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9th Grade Trebuchet Project Explores the Physics of Medieval Warfare

Monday, May 14, 2018

Science and medieval history met in the halls of Heathwood's Upper School this month in the 9th grade's trebuchet project.

At the end of the year, students in the 9th grade Physics 1 and World History classes complete a cross-curricular project involving the very successful medieval siege engine known as a trebuchet.  In their history class the students study life in medieval castles as well as the innovations made by early engineers in the area of mechanized warfare. After conducting extensive research, they complete a formal research paper.  The other side of this joint project involves the students building a tabletop trebuchet in their Physics 1 class. Arguably the most effective and long lived weapon used during sieges on opposing castles, the trebuchet works by converting gravitational potential energy of a falling weight into the kinetic energy of a projectile aimed at an opposing castle.


In the physics side of the project the students must test-fire their trebuchet while carefully analyzing the physics involved.  Students vary the amount of counter weight and study the range of the fired projectile associated with each amount of weight. The data collected during the test firing is used by the students to construct graphs that relate the range of the projectile to the amount of weight driving the throwing arm.  

On the day of the firing competition, the teams are assigned a random distance from a mock castle constructed of cardboard for the occasion.  This random distance adds realism to the project as the students have learned in their history class that trebuchets were built on-site just outside the castle walls.  The engineers would try to get as close as possible -- but of course the defending army did their best to keep the invaders as far from the castle as possible. Teams must use the graphs generated during the testing phase to determine the correct amount of counterweight to use based on the randomly assigned distance from which they will be firing on the castle.

Each team has a limited amount of time to study their physics data before taking three scored shots at the castle. Each area of the target castle is assigned a diminishing point value with the center of the castle scoring the highest points.  There is no trial and error option for the first shot although adjustments are allowed between each of the three shots. Making all three shots count requires good physics and accurate data analysis from the testing phase.

Parts of the research paper written in their history class becomes the background and literature survey portion of a formal lab report that is submitted after the competition.  This interdisciplinary project is a fun way to end the year and brings together the formal research paper writing skills of their history class with a wrap up and review of many of the skills and principles studied during the year in their Physics 1 class.