Class 5 | CBSE, NCERT & ICSE
In earlier classes, you learned about 2D (flat) shapes like squares, rectangles, triangles, and circles. These have only length and width β they lie flat on paper. But the real world is 3D! A box, a ball, a tin can, an ice cream cone β these are all 3D shapes (also called solids). They have length, width, AND height (or depth).
A net is what a 3D shape looks like when you "unfold" it flat. Imagine cutting open a cardboard box along its edges and flattening it β that flat pattern is the net of the box. Knowing about nets helps in packaging, gift wrapping, building, and even in space engineering (ISRO folds solar panels flat for launch, then unfolds them in space)!
| Shape | Faces | Edges | Vertices | Real-Life Examples (India) |
|---|---|---|---|---|
| Cube | 6 (all squares) | 12 | 8 | Rubik's cube, dice, sugar cube, Maggi bouillon cube |
| Cuboid | 6 (rectangles) | 12 | 8 | Brick, book, tiffin box, shoe box, phone |
| Cylinder | 3 (2 circles + 1 curved) | 2 | 0 | Water bottle, Bournvita tin, pillar, pipe, rolling pin |
| Cone | 2 (1 circle + 1 curved) | 1 | 1 (apex) | Ice cream cone, party hat, traffic cone, temple gopuram |
| Sphere | 1 (all curved) | 0 | 0 | Cricket ball, globe, ladoo, marble, Earth |
| Triangular Prism | 5 (2 triangles + 3 rectangles) | 9 | 6 | Toblerone box, tent, prism in science lab |
| Square Pyramid | 5 (1 square + 4 triangles) | 8 | 5 | Pyramids of Egypt, roof of a hut |
The Swiss mathematician Leonhard Euler discovered a beautiful relationship between faces, vertices, and edges of any polyhedron (a 3D shape with flat faces):
Faces + Vertices β Edges = 2 (always!)
Let's verify for the shapes we know:
| Shape | F (Faces) | V (Vertices) | E (Edges) | F + V β E |
|---|---|---|---|---|
| Cube | 6 | 8 | 12 | 6 + 8 β 12 = 2 β |
| Cuboid | 6 | 8 | 12 | 6 + 8 β 12 = 2 β |
| Triangular Prism | 5 | 6 | 9 | 5 + 6 β 9 = 2 β |
| Square Pyramid | 5 | 5 | 8 | 5 + 5 β 8 = 2 β |
| Triangular Pyramid (Tetrahedron) | 4 | 4 | 6 | 4 + 4 β 6 = 2 β |
Note: Euler's formula works for all polyhedra (flat-faced 3D shapes). It does NOT work for shapes with curved surfaces (sphere, cylinder, cone) β those are not polyhedra.
A net is a flat 2D pattern that can be folded to make a 3D shape. When you cut a 3D shape along some edges and unfold it, you get its net.
A cube has 6 square faces. Its net is 6 connected squares arranged so they can fold into a cube. There are exactly 11 different nets of a cube!
The most common net looks like a cross (+) with 4 squares in a row and 1 square on each side of the second square.
A cuboid has 6 rectangular faces: 2 each of 3 different sizes (lengthΓwidth, lengthΓheight, widthΓheight). Its net shows all 6 rectangles connected.
Example 1: A cuboid is 5 cm long, 3 cm wide, and 2 cm tall. Describe its net.
Solution: The net will have:
These 6 rectangles are arranged connected along their edges so they fold into the cuboid.
A cylinder unfolds into: 2 circles (top and bottom) + 1 rectangle (the curved surface unfurled). The rectangle's width = height of cylinder, and its length = circumference of the circular base (2Οr).
A cone unfolds into: 1 circle (the base) + 1 sector (fan-shaped piece from the curved surface).
When you look at a 3D object from different directions, you see different 2D shapes. The three standard views are:
| View | Direction | What You See |
|---|---|---|
| Front view | Looking at the object from the front | Height Γ Width (face facing you) |
| Side view | Looking from the left or right side | Height Γ Depth |
| Top view (Plan) | Looking from directly above | Width Γ Depth |
Example 2: What are the front, side, and top views of a cylinder standing upright?
Solution:
Example 3: What are the front, side, and top views of a cone standing on its base?
Solution:
| Word | Meaning |
|---|---|
| 3D Shape / Solid | A shape with length, width, and height (takes up space) |
| Face | A flat (or curved) surface of a 3D shape |
| Edge | A line segment where two faces meet |
| Vertex | A point where three or more edges meet (corner) |
| Net | A 2D pattern that folds into a 3D shape |
| Polyhedron | A 3D shape with all flat faces (no curves) |
| Prism | A 3D shape with two identical parallel ends and rectangular sides |
| Pyramid | A 3D shape with a polygon base and triangular sides meeting at a point |
| Cross-section | The shape you get when you slice through a 3D object |
| Euler's Formula | F + V β E = 2 (for any polyhedron) |
Finished learning? Now test what you know!