Lesson 8: Solid Objects and Plane Shapes

For Grade 3 Mathematics

Lesson Objective:

Students will be able to identify and differentiate between solid objects (3D shapes) and plane shapes (2D shapes), and recognize plane shapes as faces of solid objects. They will also understand basic properties of these shapes.

Understanding Solid Objects (3D Shapes):

Solid objects are three-dimensional (3D) shapes that have length, width, and height. They take up space and you can hold them. They have **faces** (flat surfaces), **edges** (where two faces meet), and **vertices** (corners where edges meet). Common solid objects include:

Examples:

  • **Cube:** Like a dice or an ice cube. It has 6 square faces, 12 edges, and 8 vertices.
  • **Cuboid:** Like a brick or a shoebox. It has 6 rectangular (and sometimes square) faces, 12 edges, and 8 vertices.
  • **Cylinder:** Like a can of soup or a drum. Has 2 circular faces and 1 curved surface, 2 edges (where circular faces meet curved surface), and no vertices.
  • **Cone:** Like an ice cream cone or a party hat. Has 1 circular face and 1 curved surface leading to a point (apex). It has 1 edge and 1 vertex.
  • **Sphere:** Like a ball or a globe. It's perfectly round with no flat faces, no edges, and no vertices.

Understanding Plane Shapes (2D Shapes):

Plane shapes are two-dimensional (2D) shapes that only have length and width, but no thickness. They are flat. They have **sides** (straight lines that form the shape) and **vertices** (corners where sides meet). Common plane shapes include:

Examples:

  • **Square:** Has 4 equal sides and 4 vertices. All angles are right angles.
  • **Rectangle:** Has 4 sides (opposite sides are equal) and 4 vertices. All angles are right angles.
  • **Triangle:** Has 3 sides and 3 vertices.
  • **Circle:** A perfectly round shape with no straight sides and no vertices.

Relationship between Solid Objects and Plane Shapes:

The flat surfaces of solid objects are called **faces**, and these faces are plane shapes! When you trace around a face of a solid object, you get a plane shape.

Examples:

  • A cube has faces that are **squares**.
  • A cuboid has faces that are **rectangles** (and sometimes squares).
  • A cylinder has two faces that are **circles**.
  • A cone has one face that is a **circle**.

Activity 1: Identify the Face!

What 2D shape is a face of the following solid object?

Activity 2: Match the Faces!

Which 2D shape is a face of the given solid object?

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