. Unicyclist Kris Holm is also a--, a scientist who studies landslides.

2. To keep balance on his unicycle, Holm pays close attention to his --, the spot where most of the mass of the body is concentrated.

3. Holm steers his unicycle by adjusting his arms and shoulders to shift his--

4. When Holm crouches forward, he compacts his body. This creates--, or stored energy.

5. To jump, Holm stretches out his compacted body. Using--, or energy of motion, he springs himself upward.

ANSWERS

1. geomorphologist

2. center of gravity

3. weight

4. potential energy

5. kinetic energy