Show Number 910

# HIGH JUMP

How do high jumpers set new records?

David learns how physics helps high jumpers break records.

• Would you like to be able to jump higher?
• How do you feel when you figure out ways to improve your performance?
• What are the benefits of combining science with sports?

Discussion

The jump style called the "Fosbury Flop" dramatically revolutionized the high jump. Dick Fosbury's movement technique involves racing toward the bar in a curved approach, lifting off with the left foot, pivoting the right leg backwards and sailing over the bar backwards, stretching the back and flipping the legs upward. In 1968, Fosbury set a personal and Olympic record of seven feet and four inches - a full two and a half inches higher than the 964 Olympic record. By 1980, 13 of the 16 Olympic high jump finalists used the Fosbury Flop.

All three phases of the high jump require allowing for and using different physical forces. The approach involves accelerating the body along a curved path that leads up to the bar. At that point, the jumper is actually leaning away from the bar, allowing for the centrifugal force that will pull him or her into a vertical position for the jump.

The lift-off requires the jumper to overcome gravity by launching directly upwards while pushing against the ground. The greater the force applied to the ground, the greater the force that returns to the jumper.

Bar clearance requires careful management of the human center of gravity. The center of gravity is that point where an object balances perfectly. The force of gravity pulls down vertically and is concentrated at each object's center of gravity. For an object to remain balanced, the center of gravity must be on a vertical line with the point of suspension, above or below it. The ideal high jump position involves draping the body over the height of the crossbar at the peak of the jump.

### Things to Talk About

1. How would you practice balancing your center of gravity? Why do you need to go over the bar backwards? How does the center of gravity affect different animals when they are jumping?
2. In the 'Newton's Apple' segment on the high jump, Tom Ecker said that the high jumper's center of gravity always follows a parabola. Is it the same for a ball, a pen or a shoe? Why or why not?

Gravity--The force that tends to pull any two objects together. The force of gravity is usually large enough to be noticed only when one of the objects is massive, such as the earth.

Center of Gravity--The point at the center of an object's weight distribution where the force of gravity acts.

Balance--Stability produced by even distribution of weight on each side of the vertical axis.

Mass--The amount of matter an object has.

Weight--The force of gravity pulling on an object's mass.

Parabola--The mathematical curve that describes the flight of any thrown or tossed object (e.g., a jumper, a cannonball, or a ball).

### Resources

• Chase, Sara B. Moving to Win: The Physics of Sports. New York: Julian Messner, 1977.
• Ecker, Thomas. Basic Track and Field Biomechanics. Mt. View, California: Tasnews Press, 1985.
• Laws, Kenneth. The Physics of Dance. New York: Schirmer Books, 1984.

#### Additional Sources of Information

• Trainers from Local Fitness Centers
• School Coaches
• Sports Clinics or Doctors

# Activity Page

Get Pushy!

Experiment with biomechanics to improve the height of your jump.

Main Activity

You can jump higher, too. Experiment with different positions, styles and techniques to find ways to jump higher.

Materials:

• 2-3 feet of butcher paper
• Colored chalk
• Tape

1. Tape the paper up on the wall so it is about two feet above the jumper's head.

2. Take turns standing with the right shoulder perpendicular to the sheets of paper. Hold a piece of chalk in your hand.

3. Jump from a standing position and mark the paper with the chalk at the high point of your jump.

4. Experiment with different jumping styles to see if you can jump higher.

Suggestions:

• Start your jump from a squat position, with your arms above your head.
• Start your jump from a squat position, using your arms to pump.
• Start your jump from a standing position, then squat, then jump.
• Take a running start then jump.
• Try your own style, using combinations of the above suggestions, or using your own jumping techniques.

5. Record the success of the different styles you tried.

Questions

1. What ways can athletes combine their knowledge of physical forces to improve their performances? What ways can technology be used in this kind of research?

2. Why is the curved approach used in high jumping? Are there any other track events that use it?

3. How can high jumpers get the best use of their leg muscles? How could they add more power to the lift-off?

4. Find out what the "stretch reflex mechanism" is. How is this helpful to jumpers? Is it helpful in any other sports?

Bend over and pick up something from the floor. Describe how your center of gravity changes. Stand against the wall. Without letting your feet or buttocks move away from the wall, try to pick something up. What happens?

Observe other sports that use physical forces. Look at pictures or films of sporting events. Can you find the athlete's center of gravity in the pictures or in the freeze frame shots of the film? Invite a karate instructor to your class and ask him to discuss the "physics of karate". How do karate experts combine their centers of gravity with momentum?

Go to a basketball game and watch how the players lift-off and use their center of gravity for balance. Talk with the coach and ask how players can improve their styles by consolidating physical forces in one direction. What happens if the players are blocked by the other team when jumping up with the ball? How are forces used during free shots?

Try some experiments with the balance beam in the gym. Take some friends and try balancing on the beam. Discuss what is involved during a balancing act. Try balancing by holding a pole horizontally in front of you. Does this affect how you stay on the beam? What happens if you use a shorter pole? A longer pole? How do tightrope walkers use their center of gravity when performing feats on the wire?

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