Lesson Notes By Weeks and Term v5 - Grade 7

Lesson Video

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Performance objectives

• Define and calculate mechanical advantage for levers.
• Identify and explain first, second, and third class levers.
• Explain the relationship between effort, load, and fulcrum.
• Apply mechanical advantage to real-world scenarios.

Lesson summary

This week, we delve deeper into the fascinating world of simple mechanisms and how they provide us with mechanical advantage. Understanding these concepts is crucial because simple machines are all around us, making our lives easier. From the wheelbarrow used in gardens to the gears inside a bicycle, simple mechanisms are fundamental to how things work. In South Africa, where many communities rely on manual labor and resourcefulness, a strong understanding of these mechanisms can lead to innovative solutions for everyday challenges and contribute to local entrepreneurship.

Lesson notes

What is a Simple Mechanism? A simple mechanism is a basic device that uses force to do work. They are called “simple” because they usually involve only one movement. They make tasks easier by changing the direction or magnitude of a force. What is Mechanical Advantage (MA)? Mechanical Advantage (MA) is the ratio of the output force (the force you need to lift or move something - the LOAD) to the input force (the force you apply - the EFFORT). It tells us how much a mechanism multiplies your force. A high MA means you can move a heavy load with less effort.

Formula for Mechanical Advantage: MA = Load / Effort Load (L): The force exerted by the object being moved or lifted. This is also sometimes called resistance. Measured in Newtons (N).

Effort (E): The force you apply to the mechanism to move the load. Measured in Newtons (N).

Levers: A Closer Look A lever is a rigid bar that pivots around a fixed point called a fulcrum. Levers are used to multiply force, making it easier to lift or move objects. There are three classes of levers, defined by the relative positions of the fulcrum, load, and effort.

Class 1 Lever: The fulcrum is located between the effort and the load.

Examples include: seesaw, pliers, crowbar. Think of a seesaw. The middle is the fulcrum, one person is the load, and the other person is the effort. MA for a Class 1 lever can be greater than 1, less than 1, or equal to 1, depending on the positions of the effort and load relative to the fulcrum. If the fulcrum is closer to the load, the MA is greater than 1 (easier to lift). If the fulcrum is closer to the effort, the MA is less than 1 (more effort needed, but you might get greater speed or distance).

Class 2 Lever: The load is located between the fulcrum and the effort.

Examples include: wheelbarrow, bottle opener, nutcracker. Think of a wheelbarrow. The wheel is the fulcrum, the load is the materials in the barrow, and you are applying the effort at the handles. The MA for a Class 2 lever is always greater than

1. This means you always gain force advantage.

Class 3 Lever: The effort is located between the fulcrum and the load.

Examples include: tweezers, fishing rod, your forearm (elbow is the fulcrum, muscle provides the effort). Think of your forearm when you lift something. The elbow is the fulcrum, the muscle in your upper arm provides the effort, and the object you’re lifting is the load. The MA for a Class 3 lever is always less than

1. This means you lose force advantage, but you gain speed and range of motion. Calculating Mechanical Advantage for Levers: The mechanical advantage of a lever can be calculated based on the distances from the fulcrum to the effort and the load: MA = Distance from Fulcrum to Effort (Effort Arm) / Distance from Fulcrum to Load (Load Arm)