Lesson Notes By Weeks and Term v5 - Grade 7

Lesson Video

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Performance objectives

• Identify and explain different types of structures.
• Describe the purpose and function of different mechanisms.
• Explain the basic components of a system.
• Define input, process, and output in technological systems.
• Explain the role of control in a system.

Lesson summary

This week focuses on revising and consolidating core Technology concepts we've covered so far in Grade

7. Technology is everywhere in South Africa, from the cellphones we use to communicate, to the infrastructure that provides us with electricity and clean water. Understanding the principles of technology allows us to be more informed citizens, better able to solve problems in our communities and contribute to a more sustainable future. We'll be revisiting topics like structures, mechanisms, systems and control. This revision is vital for building a strong foundation for more advanced technological concepts in higher grades and understanding how things work around us.

Lesson notes

2.1 Structures: A structure is something that has a definite size and shape, which serves a definite purpose or function and can withstand forces acting on it. Structures are designed to support loads.

Types of Structures: Frame Structures: Made of separate members joined together to form a framework. They're good at supporting loads applied at specific points. Think of a bicycle frame, electricity pylon, or a roof truss. In South Africa, frame structures are commonly used for low-cost housing solutions. The joints in frame structures are often the weakest points, so their design and the materials used are important.

Shell Structures: These are hollow, with a curved outer surface. They are strong because the load is distributed over the entire surface. Examples include eggshells, car bodies, and domes like the one at the Union Buildings in Pretoria. These shapes provide strength and protection with less material than solid structures.

Solid Structures: These are made of a single, solid piece of material. They're generally strong but can be heavy and use a lot of material. Examples include bricks, dams, and mountains. The walls of a traditional rondavel are examples of a solid structure that is well-suited to the South African climate.

Forces on Structures: Tension: A force that pulls or stretches a material.

Compression: A force that pushes or squeezes a material.

Shear: A force that causes one part of a material to slide past another part.

Torsion: A twisting force.

Bending: A combination of tension and compression.

Example: Consider a bridge. The bridge's supports experience compression as they hold the weight of the traffic. The cables of a suspension bridge experience tension. Strong materials like steel are used because they can withstand these forces. 2.2 Mechanisms: A mechanism is a device that changes motion or force. They make work easier.

Types of Mechanisms: Levers: A rigid bar that pivots around a fixed point (fulcrum). They can be used to multiply force. Think of a see-saw (teeter-totter), a crowbar, or a pair of pliers. South African examples include using a lever to lift a heavy rock while gardening or a wheelbarrow used in construction. There are three classes of levers, classified by the relative positions of the fulcrum, load, and effort.

Gears: Toothed wheels that mesh together to transmit rotary motion. They can change the speed, torque, and direction of rotation. Gears are found in bicycles, cars, and watches. Gears are essential in mining equipment to provide high torque for drilling and excavation.

Pulleys: Wheels with a grooved rim around which a rope or belt can pass. They can change the direction of force and multiply force. Think of a flagpole, a crane, or a block and tackle used to lift heavy objects. In many rural South African communities, pulleys are used to lift water from wells.

Mechanical Advantage: The ratio of the output force to the input force. Mechanisms allow us to exert less force to achieve the same result.

Example: Imagine using a long crowbar (lever) to lift a heavy rock. By using the lever, you apply a smaller force over a longer distance to lift the rock, achieving a mechanical advantage. 2.3 Systems and Control: A system is a collection of interacting parts that work together to achieve a specific goal. Systems have inputs, processes, and outputs.

Input: What goes into the system (e.g., energy, materials, information).

Process: What the system does to the input (e.g., transforming, converting, processing).

Output: What comes out of the system (e.g., a product, a service, information).

Control: How the system is regulated to ensure it operates correctly and achieves its desired outcome. Control mechanisms can be automatic (like a thermostat) or manual (like a volume knob on a radio).

Example: Consider a solar water heater.

Input: Sunlight (energy) and cold water.

Process: The solar panels absorb sunlight and heat the water.

Output: Hot water.

Control: A thermostat monitors the water temperature and turns off the heating process when the desired temperature is reached.

Example: A Computer System Input: Keystrokes from the keyboard, mouse clicks, data from files.

Process: The CPU processes the input using software instructions.

Output: Display on the screen, printed documents, sound from speakers.

Control: The operating system manages the resources and ensures the smooth operation of the entire system. Guided Practice (With Solutions)

Question 1: Identify the type of structure used to build a typical cellphone tower in South Africa. What forces are acting on this structure, and how is the structure designed to withstand these forces?

Solution: Type of Structure: A cellphone tower is primarily a frame structure.

Forces: The main forces acting on the tower are: Compression: Due to the weight of the tower itself and any equipment attached to it.

Tension: From the wind pulling on the tower, especially during strong winds.