4

Students are asked to design simple yet accurate timing devices using limited supplies. The challenge is to create a device that measures out a time period of exactly three minutes. They brainstorm ideas using the different materials provided. Students observe and explain the effects of conservation of energy.

Engineers continually challenge themselves to make better and more accurate devices, tools, systems and processes, including timing devices.. conservation of energy energy engineering design process harmonic motion kinetic energy period potential energy simple harmonic motion timing challenge Describe the engineering design process. Explain the concept of conservation of energy in relationship to kinetic and potential energy. Describe simple harmonic motion. stop watch, for testing purposes only string or shoelaces paper cardboard paperclips soap glue coins paper cups soda bottles Student Handout Students may bring in up to three additional simple items. Do not allow clocks, watches, or any other devices that have pre-made timers. You have been taken prisoner in a foreign country. You are going to try to escape from the prison. In order to escape, you must time the movements of the guards exactly! You have to design a method of timing three minutes (the time it takes the guards to change posts) so you can make your break. You will be able to use a timing device to check the accuracy of the device. No clock/watch may be used in the device itself. You will be graded on how close you come to the three minutes. Good Luck! A series of steps used by engineering teams to guide them as they solve problems: define the problem, come up with ideas (brainstorming), select the most promising design, plan and communicate the design, create and test the design, and evaluate and revise the design. Also called the design-build-test loop. The energy of a moving body. The energy stored in a system. Energy can neither be created nor destroyed. A repeated motion around a central equilibrium position. A device with a mass attached to a fixed that oscillates around an equilibrium position. Maximum displacement from the equilibrium position. The time it takes to complete one cycle of motion (back and forth). Gather materials and make copies of the Student Handout. Read outloud the challenge (the Motivation/Introduction section) to the class. Divide the class into groups of four students each. Distribute the materials and handouts. (As described on the attached Student Handout...) In groups, brainstorm ideas to complete the task (record all ideas). Make a list of three materials you would like to bring from home (cannot include a timing device). Choose the best solution. Get approval from your teacher on additional materials being brought in. Explain why that solution was chosen. Sketch your solution. Build a prototype Test the prototype (record time). Redesign to get a more accurate time. Pre-Activity Vocabulary Quiz (doc) Pre-Activity Vocabulary Quiz (pdf) Example Grading Scale (doc) Example Grading Scale (pdf) Student Handout (doc) Student Handout (pdf) Do not permit use of candles or any type of open flame due to their fire hazard. Check that student designs do not include materials that might be safety hazards, such as falling objects, splashing water, etc. Quiz: Before beginning the activity, administer the attached quiz to gauge students' initial understanding of the vocabulary terms and concepts. Observe teamwork. Observe brainstorming and decision making processes. Note students' ability to observe and understand when the existence of kinetic and potential energy is in the system. Note how students fill in the handout blanks and questions to gauge their comprehension. Base the grades for the devices on how close to three minutes students are able to measure time with their devices. See the attached Example Grading Scale for a suggestion on how to assign points. Homework Questions: Assign students to answer for homework the concluding questions found at the end of the attached Student Handout. Review as a class the next day. When did your system have potential energy and when did it have kinetic energy? Were you able to observe conservation of energy in your system? If not, explain how it was conserved. Did your device follow simple harmonic motion? Explain. Ask students to analyze the reasons for success or failure of their devices. Discuss possible ways to improve accuracy of the devices. Provide time for 2-3 redesigns. For lower grades, use a grading rubric that is more lenient to timing errors. For higher grades, permit fewer errors in timing.