Kelas 8 - Bab 8 (Part 1) - Kubus dan Balok

Introduction

In this tutorial, we will explore the concepts of cubes and rectangular prisms (balok) as presented in the Kelas 8 mathematics curriculum. Understanding these geometric shapes is essential for calculating their surface area and volume, which are fundamental skills in geometry. This guide will break down the key components, formulas, and methods necessary to work with cubes and rectangular prisms.

Step 1: Understanding the Elements of Cubes and Rectangular Prisms

• Cubes:

  • A cube is a three-dimensional shape with six equal square faces.
  • Each face has equal dimensions.
  • Important characteristics include:
    • Edge: The length of one side of the cube.
    • Vertex: A point where the edges meet (there are 8 vertices in a cube).
    • Face: A flat surface of the cube (there are 6 faces).

• Rectangular Prisms:

  • A rectangular prism has six rectangular faces, opposite faces are equal.
  • Important characteristics include:
    • Length (l): The longer side of the rectangle.
    • Width (w): The shorter side of the rectangle.
    • Height (h): The depth of the prism.

Step 2: Calculating the Surface Area of Cubes and Rectangular Prisms

• Surface Area of a Cube:

  • The formula to calculate the surface area (SA) is:

    SA = 6 * (edge length)^2
    

  • Example: If the edge length is 4 cm, then:

    SA = 6 * (4 cm)^2 = 6 * 16 cm² = 96 cm²
    

• Surface Area of a Rectangular Prism:

  • The formula is:

    SA = 2 * (l * w + l * h + w * h)
    

  • Example: If length = 5 cm, width = 3 cm, and height = 4 cm, then:

    SA = 2 * (5 cm * 3 cm + 5 cm * 4 cm + 3 cm * 4 cm) 
    = 2 * (15 cm² + 20 cm² + 12 cm²) 
    = 2 * 47 cm² 
    = 94 cm²
    

Step 3: Calculating the Volume of Cubes and Rectangular Prisms

• Volume of a Cube:

  • The formula for volume (V) is:

    V = (edge length)^3
    

  • Example: If the edge length is 4 cm, then:

    V = (4 cm)^3 = 64 cm³
    

• Volume of a Rectangular Prism:

  • The formula is:

    V = length * width * height
    

  • Example: If length = 5 cm, width = 3 cm, and height = 4 cm, then:

    V = 5 cm * 3 cm * 4 cm = 60 cm³
    

Conclusion

In this guide, we covered the essential aspects of cubes and rectangular prisms, including their definitions, characteristics, surface area, and volume calculations. Understanding these concepts is not only crucial for academic success but also for practical applications in real-world scenarios such as architecture, packaging, and manufacturing. As a next step, practice solving problems involving these shapes to solidify your understanding and improve your skills.