Lesson Notes By Weeks and Term v5 - Grade 7

Lesson Video

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Performance objectives

• Identify types of structures and their properties.
• Explain simple mechanical systems like levers, gears, and pulleys.
• Describe simple control systems (input, process, output).
• Understand and use algorithms and flowcharts.

Lesson summary

This week's Technology lesson focuses on revising and consolidating key concepts covered throughout Grade 7 Technology. Technology is not just about gadgets and computers; it's about problem-solving, design, and making our lives easier and more efficient. In South Africa, a strong understanding of technology is crucial for participating in the modern economy, addressing societal challenges like water scarcity and food security, and contributing to innovation. This revision week is critical to ensure all concepts are understood before moving forward. This week's focus will be on Structures, Mechanical Systems and Control, and Processing.

Lesson notes

2.1 Structures: A structure is something that supports a load or withstands forces.

There are three main types of structures: Frame Structures: These structures are made of interconnected members (beams, columns, struts) that work together to support a load. Think of a soccer goalpost, a bridge, or the frame of a building. Frame structures are strong because the load is distributed throughout the members.

Example:* Eskom's electricity pylons are frame structures designed to withstand strong winds and support heavy electrical cables.

Shell Structures: These structures use a thin, curved surface to provide strength and rigidity. They are strong because the load is distributed across the entire surface. Examples include domes, arches, and eggshells.

Example:* The roof of the Moses Mabhida Stadium in Durban is a shell structure.

Solid Structures: These structures are made of a single, solid piece of material. They are strong because the material itself provides support. Examples include a brick, a rock, or a concrete dam wall.

Example:* A traditional rondavel (round hut) made of clay bricks is a solid structure.

Properties of Structures: Strength: The ability to withstand a load without breaking or deforming.

Stability: The ability to maintain its shape and position under load.

Rigidity: The ability to resist bending or flexing under load. 2.2 Mechanical Systems and Control: Mechanical systems are combinations of parts that work together to perform a specific task.

Key components include: Levers: A rigid bar that pivots on a fixed point (fulcrum) to multiply force. There are three classes of levers, depending on the relative positions of the fulcrum, load, and effort.

Example:* A see-saw (class 1), a wheelbarrow (class 2), and a pair of tongs (class 3).

Linkages: A series of rigid bars connected by pivots, used to transmit motion and force.

Example:* The linkage in a bicycle brake system.

Gears: Toothed wheels that mesh together to transmit rotary motion and force.

Example:* Gears in a bicycle or a car engine.

Pulleys: Wheels with a grooved rim around which a rope or cable passes, used to lift or move heavy objects. Speed Ratio and Mechanical Advantage (Pulleys): Speed Ratio: The ratio of the distance the effort moves to the distance the load moves. It indicates how much faster the effort moves compared to the load. For a pulley system, Speed Ratio = Number of rope segments supporting the load.

Mechanical Advantage (MA): The ratio of the load force to the effort force. It indicates how much the pulley system multiplies the effort force. MA = Load / Effort. Ideally, MA = Speed Ratio.

Example 1:* A pulley system has 3 rope segments supporting the load. If you pull the rope 6 meters, the load is lifted 2 meters. Speed Ratio =

3. If you lift a load of 300N with an effort of 100N, the Mechanical Advantage = 300N/100N =

3. Control Systems: A control system regulates a process.

It typically consists of: Input: Something that triggers the system (e.g., a button, a sensor).

Process: The action that the system performs (e.g., heating water, turning on a light).

Output: The result of the process (e.g., hot water, light).

Example:* A geyser.

Input: Low water temperature (sensed by a thermostat).

Process: Heating the water.

Output: Hot water. 2.3 Processing: Algorithms and Flowcharts: An algorithm is a step-by-step set of instructions to solve a problem or achieve a specific outcome. A flowchart is a visual representation of an algorithm, using symbols to represent different types of instructions.

Common Flowchart Symbols: Start/End: Oval shape.

Process: Rectangle shape.

Decision: Diamond shape.

Input/Output: Parallelogram shape.

Flow Lines: Arrows showing the sequence of steps. Example Algorithm and Flowchart (Making a cup of tea):* Algorithm: Start Boil water Put tea bag in a cup Pour boiling water into the cup Add milk and sugar (optional) Stir End (Imagine a Flowchart here with the correct symbols for each step.) Guided Practice (With Solutions)

Question 1: Identify the type of structure used in the following: a) a bridge, b) a plastic water bottle, c) a brick wall.

Solution: a)

Bridge: Frame structure b)

Plastic water bottle: Shell structure c)

Brick wall: Solid structure

Commentary: This question tests the ability to identify the basic structural types. Understanding the characteristics of each type is key.

Question 2: A pulley system has 4 rope segments supporting the load. If you want to lift a load of 400N and the system is ideally efficient, what effort force is required? What is the speed ratio of the system?

Solution: Mechanical Advantage (MA) = Load / Effort Since the system is ideal, MA = Speed Ratio = Number of rope segments = 4 Therefore, 4 = 400N / Effort Effort = 400N / 4 = 100N Speed Ratio = 4

Commentary: This question combines the understanding of Mechanical Advantage, Load, and Effort forces in a pulley system.

Question 3: Describe the input, process, and output in a solar water heater.