Science and Technology
Grade 8: Structures and Mechanisms: Mechanical Efficiency
Overall Expectations
•demonstrate an understanding of the factors that contribute to the efficient operation of mechanisms and systems;
•design and make systems of structures and mechanisms, and investigate the efficiency of the mechanical devices within them;
•demonstrate understanding of the factors that can affect the manufacturing of a product, including the needs of the consumer.         
Specific Expectations
Understanding Basic Concepts        
•explain how forces are transferred in all directions in fluids (Pascal’s law);        
•describe in quantitative terms the relationship between force, area, and pressure;        
•explain in qualitative terms the relationship between pressure, volume, and temperature when a liquid is compressed or heated and a gas (e.g., air) is compressed or heated;        
•compare the effect of pressure on a liquid (e.g., on water in a syringe) with the effect of pressure on a gas (e.g., on air in a syringe);        
•explain, using their observations, how the use of appropriate levers and ways of linking the components of fluid systems can improve the performance of the systems (e.g., systems in a steam shovel, in a robot);        
•investigate and measure forces that affect the movement of an object (e.g., friction);        
•distinguish between velocity and speed (i.e., define velocity as speed in a given direction);        
•determine the velocity ratio of devices with pulleys and gears (i.e., divide the distance that a load moves by the distance covered by the force (effort) required to move it);        
•predict the mechanical efficiency of using different mechanical systems (e.g., a winch).         
Developing Skills of Inquiry, Design, and Communication        
•formulate questions about and identify needs and problems related to the efficient operation of mechanical systems, and explore possible answers and solutions (e.g., test a device at each stage of its development and evaluate its performance in relation to specific criteria);        
•plan investigations for some of these answers and solutions, identifying variables that need to be held constant to ensure a fair test and identifying criteria for assessing solutions;        
•use appropriate vocabulary, including correct science and technology terminology, to communicate ideas, procedures, and results (e.g., use such technical terms as velocity, velocity ratio, and efficiency);        
•compile qualitative and quantitative data gathered through investigation in order to record and present results, using diagrams, flow charts, frequency tables, graphs, and stem-and-leaf plots produced by hand or with a computer (e.g., produce and analyse a quotation to complete a job in the home);        
•communicate the procedures and results of investigations for specific purposes and to specific audiences, using media works, written notes and descriptions, charts, graphs, drawings, and oral presentations (e.g., make a display in which they compare the ways in which a closed pneumatic system and a hydraulic system operate the same size of cylinder);        
•design and make a mechanical system that is operated by hydraulic or pneumatic power;        
•select and use appropriate materials and strategies to make a product;        
•produce technical drawings and layout diagrams of a structure or a mechanical system that they are designing, using a variety of resources.         
Relating Science and Technology to the World Outside the School        
•explain how human weight, height, age, sex, and physical capability affect the design of products (e.g., car seats, snowmobiles, zippers);        
•analyse the use of symmetry in the ergonomic design of objects and systems (e.g., office furniture, computer equipment);        
•describe how the components and subsystems of a product used by humans (e.g., a bicycle, a computer system) enable the product to function;        
•identify the kinds of information that assist consumers in making a decision about buying a product (e.g., information on performance, durability, safety, benefits to health);        
•identify consumer expectations regarding the function and effectiveness of a product, using information collected in a survey they made, and recognize that expectations may change;        
•recognize the importance of unbiased testing of control samples and independent evaluation of the test results before a product is manufactured;        
•identify the personal and societal factors that determine whether a product is used;        
•evaluate product manuals or help screens (e.g., a manual for a video recorder), focusing on clarity, thoroughness, and general “user-friendliness”, and identify ways of making the product easier to use;        
•assess the impact on the environment of the use and disposal of various products (e.g., motor oil, Freon);        
•explain the economic, social, and environmental factors that can determine whether a product is manufactured (e.g., costs of materials and equipment, availability of skilled labour, potential harmfulness of the product);        
•make informed judgements about products designed and made by others;        
•evaluate their own designs against the original need, and propose modifications to improve the quality of the products.         
Student Name:        
 Expectations: Copyright The Queen's Printer for Ontario, 1998.  Format: Copyright B.Phillips, 1998.