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Kelly, a mathematics and science teacher at Sumner High School in Sumner, Washington, teaches a hands-on, project-based physics class. One such project—to build and test a life-size trebuchet, catapult, or ballista—culminates a unit on projectile motion. This year, NOVA's "Secrets of Lost Empires: Medieval Siege" program aired just before Kelly started his unit. Students first received directions for the final project and submitted a detailed sketch and materials list for approval. During the six-day unit, students examined how projectiles moved in two dimensions and wrote parametric equations to describe the motion. Students investigated the relationship between the angle in which an object is launched and the distance traveled. Through this exercise, coupled with prior work on vectors, students learned that the horizontal component of the motion is not affected by the vertical component of the motion. Although Kelly has taught the projectile motion unit for the past three years, this year students did something different—they viewed the "Medieval Siege" program. Kelly liked the way the program shows how engineers think through a problem and problem solve and tinker until the end result is achieved. Feedback was immediate—students voiced their enthusiasm right away. Working individually or in teams of two, students constructed their final projects outside of class time. During the final two class days of the unit, students completed testing and fine-tuning their trebuchets and then pitted them against their peers. During the competition, teams launched three water balloons 164 feet (50 meters) towards an appealing target—their teacher seated in a chair (with lots of protection, including a helmet and a very thick jacket). Two concentric circles, each 3.28 feet (1 meter) in radius, radiated outward from Kelly. Points were awarded for those whose balloons came closest to Kelly (whose luck is holding; he has not been hit by a balloon yet). Students then wrote equations for each of their three launches. This year Kelly, who has been teaching for 15 years, was impressed by the number of student teams that chose to build the trebuchet and the overall quality of students' projects. When asked about the difference between this and past years' efforts, students credited the NOVA program with inspiring them and acting as a catalyst for motivating them to do further research. Kelly's take on it? "It is lots of fun and they get REAL excited when the balloons land close." For more information about Kelly's project, you can contact him at: Bruce Kelly
—Kristina Ransick
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