Grade 8 Unit D: Curriculum Links | Print |

Unit D: Mechanical Systems
(Science and Technology emphasis)

Machines are used for many purposes in our daily lives, when we need to transfer energy into motion, or move materials in a controlled way. in learning about mechanical devices, students investigate how components are linked so that energy is transferred efficiently and desired functions are performed. A comparison of past and present technologies helps students recognize that different approaches have been used over time to meet common needs. Evaluation of efficiency, effectiveness and impacts on daily life, the community and the environment are important considerations in this unit.

Focusing Questions:

How is energy transferred in mechanical devices?

How do they provide for controlled application of energy in ways that are efficient, effective and responsible?

Key Concepts

  • design and function
  • systems and subsystems
  • transmission of force and motion
  • simple machines
  • mechanical advantage
  • speed ratios and force ratios
  • mechanical advantage and hydraulics
  • measurement of work in joules

STS and Knowledge Outcomes
Students will: Illustrate the development of science and technology by describing, comparing and interpreting mechanical devices that have been improved over time
investigate and provide examples of mechanical devices used in the past to meet particular needs (e.g., describe and interpret example devices developed to move water or be moved by water, such as the Persian wheel, Archimedes wheel, mill wheel)
illustrate how a common need has been met in different ways over time (e.g., development of different kinds of lifting devices)
illustrate how trial and error and scientific knowledge both play a role in technological development (e.g., development of aircraft)

Students will:
Analyze machines by describing structures and functions of the overall system, the subsystems and the component parts

analyze a mechanical device
identify the overall function of the device
describe the contribution of individual components or subsystems to the overall function of the device
identify components that operate as simple machines
identify the source of energy for some farniliar mechanical devices
identify linkages and power transmissions in a mechanical device and describe their general function (e.g., identify the purpose and general flinction of belt drives and gear systems within a mechanical device)

Students will:
Investigate and describe the transmission of force and energy between parts of a mechanical system analyze mechanical devices to determine speed ratios and force ratios

build or modify a model mechanical system to provide for different turning ratios between a driving and driven shaft, or to achieve a given force ratio
compare theoretical and actual values of force ratios and propose explanations for discrepancies (e.g., identify frictional forces and estimate their effect on efficiency)
identify work input and work output in joules for a simple machine or mechanical system (e.g., use a device to hft a measured mass an identified distance, then calculate the work output)
describe fluid pressure qualitatively and quantitatively
explain how forces are transferred in all directions
describe pressure in units of force per unit area
describe how hydraulic pressure can be used to create a mechanical advantage in a simple hydraulic jack (e.g., describe the relationship between force, piston size and distance moved using different sized syringes linked by tubing)
describe and interpret technologies based on hydraulics and pneumatics (e.g., applications in earthmoving equipment; application to tools powered by compressed air)

Students will:
Analyze the social and environmental contexts of science and technology, as they apply to the development of mechanical device

evaluate the design and function of a mechanical device in relation to its efficiency and
effectiveness, and identify its impacts on humans and the environment
develop and apply a set of criteria for evaluating a given mechanical device, and defend those
criteria in terms of relevance to social and environmental needs
illustrate how technological development is influenced by advances in science, and by changes in society and the environment