Grade 11 - Force (Linear Mechanical Systems)

PRESCRIBED LEARNING OUTCOMES

• design, construct, and calibrate devices capable of measuring force
• describe the role of forces in common situations
• identify units appropriate for measuring forces
• explain the importance of force direction and magnitude
• describe the effects of balanced and unbalanced forces on objects
• distinguish between scalar and vector quantities
• use vector analysis to solve problems involving parallel forces
• apply different forces to an elastic object, measure the extension, plot the data, and interpret the results

SUGGESTED INSTRUCTIONAL STRATEGIES

• Throw a toy parachutist into the air. Discuss how the concept of unbalanced and balanced forces relates to the rate at which a parachutist falls. Form pairs and have each pair develop an explanation for what causes a parachutist to reach terminal velocity and why this value is lower when a parachute is open. Ask pairs to present their explanations to the class. Have students use diagrams to represent the forces acting on the parachutist as vectors.
• Create a slingshot by clamping an elastic band to a desk at two points. Propel a wad of paper into the air three times, each time pulling the band back in a different direction, left or right, thus changing the direction of flight. Ask students to describe the relation between the direction of flight and the direction that the elastic band was pulled back. As a class, identify situations in everyday life in which an understanding of forces is useful.
• Conduct a site visit to analyse how houses, buildings, and bridges are designed to ensure that all forces acting on them are balanced to keep the structures in equilibrium. As a follow-up, ask students in groups to construct models of structures such as bridges or towers.
• Have students use simple springs or elastic bands to design and construct devices capable of measuring force. Ask them to calibrate their devices, showing the force applied, then participate in a science challenge to see which device is most accurate.

SUGGESTED ASSESSMENT STRATEGIES

• Ask each student to determine a means of measuring the forces involved in a linear mechanical system by investigating the operation of a parachute, or the effects of helium versus CO2 in a balloon. Observe the extent to which students use the following terms appropriately in their descriptions:
  • unbalanced and balanced forces
  • vector or scalar quantities
  • direction of forces
• To check students' understanding of relationships between the extension or compression of a spring, the magnitude of the spring constant, and their applications, have students report on these factors in applications such as dump-truck helper springs, automobile springs, spring-door closures, and one application of their own choosing. In assessing students' reports, determine the extent to which they are able to:
  • explain the spring's function in each application
  • describe the forces acting in each situation
  • plot the relationships between force and the extension or compression
• Have students use their self-assessment journals to reflect on relationships and concepts of linear force in a mechanical system. Guiding comments might include:
  • In this session I learned __________________.
  • I would describe the effect that linear forces have on mechanical systems as __________________.
  • One question I still have is __________________.
  Note the extent to which students' journal entries indicate understanding of linear forces. Also note any areas of possible confusion or uncertainty. This information could be used as a basis for later review.

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

• Hidden by Time: Seeing the Physical World with High-Speed Cameras
• Physics Demonstrations in Mechanics: Parts III - VI

• Interactive Physics: Student Edition

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Last Modified: April 1, 1998.
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