BAB 3: USAHA, ENERGI DAN PESAWAT SEDERHANA | Part 3: PESAWAT SEDERHANA | IPA Kls 8 Kurikulum Merdeka

Introduction to Simple Machines
📌 Simple machines are tools used by humans to simplify work or effort, such as wheelbarrows, inclined planes (ramps), and pulley systems for drawing water from wells.
⚙️ Simple machines function by increasing the lifting force, increasing the distance over which the force is applied, or changing the direction of the force.
🛠️ The main types of simple machines discussed are pulleys (katrol), wheels (roda), inclined planes (bidang miring), and levers (tuas).

Pulleys (Katrol)
🔗 Mechanical Advantage ($\text{KM}$) is the factor by which a simple machine multiplies the force, calculated as $\text{KM} = \text{F}_{b} / \text{F}_{k}$ (Load Force / Effort Force).
⚫ Fixed Pulley (Katrol Tetap): The axis is stationary; $\text{KM} = 1$, only changing the direction of the force (e.g., well drawing, flagpole).
〰️ Movable Pulley (Katrol Bebas): The axis moves freely; the effort force is half the load force, resulting in $\text{KM} = 2$ (e.g., container lifting at ports).
🔀 Compound Pulley (Katrol Majemuk): A combination of fixed and movable pulleys; $\text{KM}$ equals the total number of ropes supporting the load. (Example calculation showed $\text{KM}=4$ with 4 pulleys, requiring $8 \text{N}$ effort to lift a $32 \text{N}$ load).

Inclined Plane (Bidang Miring)
📏 An inclined plane is a slanted surface used to move heavy loads by covering a greater distance with less required force.
📉 The force needed decreases as the slope becomes less steep (more gentle), and increases as it becomes steeper.
📐 $\text{KM}$ for an inclined plane is calculated as $\text{KM} = \text{L} / \text{H}$ (Length of the plane / Height). (Example showed a ramp $8\text{m}$ long and $4\text{m}$ high yields $\text{KM}=2$).
⛰️ Applications include mountain roads built windingly and screws.

Wheel and Axle (Roda Berporos)
🎡 This machine uses a wheel connected to a central axle that rotates together, minimizing friction to move objects.
📏 The Mechanical Advantage ($\text{KM}$) is determined by the ratio of the radii: $\text{KM} = \text{Radius}_{\text{wheel}} / \text{Radius}_{\text{axle}}$.

Lever (Pengungkit/Tuas)
🦴 Levers are rigid bars used for lifting or prying, classified into three types based on the relative positions of the fulcrum ($\text{Tumpu}$), load ($\text{Beban}$), and effort ($\text{Kuasa}$).
1️⃣ First-Class Lever: Fulcrum is located between the effort and the load. (Example: Head/neck movement, where the skull is the fulcrum).
2️⃣ Second-Class Lever: Load is located between the fulcrum and the effort. (Example: Foot sole, where the leg bone is the load location).
3️⃣ Third-Class Lever: Effort is located between the fulcrum and the load. (Example: Arm movement, where the elbow is the fulcrum).

Key Points & Insights
➡️ Simple machines are categorized into four main types: pulley, wheel, inclined plane, and lever.
➡️ Understanding $\text{KM}$ is crucial; for fixed pulleys $\text{KM}=1$, while for movable pulleys $\text{KM}=2$.
➡️ In levers, the classification depends entirely on the central placement of the fulcrum, load, or effort.

📸 Video summarized with SummaryTube.com on Nov 23, 2025, 12:48 UTC