Under pressure: how does the amount of air inside a football affect its performance? One teen kicks his way to an answer.
According to legend, the west-coast team tried just about everything to keep its archrival running in circles: Some say that the Raiders coated their palms with a gluey substance known as "stickum." That way, they could catch the ball easier than their yellow-and-black-clad opponents could. The California team may have also slathered its jerseys with a slippery goop, so they'd be hard to grip in a tackle. Rumor even has it that the Raiders let air out of the football when it was the Steelers' turn to kick a field goal.
Dan wondered about that last trick: Would a ball with less air have deflated his home team's chances of scoring a field goal? Determined to find out, Dan decided to make this question the focus of his seventh-grade science fair project.
To kick off his project, Dan performed research to find out what forces act on a football during play. Based on the information that he gathered, he developed a hypothesis, or a possible answer to a scientific question. Like any good hypothesis, Dan's was testable:
There is an ideal air pressure for footballs. When a football is inflated or deflated beyond that ideal amount, it will not travel as far when it is kicked.
Before Dan could design an experiment to test his hypothesis, he had to tackle a construction project. The teen knew he couldn't kick a football with the same amount of force every time. That would be a problem for a science experiment: "With an inconsistent kick, your data wouldn't be correct, and you wouldn't prove anything," Dan explains.
So with help from his dad, Dan built a kicking machine. By winding the machine's "leg" and then releasing it, Dan could maintain a consistent kick throughout his experiment.
With the kicking machine ready, Dan crafted a detailed procedure, or list of steps, for his experiment. And it was a winner: Dan nabbed a first-place award in a regional division of the Pennsylvania Junior Academy of Science's annual science fair. Read on to see how Dan's easy-to-follow steps led to success.
* What materials do you need for your experiment?
Make a detailed list. Be sure to include amounts and measurements.
* Define your control, or standard against which you will compare your results. Dan measured the distance the ball traveled when it was inflated with the manufacturer's recommended level of air pressure: 85 kilopascals (12 pounds per square inch). Air pressure is the force of air's outward push on a container--in this case the football--divided by the area of the walls of the container.
* Identify your independent variable, or the factor that you change during your experiment. Dan's independent variable is the amount of air pressure that the football has.
* Determine your dependent variable, or the factor that responds to the change in the independent variable. In Dan's experiment, the dependent variable is the distance the football travels when it is kicked.
* Keep all other variables constant. The independent variable should be the only factor that changes during your experiment. During Dan's testing, outside temperature, humidity, and wind could have affected the football's air pressure or the distance the ball traveled. To keep these variables constant, Dan performed all of his kicks--or trials to his experiment--on the same day.
* Repeat the experiment.
Conduct several trials. If you get similar results among the trials, your conclusions will be more reliable. Dan kicked the football six times at each air pressure.
LIST OF MATERIALS
** Weather report
** Kicking machine *
** Flat, open field
** Measuring tape
** Pro-size football
** Air pump
** Air pressure gauge
** Football kicking tee
** Two helpers
* Dan built a wooden kicking machine (see photos, above) before completing the steps below.
1. Listen to the weather report and record the temperature, humidity, wind speed, and wind direction.
2. Set up the kicking machine at one end of a flat, open field.
3. Place a tape measure at the edge of the kicking machine. Extend the measuring tape across the field.
4. Fill the football with air using an air pump.
5. Using an air pressure gauge, measure the air pressure inside the football. Add or release air from the football until the gauge measures the manufacturer's recommended level of air pressure: 85 kPa (12 psi).
6. Place the football on the football tee at the front of the kicking machine.
7. Wind up the kicking machine, and "kick" the ball by releasing the machine's wooden "leg."
8. Have two helpers note where the football lands.
9. Record the distance the football traveled. Include units, or your standard of measurement. (Dan used meters to measure distance.)
10. Repeat steps 5 to 9 five more times.
11. Repeat steps 5 to 9 six times each for the following air pressures: 15 kPa (2 psi), 35 kPa (5 psi), 55 kPa (8 psi), 115 kPa (17 psi), and 145 kPa (21 psi).
DRAW A CONCLUSION
Does the distance traveled by the football vary depending on the ball's air pressure? How?
Dan's project led him to a result that would make any football fan cringe: When a football experiences air pressure that is above or below the National Football League's guidelines--between 76 and 90 kPa (11 and 13 psi)--the ball doesn't travel as far when it is kicked.
What would that have meant for the Steelers if the Raiders really had deflated the ball during the height of their rivalry? "It would have been harder for [the Steelers] to make field goals and score points," says Dan.
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|Title Annotation:||PHYSICAL: WRITE A PROCEDURE|
|Date:||Sep 19, 2005|
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