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SCIENCE OF SPORTS: Spring Man

Hugh Herr's sneakers put springs in a runner's stride. By storing potential energy in springs and making muscle power more effective, his sneakers could revolutionize many sports. Herr, who lost his legs in a mountain-climbing accident, is convinced these sneakers -- and his other ingenious devices -- will help people make the most of their natural abilities. Join Herr in field tests of his spring shoes and other inventions.

Notes & Discussion
Activity: Energy on the Move
Report From the Field: Hugh Herr, Engineer and Spring Shoe Inventor

 BIOLOGY/LIFE SCIENCE muscles PHYSICAL EDUCATION running PHYSICAL SCIENCE kinetic energy,potential energy TECHNOLOGY energy storage,materials

NOTES & DISCUSSION
• Energy comes in many forms -- kinetic (motion), heat, light, sound, chemical, electrical and nuclear. When energy is used to make things move, it is transformed from one form into another. All energy transformations can be traced back to the sun -- the original source of energy for life on earth.

• Some energy transformations are as simple as what occurs when sunlight warms a person's face and changes to heat energy. Some energy transformations take place in complex chains. When a battery-operated toy car is put in motion, chemical energy (stored in battery) changes to electrical energy (released from battery), which changes to kinetic energy (wheels turn) and sound energy (noise).

• As you saw on Frontiers, Hugh Herr's inventions attempt to maximize the use of muscle energy. How do his sneakers do this? (They make use of the muscle energy that in conventional sneakers would be transformed into unusable heat energy.)

ACTIVITY: ENERGY ON THE MOVE

Investigate the transformation of muscle energy to heat energy by trying these activities at four work stations. Then record your observations.

STATION #1

MATERIALS
• thick rubber bands

PROCEDURE
1. Hold a rubber band to your upper lip to sense its temperature.

2. Remove the rubber band, stretch it rapidly, then hold it to your upper lip while it is still stretched.

OBSERVATIONS
• Describe the feeling on your lip after the rubber band was stretched.

• Identify the energy transformations that occurred.

STATION #2

MATERIALS
• "Superball" with hole drilled in it
• thermometer

PROCEDURE
1. Carefully place the bulb end of the thermometer in the ball and record the temperature.

2. Remove the thermometer and bounce the ball for 5 minutes; take turns in your group.

3. After the 5 minutes, insert the thermometer in the ball again and record the temperature.

OBSERVATIONS
• Temperature of the ball before bouncing.

• Temperature of the ball after bouncing.

• Identify the energy transformations that occurred.

STATION #3

MATERIALS
• hammer
• nails
• blocks of hard wood

PROCEDURE
1. Pound a nail 4 to 5 cm into the wood block.

2. Pull the nail out with the claw of the hammer and touch the nail.

OBSERVATIONS
• Describe the feeling after touching the nail just removed from the block.

• Identify the energy transformations that occurred.

STATION #4

MATERIALS
• plastic bottle with screw-on top
• thermometer
• fine sand

PROCEDURE
1. Fill the plastic bottle half full of sand.

2. Carefully insert the bulb of the thermometer into the sand, wait 2 minutes, then record the temperature.

3. Remove the thermometer, screw on the cap, and vigorously shake the bottle for 5 minutes.

4. Remove the cap from the bottle, carefully insert the thermometer in the sand, and then record the temperature.

OBSERVATIONS
• Initial temperature of the sand.

• Final temperature of the sand.

• Identify the energy transformations that occurred.

• Although you were able to feel or measure some of the heat energy produced in the exercises above, you could not feel or measure all of it. Think of where the "unfeelable" or "unmeasurable" heat energy could be in each activity.

• The law of conservation of energy tells us that energy cannot be created or destroyed. It can only be transformed from one form to another. Try to identify all the energy transformations that occur when you operate a hair dryer.

SOLUTIONS
1. The rubber band feels warm because the molecules slide over each other, creating heat from friction when it is stretched. (fusion in sun) nuclear --> (photosynthesis) light --> chemical --> (digestion) chemical --> (nervous) electrical --> muscle --> kinetic --> (friction) heat. Some of the heat energy from the rubber band will cause the air molecules around it to move faster.

2. Each time the ball strikes the floor, most of the kinetic energy from its fall is used to make the ball almost return to the height from which it was dropped. When the ball strikes the floor, molecules in the superball collide, and some of their kinetic energy changes to heat energy, raising the temperature of the floor, and to sound energy when it strikes the floor. (starting with muscle) muscle--> (before release) potential--> (after release) kinetic --> (friction/contact with floor) heat/sound.

3. The nail feels warm because some of the energy used to overcome the force of friction between the nail and the wood changed to heat energy. (starting with muscle) muscle--> (hammer) kinetic --> (nail) kinetic --> (friction) heat. Some of the heat energy will increase the temperature of the hammer and the block of wood.

4. The temperature of the sand increases because the particles are rubbing against each other and their kinetic energy is being changed to heat energy because of friction. (starting with muscle) muscle --> heat. The temperature of the plastic bottle also increases.

LAB NOTES
• You can use this activity to show how kinetic energy changes into heat energy and to demonstrate the law of conservation of energy.
Note: you may wish to set up materials at each work station ahead of time.

CREDIT: Tim Yanka, science teacher at Holicong Middle School in Buckingham, PA, contributed this activity.

REPORT FROM THE FIELD: HUGH HERR, ENGINEER AND SPRING SHOE INVENTOR

On this episode of Frontiers, we meet Hugh Herr, the creator of innovative running shoes that may one day add spring to every athlete's steps. How did Herr begin his career as an inventor? He explains, "I was having a lot of pain with my artificial legs and needed to improve the prosthetic socket, the interface between the artificial and human leg. I knew I needed more engineering background, so I switched from computer science to physics and then went to MIT to study mechanical engineering."

Herr was still a graduate student when he came up with the idea for spring shoes. His experience demonstrates that a great idea is only the first of many steps involved in bringing an invention to the marketplace. "Our original prototype used spring steel that weighed a ton. But we tested it anyway, and I could tell the idea was good." Most shoemakers didn't believe Herr's idea would be a success and told him to come back when he had a polished prototype. He spent about \$30,000 on broken shoes in a sometimes discouraging search for a carbon composite.

When can we expect to see spring shoes in the stores? Says Herr, "If the manufacturers I'm meeting with make a quick decision, maybe they'll be ready to test market a few hundred thousand shoes in early 1995. They wouldn't be widely available for a couple of years after that."

What's it like to be an inventor? "I think 24 hours a day -- even in my sleep, and I often wake up with the answer I'm looking for," says Herr. "I also have about 15 projects going at once. That's what it takes to be a successful inventor because the chances of an idea falling through are pretty high." Herr's work has also led to another insight. "When you're working to develop a project, you realize that it's amazing that anything ever works at all! You sure gain a lot of respect for complex projects like the Space Shuttle!"

 Scientific American Frontiers Fall 1990 to Spring 2000 Sponsored by GTE Corporation, now a part of Verizon Communications Inc.