Mathematics
Grade 7
15 min
Nets of three-dimensional figures
Nets of three-dimensional figures
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1
Introduction & Learning Objectives
Learning Objectives
Define a 'net' in the context of three-dimensional figures.
Identify the three-dimensional figure that a given net will form.
Draw a valid net for common three-dimensional figures like cubes, prisms, and pyramids.
Determine if a given two-dimensional pattern is a valid net for a specific three-dimensional figure.
Relate the faces, edges, and vertices of a three-dimensional figure to its corresponding net.
Visualize how a two-dimensional net folds into a three-dimensional shape.
Have you ever flattened a cardboard box? 📦 That flattened shape is a 'net' of the box! What other everyday objects can you 'unfold'?
In this lesson, we'll explore nets, which are two-dimensional patterns that can be folded to form three-dimensio...
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Key Concepts & Vocabulary
TermDefinitionExample
NetA net is a two-dimensional (flat) pattern that can be folded along its edges to form a three-dimensional (3D) figure.The unfolded pattern of a cereal box is a net of a rectangular prism.
Three-Dimensional (3D) FigureA figure that has length, width, and height (or depth). It occupies space.A cube, a pyramid, a cylinder, and a sphere are all 3D figures.
FaceA flat surface of a three-dimensional figure. In a net, these are the individual shapes (like squares, triangles, rectangles) that make up the pattern.A cube has 6 square faces. In its net, you'll see 6 squares.
EdgeA line segment where two faces of a three-dimensional figure meet. In a net, these are the lines along which the net is folded.A cube has 12 edges. When you fold a net of a cube, these lines beco...
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Core Formulas
Net Validity Principle
A pattern is a valid net if and only if it can be folded along its edges to form a specific three-dimensional figure without any overlaps or gaps.
This rule helps you check if a given 2D pattern will actually create a 3D shape. Imagine cutting it out and folding it. If it forms the shape perfectly, it's a valid net.
Face Correspondence Rule
The number of faces in a net must exactly match the number of faces of the three-dimensional figure it represents. \text{Number of faces in net} = \text{Number of faces in 3D figure}
Before folding, count the individual shapes (faces) in the net. This count must be equal to the total number of faces on the 3D figure you expect to form. For example, a cube has 6 faces, so its net must have 6 squares.
Edge Al...
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Challenging
A net for a rectangular prism is made of six rectangles. The areas of three of the faces are 10 cm², 12 cm², and 30 cm². If each of these is a unique face pair (front/back, top/bottom, left/right), what are the dimensions (length, width, height) of the prism?
A.1cm, 10cm, 12cm
B.2cm, 5cm, 6cm
C.3cm, 4cm, 10cm
D.1cm, 12cm, 30cm
Challenging
You have a row of four squares. To make it a valid net for a cube, you need to add two more squares. Which of the following placement rules will ALWAYS result in a valid net?
A.Place both squares on the same side of the row.
B.Place both squares at one end of the row.
C.Place one square on one side of the row, and the second square on the same side but further down the row.
D.Place one square on one side of the row, and the second square on the opposite side of the row, but not on the end squares.
Challenging
A net is constructed from one regular pentagon and five congruent isosceles triangles, with the base of each triangle matching a side of the pentagon. To form a valid pentagonal pyramid, what must be true about the side length 's' of the triangles (the two equal sides)?
A.The side length 's' does not matter.
B.The side length 's' must be shorter than the pentagon's side length.
C.The side length 's' must be long enough for the triangle vertices to meet at a single point (apex) above the center of the base.
D.The side length 's' must be exactly equal to the pentagon's side length.
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