Lesson Notes By Weeks and Term v5 - Grade 7
Structures: types of structures and simple frame structures – Week 3 focus
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Structures: types of structures and simple frame structures – Week 3 focus
Download the Lessonotes Mobile South Africa app for faster lesson access on Android and iPhone.
Subject: Technology
Class: Grade 7
Term: 1st Term
Week: 3
Theme: General lesson support
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This week, we're diving into the fascinating world of structures! Structures are all around us, from the houses we live in to the bridges we cross and even the desks we use in the classroom. Understanding how structures are designed and built is crucial because it helps us understand how things stay standing, support weight, and resist forces. In South Africa, knowing about structures is particularly important. We need well-built homes that can withstand different weather conditions, safe bridges for transportation, and strong infrastructure to support our growing economy. Poorly built structures can be dangerous and costly.
What is a Structure? A structure is anything that is built or made with a definite size and shape for a specific purpose. Its purpose is to withstand forces and loads that are applied to it without failing.
Types of Structures: There are three main types of structures: Solid Structures: These are made of solid materials and rely on their own weight and mass to maintain their shape and stability.
Examples: A brick wall, a statue, a mountain. Think of a brick holding itself up – it's the solid material resisting gravity.
Shell Structures: These are hollow structures with a curved outer surface that provides strength and rigidity. The curved shape helps to distribute forces evenly across the structure.
Examples: An eggshell, a plastic bottle, a stadium dome. In South Africa, corrugated iron sheets used for roofing in many communities act as shell structures once installed with a curve.
Frame Structures: These are made of interconnected parts, or members, that form a framework. They rely on the arrangement of these members to provide strength and stability.
Examples: A bicycle frame, a bridge, a building frame, a soccer goal. Frame structures are very common because they can be strong and lightweight.
Focus on Frame Structures: Frame structures are made up of individual components joined together. These components can be made of wood, steel, plastic, or other materials. The way these components are joined and arranged is crucial for the structure's strength.
The most common components include: Beams: Horizontal members that support loads along their length.
Columns: Vertical members that support loads from above.
Struts: Diagonal members used to provide support and stability.
Joints: The points where the members are connected.
Triangulation and Stability: The key to making a frame structure strong and stable is triangulation. A triangle is the strongest shape because its angles cannot change without changing the length of its sides. If you apply a force to one corner of a triangle, the force is distributed equally along all three sides. This makes it very resistant to distortion. If you try to push a square out of shape, it's easy to do so. But if you add a diagonal member to create two triangles, the square becomes much stronger and more rigid. That diagonal member is a strut.
Forces Acting on Structures: Structures are constantly subjected to forces that can affect their stability. Understanding these forces is important for designing strong structures.
The main types of forces are: Tension: A pulling or stretching force. Imagine pulling on a rope – the rope is in tension.
Example: Cables supporting a suspension bridge.
Compression: A pushing or squeezing force. Imagine pushing down on a stack of books – the books are in compression.
Example: A column supporting a roof.
Shear: A force that causes one part of a material to slide past another part. Imagine cutting paper with scissors – the paper is being subjected to shear forces.
Example: A bolt connecting two pieces of wood being pulled apart.
Torsion: A twisting force. Imagine twisting a wet cloth to wring out the water – the cloth is being subjected to torsion.
Example: The axle of a car when the wheels turn.
Bending: A combination of tension and compression that occurs when a beam or other structural member is loaded. The top of the beam is in compression, and the bottom is in tension. Imagine a diving board being loaded. The top part gets pushed together (compression), while the bottom part stretches (tension).