Speed skating: a high-powered machine lets racers rest their legs while they soar on skates.

Engineer Jorg Kahlert zips into a padded leather bodysuit. He straps on a helmet and goggles, dons elbow and knee pads, and pulls gloves onto his hands. Seconds later, the need for serious safety equipment is clear: Rolling on only the small wheels of his in-line skates, Kahlert races around a track at more than 90 kilometers (56 miles) an hour.

Kahlert doesn't rely on Supermanlike legs to reach such breathtaking speeds on skates. Rather, he hitches a ride behind the Latest in extreme sports equipment: the SkootaSkate. This wheeled machine--resembling a cross between a lawn mower and a motorcycle--has a high-powered engine. Kahlert and colleagues created the machine to tow trained and daring skaters to speeds much faster than they could reach themselves.

MUSCLE MIGHT

Normally, to reach top speeds on skates, a person uses pure leg strength--pumping back and forth against the road. "[The skater] exerts a big force on the ground," says Steven Manly, a physicist at the University of Rochester in New York. And according to Newton's third law of motion, the ground pushes back with an equal and opposite force-propelling the skater forward. With each leg pump, the skater's speed increases. But using only these forces, even top in-line skaters can't attain speeds reached with a SkootaSkate.

That's because each backward stroke of the leg requires a skater to perform work, or a force that moves an object through a distance. To do the work, the skater's body converts chemical energy gained from food into mechanical energy, which moves the skater's leg muscles. But the power (see Nuts & Bolts, right), or the rate at which a person can convert that energy, is limited.

POWER SOURCE

To surpass the speed limits set by leg power, the Skootakate propels skaters with engine power. The engine converts gasoline's chemical energy (energy stored in chemical compounds) into mechanical energy to rotate the machine's front wheel and tow the skater. One racing model of SkootaSkate boasts a mighty 2,700 watt (unit of power) engine. Even a top skaters power pales in comparison. "A trained athlete can put out about 400 W of mechanical power for fairly long periods of tune, says Chris Waltham, a physicist at the University of British Columbia in Vancouver, Canada.

SKOOTA STUNTS

With the added power of a SkootaSkate engine, Kahlert and other skilled skaters in Europe are strapping on safety gear to race each other on enclosed tracks at mind-blowing speeds.

Specially trained stunt skaters are also using SkootaSkates to enhance their routines. These skaters can rocket off ramps and perform mid-air flips and spins. "The amount of time they can spend in the air depends, in part, on their speed when they leave the ramp," explains Manly.

To fly sky-high, these skaters need to build an extreme vertical velocity, or speed in one direction. It helps them fight against the force of gravity pulling them back toward Earth. With the extra speed supplied by a SkootaSkate, these trained daredevil skaters can rocket higher off the ramps and pull record-breaking stunts.

Nuts & Bolts

Power is the rate at which energy is converted from one form to another or transferred from one object to another. Consider a high-watt lightbulb: Each second, it converts more electrical energy I to light energy and heat energy J than a bulb with a lower wattage.

1 According to--, the ground pushes back on a skater's legs with an equal and opposite force.

A gravity

B Newton's third law of motion

C power

D Newton's laws of work

2 The SkootaSkate can boost a skater's speed because

A the engine does little work.

B it has less power than the skater's body.

C the engine has a low wattage.

D its engine converts energy at a higher rate than your body can.

3 Gasoline stores

A mechanical energy.

B chemical energy.

C power.

D 400 watts.

4 To jump sky-high off a ramp, a stunt skater tries to maximize

A vertical velocity.

B the force on the ramp.

C gravity.

D friction.

DID YOU KNOW?

* While most of the high-powered engines on SkootaSkates run on gasoline, some models of the machine sport electric engines. The electric engines are much quieter than the fuel-powered ones.

* The SkootaSkate model with the 2,700-watt engine is designed for racing. A lower-power model has an electrical engine that can produce a mere 250 W. With top speeds of approximately 24 kilometers (15 miles) per hour, this model offers skaters a slight boost in speed.

CRITICAL THINKING:

* Besides leg power, what other factors could limit an in-line skater's speed? What types of equipment could help a skater overcome these restrictions, allowing him or her to glide faster?

CROSS-CURRICULAR CONNECTIONS:

MATH: Suppose a 2,700-watt engine can propel a skater to a distance of 1,500 meters in 120 seconds. Use the equation for power to calculate the force in Newtons exerted by the engine. Hint: Power = (Force x Distance)/Time

RESOURCES

* "Flight of the Skootaskater," by Sally Palmer, BBC Focus, January 2005.

* This Web site has clear explanations of forces, work, and power. Includes student activities: www.physics.ucla.edu/ k-6connection/force.wp.htm

* For activities and science project ideas related to energy, see: www.energyquest.ca.gov/projects/

1. b 2. d 3. b 4. a

CHECK FOR UNDERSTANDING

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

1. According to Newton's--law of motion, when a skater pushes his or her leg against the ground, the ground pushes back with an--and--force--propelling the skater forward.

2. Each backward stroke of the leg requires a skater to perform work, or a force applied through a--.To do the work, the skater's body converts--gained from food--which is used to move the skater's leg muscles.

3. The SkootaSkate's engine converts gasoline's--,or energy stored in chemical compounds, into--to rotate the SkootaSkate's front wheel.

4. --is the rate at which energy is converted from one form or another, or transferred from one. And--is a unit of power.

5. To fly sky-high, stunt skaters need to build an extreme vertical--, or speed in one direction. That helps them fight against the force of--pulling them back down toward Earth.