Grade 12 - Transformers (Mechanical Systems)

PRESCRIBED LEARNING OUTCOMES

• design and construct a device that alters force and explain where it could be applied within a system
• distinguish between ideal and actual mechanical advantage
• distinguish between efficiency and mechanical advantage
• determine the mechanical advantage and efficiency of:
  • a wheel and axle
  • a pulley system
  • an inclined plane
  • a belt-and-gear-driven system
• describe the three classes of levers and explain the advantage of each

SUGGESTED INSTRUCTIONAL STRATEGIES

• Have students in groups design and construct devices that use at least two simple machines to move a person from one place to another (e.g., to move a disabled person) or to help a person perform a specific task.
• Divide the class into small groups and have each group set up a different pulley system, using pulleys of various qualities and different grades of string or rope. Ask groups to examine each system and determine actual mechanical advantage (AMA), ideal mechanical advantage (IMA), and efficiency.
• Ask students to identify situations in which efficiency might be lost in wheel-and-axle, belt-and-gear-driven, pulley, and lever systems. Ask them to identify methods of increasing efficiency in each. Discuss the results as a class.
• Have students work in groups to design and demonstrate lever systems that can lift a car high enough to change a tire. Discuss the results of each demonstration with the class.
• Have students in groups design systems that will allow a person to apply 250 N of force to lift a 100-kg boat onto the top of a car, and identify components they could use to construct the system for under $500. Ask them to present their designs to the class as models or diagrams, and to discuss the advantages and disadvantages of each.

SUGGESTED ASSESSMENT STRATEGIES

• Have students in groups design devices that alter force, then have each group explain its operation and calculate the mechanical advantage. Ask questions such as:
  • How could the device be improved?
  • How can the mechanical advantage be increased?
  • What are possible applications for this device?
  Note the extent to which students' responses:
  • use appropriate scientific vocabulary
  • correctly identify types of mechanical transformation
  • differentiate between efficiency and mechanical advantage
• Have students present oral or written reports examining advantages and disadvantages of fixed-gear and 12- and 18-gear systems for bikes. Look for evidence that students can:
  • determine mechanical advantage in each case
  • include efficiency determinations
  • consider appropriate contexts for each gear system
  • discuss advantages and disadvantages of each system
• Ask students to work in groups to design tests that rate wheelbarrows for criteria such as ease of operation and load-carrying capacity. As students work on their test designs, check their understanding by asking questions such as:
  • How would you determine the IMA and the AMA?
  • What are all the components that should be analysed?
  • Would there be an improvement if the lever class were changed?
  • What aspects of the test allow for a valid comparison between wheelbarrows?
  When assessing students' responses, note the extent to which they are able to:
  • identify significant attributes of devices that affect performance
  • develop effective and reliable testing procedures

RECOMMENDED LEARNING RESOURCES

Applications of Physics 11 and 12 develops an understanding of the concepts of physics through the design, construction, and use of a variety of devices. Although the resources listed below provide a range of teaching and learning opportunities in physics, none of them provide a comprehensive resources package that completely supports the philosophy and approach of the British Columbia curriculum in the applications of physics. Please see the Appendix B Introduction for further information.

Print Materials

• Cambridge Coordinated Science: Physics
• Conceptual Physics, Third Edition
• Physics: Principles and Problems, American Edition
• Physics: Principles and Problems, Canadian Edition

• Interactive Physics: Student Edition

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Last Modified: April 1, 1998.
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