Speed 101: Motorcycle Racing as Real-World Physics Lab | Edutopia
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WHAT WORKS IN EDUCATION The George Lucas Educational Foundation

Speed 101: Motorcycle Racing as Real-World Physics Lab

Isaac Newton hops aboard a two-wheeled teaching tool.
Owen Edwards
Related Tags: Project-Based Learning

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."

1. Gravity:

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.

4. Thermodynamics:

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.

6. Friction:

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."

Owen Edwards is a contributing editor for Edutopia and Smithsonian magazines.

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Anonymous's picture
Anonymous (not verified)

There is no "Centrifugal Force" with respect to a motorcycle cornering on a racetrack. It is an apparent (i.e fictitious) force. This apparent "force" is not a force at all. Why would an education publication print something like this at all? It is simply perpetuating a science misconception that physics teachers everywhere are trying to undo!

life-long learner's picture
Anonymous (not verified)

Can you be more explicit? I'm intrigued by your statement that a ficticious force "is not a force at all."

From wikipedia (http://en.wikipedia.org/wiki/Fictitious_force):

"A fictitious force, also called a pseudo force[1] or d'Alembert force[2], is an apparent force that acts on all masses in a non-inertial frame of reference such as a rotating reference frame. The force F does not arise from any physical interaction, but rather from the acceleration a of the non-inertial reference frame itself. Due to Newton's second law F = ma, fictitious forces are always proportional to the mass m being acted upon."

What misconception is being perpetuated?

Mark Nichol, Edutopia.org Web Production Editor's picture
Anonymous (not verified)

According to Charles Falco, the physicist interviewed for this article, "Centrifugal ('center-fleeing') force is something students are taught in their first physics class is an incorrect concept. Yes, it's true that the force is centripetal ('center seeking'). However, the fact that you are thrown off the merry-go-round toward the outside, not toward the center, makes the name counterintuitive, and if I were to say 'centrifugal force' at a physics conference, I guarantee that everyone there would understand exactly what I meant."

Anonymous's picture
Anonymous (not verified)

Mark you are not thrown outward from a merry go round !!!!!. If you let go you will continue in a straight line just lie Newton's 1st law predicts. I would say that centrifugal force is counter intuitive. If the froce acts straight out from the center then that is the direc tion you woould accelerate and you don't. Centrifugal force does not exsist!

bcknblk's picture
Anonymous (not verified)

in regards to motorcycles, can you put into laymen terms why a wider handle bar steers easier and explain the advantages of a lower center of gravity? Thanks.

GeoffonTour's picture
Anonymous (not verified)

I recently had a discussion with someone about whether or not a bike has more grip at a higher corner speed. I argued that it did not, but he said something about the bike's lean angle making it dig in more if you went faster.

I'm fairly sure the effect would be negligable but he was adamant it wasn't.

Anonymous's picture
Anonymous (not verified)

Longer handlebars make a longer lever to move around the pivot point. In this case the steering stem. It is the same as using a breaker bar to "gain" more power to remove a stuck bolt. As you increase the distance from the steering head with a longer handlebar you increase your ability to generate a force that turns the wheel. Hope this helps.

Anonymous's picture
Anonymous (not verified)

I am not opposed to anyone, students included, using wikipedia for some things, but citing it as a reference is not one of them.

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