Lesson Notes By Weeks and Term v5 - Grade 9

Lesson Video

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Performance objectives

• Analyze simple mechanical systems with gears and levers.
• Design a basic electrical circuit using a transistor as a switch.
• Describe the function of a microcontroller.
• Differentiate between open-loop and closed-loop systems.
• Explain the role of sensors in automated systems.

Lesson summary

This week, we delve deeper into systems and control, focusing on more complex mechanical and electrical systems. Understanding these systems is crucial because they are the building blocks of many technologies we use daily, from the traffic lights that keep our roads safe to the security systems protecting our homes and businesses. South Africa, as a developing nation, requires skilled individuals who can design, maintain, and improve these systems to drive economic growth and improve quality of life. A strong grasp of these concepts will equip you to solve practical problems and contribute to the technological advancement of our country.

Lesson notes

2.1 Gears and Levers: Gears are toothed wheels that transmit rotational motion and force. They are used to change the speed, torque, or direction of rotation. The gear ratio is the ratio of the number of teeth on the driven gear (output) to the number of teeth on the driving gear (input). Gear Ratio (GR) = Number of teeth on driven gear / Number of teeth on driving gear If GR > 1, the output speed decreases, and the output torque increases (speed reduction, torque amplification). If GR Input Force = Output Force / MA = 500 N / 4 = 125 N The person needs to apply a force of 125 N. The lever provides a mechanical advantage of 4, making it much easier to lift the heavy rock. 2.2 Transistors as Switches: A transistor is a semiconductor device that can act as an electronic switch or amplifier. In its simplest use, a transistor acts like a switch, controlled by a small current or voltage at the base (for a Bipolar Junction Transistor - BJT) or gate (for a Field Effect Transistor - FET).

NPN Transistor: A small current flowing into the base causes a larger current to flow from the collector to the emitter.

PNP Transistor: A small current flowing out of the base causes a larger current to flow from the emitter to the collector. When the transistor is "on" (saturated), it allows current to flow. When it is "off" (cut-off), it blocks the current flow.