Grade 11 - Force (Rotational Mechanical Systems)

PRESCRIBED LEARNING OUTCOMES

• demonstrate understanding of the relationship between linear force and torque in mechanical systems
• identify units appropriate for measuring torque
• describe the effects of balanced and unbalanced torques on a rotational system
• convert one set of units to another in a mechanical rotational system
• determine various torques by multiplying force times lever arm

SUGGESTED INSTRUCTIONAL STRATEGIES

• Demonstrate torque using a classroom door. Ask students to mark the centre of the door 1 m up from the floor. Have them attach a vacuum suction cup with a hook at the same height but near the knob edge of the door. Then they attach a spring scale to the hook. Pulling on the scale, students measure the force as the door starts to open. They repeat these steps with the suction cup positioned near the hinge edge. Ask them whether one point requires more force than the other to move the door. Students then try several other points on the door, guessing the force needed at each point and measuring it to check their accuracy. Finally, students relate their data to the principle of balanced forces acting on a door.
• Ask students to provide examples of balanced and unbalanced torque operating at home and in the environment, then lead a discussion on torque. Reinforce the idea that torque is a force-like quality in a rotational mechanical system.
• Invite a guest speaker who works with forces and torque in mechanical systems (e.g., steam fitter, physiotherapist, mechanic, architect) to discuss their applications in his or her field. Have students research and write reports on other occupations that use torque in similar ways.
• Ask students to measure the torque on an engine head bolt, record the reading, then remove the bolt. They then replace the bolt and retorque it to the previously measured torque. This activity could be extended by having students apply the same torque using half the length of the handle.

SUGGESTED ASSESSMENT STRATEGIES

• Have students conduct investigations of bolt-tightening sequences in various applications (e.g., engine cylinder head, wheel) and explain the reasons for variation in sequence and torque requirements. In assessing their explanations, look for evidence that students can:
  • identify applications and various tightening sequences
  • provide reasons for torque requirements
  • describe forces on the objects
  • discuss relevant functional or physical factors
• Ask each student to compare and contrast a water wheel with a modern turbine and to report on a chosen aspect. In assessing the reports, look for evidence that students are able to discuss both rotational force applications and torque in relation to the water wheel and turbine.
• Challenge students in pairs to produce problem-solving designs such as:
  • a practical door handle that reduces the force required to turn the latch mechanism and open the door
  • a device to open regular (not child-proof) bottle caps with minimal force
  Work with students to develop criteria they can use to assess their designs. Possible criteria include:
  • practicality of solution
  • ease of use
  • effectiveness of solution (comparing torque required for a standard task with and without the device)

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

• 75 Easy Physics Demonstrations
• Advanced Level Physics, Seventh Edition
• Cambridge Coordinated Science: Physics
• Conceptual Physics, Third Edition
• Heinemann Advanced Science: Physics
• Physics: Principles and Problems, American Edition
• Physics: Principles and Problems, Canadian Edition

• Physics Demonstrations in Mechanics: Parts III - VI

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Last Modified: April 1, 1998.
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