Physics of a Theater Fly System
Colorful stage lights, seamlessly changing background scenery and the opening or closing of a large curtain curtain are often elements of a live-theater performance. Behind the scenes, it takes skilled technicians, multiple integrated systems and physics to make this magic happen.
A fly system is the primary mechanism which allows theater technicians to hang and move curtains, background scenery, lights and more. In this example at the Iowa State University 4-H Youth Development Nutcracker + STEM performance, technicians hung background scenery on special metal pipes which spanned the length of the stage, called “battens.” Because these battens are quite heavy, technicians need a way to balance this weight and also to move the batten up and down quickly and easily as the scenes change during the performance. Steel cables connect the battens to ropes offstage called “handlines.” Attached to the handlines are arbors which hold heavy counterweights. These counterweights are equal to the weight of the arbor. Much like a playground seesaw, having a balance between the arbor and the batten ensures the batten remains safely in place during the performance.
The handlines also run between two pulleys; one on the stage called a “floor block” and one near the ceiling called a “head lock.” Technicians pull the handlines up and down on these pulleys to move the arbors up and down during the performance. The counterweight also assists the technician by making the rope easier to pull.
Iowa Core Standard
Plan an investigation to provide evidence that the change in an object's motion depends on the sum of the forces on the object and the mass of the object
Driving Question
- How does a theater fly system use balanced and unbalanced objects to move stage scenery and lights?
Probing Questions
- How do the counterweights on the arbor help to move the batten?
- Why do the counterweights and the weight of the batten have to be balanced?
- What happens if the counterweights and batten are unbalanced?
Classroom Suggestions
Students could:
- Draw a model of the theater fly system, including where the forces are balanced and unbalanced.
- Visit a local or school theater to see a similar fly system in action.
- Meet local theater stage technicians to discuss how their equipment works similarly or differently from the one shown.
- Watch a recording of a theater performance and notice the points where the fly system is used to change scenery, lights or curtains.
Resources
- Iowa State University | 4-H Nutcracker + STEM: Mouse Trap Design Challenge: In a ballet, there are often set pieces designed and built to help tell the story. This unit allows students to design and build a machine that can catch the Nutcracker Ballet mouse.
- Kaufmann Center | Learn About the Fly System with Don Hovis: This video is a detailed look at all components of the fly system at a large city theater.
- PBS LearningMedia | Iowa PBS Performances: Iowa PBS Performances visits stages and venues across Iowa, showcasing diverse performing arts events—from musical concerts to theater productions—and gives viewers a dynamic and entertaining look behind the curtain. Conversations with performers, peeks behind the scenes, extraordinary videography, and enriching educational sidebars are all part of this comprehensive collection.
- PBS LearningMedia | PBS NC: Newton's First Law of Motion: Find out about Newton's First Law of Motion, plus a little bit of baseball, with this animation.
- Iowa State University | 4-H Nutcracker + STEM: Circuit Challenge: This engineering challenge encourages students to design circuits that will then be a part of a holiday card or Nutcracker set piece.
Contributors
Media produced by Iowa PBS in partnership with Iowa 4-H Youth Development and Stephens Auditorium. Consultation provided by Sam Roberts.
Funding for Iowa Science Phenomena Provided By
