A grand prix racing motorcycle is many things: most impressively, a marvel of
engineering that costs hundreds of thousands of dollars to develop and
build, and one of the fastest machines on wheels, capable of speeds in
excess of 210 miles per hour and able to retain a grip on the road at lean
angles of 60 degrees or more.
But looked at scientifically, a racing bike is nothing less than a kinetic demonstration
of the laws of physics. Freddie Spencer, a legendary grand prix champion of the eighties
and now "dean" of Freddie Spencer's High Performance Riding School in Las Vegas, puts it this way: "Motorcycle racing is a real-world physics lab where the penalty for wrong answers is a lot more dramatic than a bad grade."
The rider shifts weight into the turn to help the motorcycle change direction and lower its center of gravity.
2. Kinetic Energy:
At speed on a straightaway, a motorcycle’s energy is directed forward.
3. First Law of Motion:
Newton stated that a body in motion persists in a straight line unless compelled to change.
Slowing the motorcycle from high speed for tight turns causes heat buildup in its brakes and can diminish effectiveness.
5. Centrifugal Force:
In fast turns, lean angle and forward motion counteract the powerful pull toward the outer edge of the track.
A special compound in these rounded tires allows traction on asphalt even at lean angles of 60 degrees and more. Credit: Fiat Yamaha Team
According to Charles Falco, the University of Arizona's chair of condensed-matter
physics and co-curator of the Guggenheim Museum's The Art of the Motorcycle exhibition, the initial physics lesson to be learned watching a racing bike hurtle into a tight turn
is Newton's first law of motion: "Every object persists in its state of rest or uniform
motion in a straight line unless it is compelled to change that state by forces
impressed on it," explains Falco. To a rider, this means that the faster a motorcycle is
going, the less it wants to turn.
Converting a bike's kinetic energy from straight ahead to turning requires a negotiation
with physics in a couple of ways. First, a rider pushes the handlebars slightly away
from the direction of the turn. Because the wheels act as gyroscopes, this countersteering
leans the bike in the opposite direction (into the turn), which puts the tires at an angle,
narrowing what engineers call the contact patch and making the bike easier to turn.
At the same time, the rider moves off the bike in the direction of the turn. The
lean angle of the motorcycle shifts the center of gravity to the side, causing the bike
to turn, while the weight redistribution lets the machine stay slightly more upright.
At the point of maximum lean required to get through a turn at the highest possible
speed, centrifugal force wants to pull the bike machine off the track, and the rider
uses traction, gravity, and momentum to stay in the game.
To explain why the machine moves at all, Falco invokes Newton's second law of motion:
A force applied to an object will cause it to accelerate. "This will happen until the rider runs
out of track, or other forces become nonnegligible, such as wind resistance," says Falco.
On some tracks, grand prix motorcycles approaching tight turns must slow from
more than 200 mph to around 40 mph. Friction on the brakes (primarily the front
brakes) makes this possible. "All that excess energy has to be dissipated by the brakes
in the form of heat," Falco says, thus bringing up the law of conservation of matter
and energy. Some of this heat is transferred to the hydraulic-brake fluid, which can
cause brakes to lose stopping power, with potentially disastrous consequences.
Engineers use space age ceramic materials to avoid this problem, and riders become
skilled at getting on and off the brakes quickly.
Successful race riding is a lot like paying taxes: You want to push the rules as far
as you can without breaking them. There is a very fine line between optimum cornering
and crashing, where outward, downward, and forward forces balance precisely.
But rules are rules. "Speaking on behalf of physicists everywhere," Falco declares,
"nothing that ever happens on a motorcycle breaks the laws of physics. In fact, motorcycles
are excellent examples of just how well physics works."
Physics, Fun? Oh, Yes!
Physics is fun for physicists, but some students, to say the least, don't immediately warm to the subject. A good way to overcome resistance is to show students the direct role physics plays in their lives and interests, and the rich resources on the Internet makes doing so easy. Here, to get you started, is a selection of Web sites and videos guaranteed to bring physics to your classroom in ways that will be both fun and fascinating.
How to Throw a Curveball
This short, straightforward tutorial, "Thrown for a Curve," comes from the Exploratorium, San Francisco's splendid self-described "museum of science, art, and human perception." It even suggests how to make such activity classroom safe (almost): "We've found that it's much easier to throw these pitches and observe the results by throwing a Styrofoam ball."
To create the interactive training Web site Fugu.com's concise, 105-second How to Throw a Curveball video, the site teamed up with Marc McDonnell, from AllStar Dugout, a baseball and softball instructional facility. McDonnell so clearly explains the throwing technique that even a physicist can master it.
The free online how-to video library ViewDo.com's How to Throw a Curveball is a good, clear curveball demonstration. Watch for the slow-motion sequence at the end, which enables students to closely observe the ball's unique behavior.
"How to Throw a Curveball," from eHow.com, features excellent four-step text instructions, a "Tips & Warnings" section, and readers' comments to make this pitching lesson the perfect complement to Fugu.com's and ViewDo.com's offerings.
The Physics of Skateboarding
The Exploratorium's nicely presented "Skateboard Science" Web feature focuses on motion and forces, and how they relate to skateboarding. This easy-to-navigate site includes video, a glossary, equipment details, and even some skateboarding history.
"The Physics of Skateboarding" is a thorough teacher-developed lesson plan ("based on material from the Exploratorium") that guides students in learning skateboard stunts and relating them to Newton's three laws, gravity, momentum, trajectory projectiles, circular motion, and friction. Includes several links to relevant text, pictures, and videos.
An engaging activity on another page called "The Physics of Skateboarding" was developed by a graduate student at the University of North Carolina at Wilmington as part of that state's 2001 Standard Course of Study for 8th Grade Science.
This guide to TeacherVision's "Skateboard Slosh" demonstration, designed for grades 3-6, directs you and your students as you attach a container of water to a skateboard and observe how movement and force affect the liquid.
Owen Edwards is a contributing editor for Edutopia and Smithsonian magazines.