Structures and Mechanisms
The Structures and Mechanisms strand is largely technological in
content. A structure is any form that resists forces that would cause it to
change shape and size. A mechanism uses or creates motion and consists of one
or several simple machines (e.g., lever, pulley, wheel) that perform a specific
function. With successive grade levels, students gain greater sophistication in
their understanding of structures and mechanisms, and skill in their ability to
design and construct them. Students also learn that structures and mechanisms
can be combined into a system, which is a set of connected parts whose action
is controlled in specific ways – for example, the brake system on a
bicycle or car, or the electrical system in a house.
The topics covered in this strand are:
Grade 1: Everyday Structures
Grade 2: Movement
Grade 3:
Stability
Grade 4: Pulleys and Gears
Grade 5: Forces Acting on
Structures and Mechanisms
Grade 6: Motion
Grade 7: Structural Strength
and Stability
Grade 8: Mechanical Efficiency
Throughout this strand, students pursue many types of investigation
that involve them in designing and building structures and mechanisms, and
testing the results of their designs. Using their observations, students
describe various kinds of forces and motion that affect their designs. In
investigating the operation of systems, students identify the parts of a system
and understand their function. They then use this knowledge to understand the
operation of the system as a whole and to deal with problems and modifications
relating to specific parts.
Students make links to the real world when they evaluate real examples
of structures and mechanisms using not only performance criteria (e.g.,
strength) but also other criteria such as aesthetic and ergonomic qualities,
cost of production, safety, and reliability. Students can make links to the
Matter and Materials strand and the Energy and Control strand, as well as the
social studies area of the curriculum (e.g., through consideration of
structures designed by people in other cultures). Communication in this strand
takes place through graphic design, demonstrations, and media works, as well as
written and oral descriptions of structures and mechanisms.
It is important that students follow established safety practices in
designing, constructing, and experimenting with structures and mechanisms.
These practices include:
- using tools safely to cut, join, and shape objects;
- handling moulding clay correctly and washing one’s hands after
using it;
- following proper procedures when comparing mechanical systems and
their operation;
- using care when observing and working with objects in motion (e.g.,
objects that are spinning, swinging, bouncing, vibrating; gears and pulleys;
elevated objects).
Structures and Mechanisms:
Grade 7 - Structural Strength and Stability
Overview
In previous grades, students will have investigated, designed, built,
and tested a variety of structures. In Grade 7, they will learn more about the
effects of forces that act on and within different structural forms. Using
increasingly sophisticated techniques, students will continue to investigate
how different structural forms support or withstand loads by designing,
building, and testing solid (or mass) structures, shell structures, and frame
structures.
Overall Expectations
By the end of Grade 7, students will:
- demonstrate an understanding of the relationship between the
effectiveness of structural forms and the forces that act on and within them;
- design and make a variety of structures, and investigate the
relationship between the design and function of these structures and the forces
that act on them;
- demonstrate an understanding of the factors (e.g., availability of
resources) that must be considered in the designing and making of products that
meet a specific need.
Specific Expectations |
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Understanding Basic Concepts
By the end of Grade 7, students will:
- classify structures as solid (or mass) structures (e.g.,
dams), frame structures (e.g., goal posts), or shell structures (e.g., airplane
wings);
- demonstrate awareness that the position of the centre of
gravity of a structure (e.g., bridge, building, tower) determines whether the
structure is stable or unstable;
- describe, using their observations, ways in which different
forces can affect the stability of a structure (e.g., certain forces may cause
a structure to shear, twist, or buckle);
- demonstrate awareness that the effect of forces acting on a
structure under load depends on the magnitude, direction, and point and plane
of application of the forces;
- identify forces within a structure that are affected by
forces outside the structure (e.g., shear, torsion, tension, and compression
within a bridge are affected by external forces such as high wind or ice);
- measure the performance of a structure (e.g., a bridge, a
tower) by comparing its mass with the mass of the load it supports.
Developing Skills of Inquiry, Design, and
Communication
By the end of Grade 7, students will:
- use appropriate techniques and materials (e.g., cutting and
joining pieces of wood or plastic) while making structures that have
mechanisms;
- formulate questions about and identify needs and problems
related to the strength of structures, and explore possible answers and
solutions (e.g., determine what caused structural failure and propose ways of
supporting a specific load);
- 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 terms such as fields, data, and cells when describing databases);
- compile qualitative and quantitative data gathered through
investigation in order to record and present results, using diagrams, flow
charts, frequency tables, bar graphs, line graphs, and stem-and-leaf plots
produced by hand or with a computer (e.g., tabulate data from tests of the
strength of their own structures; record their evaluations of possible
solutions to a design problem);
- communicate the procedures and results of investigations for
specific purposes and to specific audiences, using media works, written notes
and descriptions, charts, drawings, and oral presentations (e.g., create an
animated film of the steps taken in designing and making a product).
Relating Science and Technology to the World Outside the
School
By the end of Grade 7, students will:
- tell the “story” of a product used every day,
identifying the need it meets and describing its production, use, and eventual
disposal;
- investigate ways in which research is done on existing
products (e.g., basketball shoes, telephones) to generate new ideas for the
products;
- recognize the importance of researching needs and
opportunities for sale before proposing ways of developing a product;
- recognize that a solution to a problem may result in
creating new problems in other areas, and that a solution to a problem may be
found while one is working on solving a problem in another area;
- identify energy as a significant cost in the manufacturing
and use of products or systems;
- produce a work plan that outlines the possible criteria for
choosing resources for manufacturing a product that they have designed (e.g.,
the properties and availability of the resources; the aesthetic appeal of the
product and the impact of its use on the environment);
- describe, using their observations, the function of
symmetrical design in structural and mechanical systems (e.g., in bridges);
- use their knowledge of materials in designing and making
structures that will stand up to stress;
- demonstrate how information is organized and stored in a
computer system (e.g., in a database or a spreadsheet program).
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