Scale and Scale Drawing

Subject: Basic Technology
Class: JSS 3
Term: First Term
Week: 13
Age: 12–15 years
Topic: Scale and Scale Drawing
Sub-topic: Definition, Types, and Practical Scale Drawing
Duration: 60 minutes

Behavioural Objectives

By the end of this lesson, students should be able to:

1. Define scale, enlargement, and reduction.
2. Identify and differentiate between enlargement ratio and reduction ratio.
3. Explain the importance of scale drawings.
4. Create simple scale drawings using appropriate tools.

Keywords

• Scale
• Scale Drawing
• Enlargement
• Reduction
• Ratio
• Dimension

Set Induction

The teacher shows students a map and asks, “Do you think this is the actual size of Lagos? How do you think we can represent large or small objects correctly on paper?” This introduces the idea of scaling objects to fit appropriately on a drawing.

Entry Behaviour

Students are familiar with basic measurements like length and width from previous lessons on dimensioning techniques.

Learning Resources and Materials

• Graph paper, pencils, rulers, and erasers
• Models of objects (e.g., a book, phone)
• Maps or technical drawings for demonstration

Building Background/Connection to Prior Knowledge

Students learned how to represent 3D objects in orthographic views. This lesson builds on those skills by introducing scale drawing, a way to make objects fit proportionally on paper.

Embedded Core Skills

• Critical thinking
• Measurement and scaling
• Problem-solving

Learning Materials

• Graph paper
• Pencils, rulers, protractors, and erasers
• Objects with measurable dimensions

Reference Books

• Lagos State Scheme of Work
• Basic Technology Textbook for Junior Secondary Schools
• “Fundamentals of Technical Drawing” by T. A. Adedayo

Instructional Materials

• Maps, model objects, rulers, graph paper

Content

I. Definition of Scale, Enlargement, and Reduction

• Scale: A proportion used to represent an object’s size on paper, either larger or smaller than the original object.
• Enlargement: Making a drawing larger than the actual object.
• Reduction: Making a drawing smaller than the original object.

II. Types of Scales

1. Enlargement Ratio

• Used when the size of the drawing is larger than the actual object.
• Example: If 1 cm on the drawing represents 0.5 cm in real life, the scale ratio is 2:1.

2. Reduction Ratio

• Used when the drawing is smaller than the original object.
• Example: If 1 cm on the drawing represents 2 cm of the actual object, the scale ratio is 1:2.

III. Scale Drawing

• Scale drawing is the representation of an object or area on paper, where all dimensions are in proportion to the real object.
• Scale drawings are used in:
  • Maps
  • Blueprints
  • House plans
  • Product designs

Steps for Creating a Scale Drawing

1. Measure the original object’s dimensions.
2. Decide the scale to use (e.g., 1:2, 1:5).
3. Convert the measurements using the scale.
4. Draw the object on graph paper using the scaled dimensions.

Examples of Scale Ratios

1. 1:2 – Reduction (1 unit on paper = 2 units in real life)
2. 2:1 – Enlargement (2 units on paper = 1 unit in real life)
3. 1:1 – Full size (actual size representation)
4. 1:50 – Commonly used for architectural plans

Evaluation (Fill-in-the-Blank Questions)

1. A scale of 1:2 represents a __________.
   (a) reduction (b) enlargement (c) full size (d) no change
2. A scale drawing uses a __________ to represent dimensions.
   (a) photograph (b) proportion (c) compass (d) grid
3. When a drawing is smaller than the real object, it is called __________.
   (a) enlargement (b) reduction (c) scaling (d) dimensioning
4. If 2 cm on the drawing equals 1 cm on the object, the ratio is __________.
   (a) 1:2 (b) 2:1 (c) 1:1 (d) 1:5
5. A __________ drawing helps to represent large areas on small paper sizes.
   (a) photograph (b) technical (c) scale (d) 3D
6. Enlargement is represented by a ratio greater than __________.
   (a) 1:2 (b) 1:1 (c) 1:5 (d) 2:1
7. A full-size drawing has a scale ratio of __________.
   (a) 2:1 (b) 1:1 (c) 1:10 (d) 1:5
8. Maps are examples of __________ drawings.
   (a) isometric (b) scale (c) oblique (d) artistic
9. If 1 cm represents 5 cm in real life, the scale is __________.
   (a) 5:1 (b) 1:5 (c) 1:2 (d) 2:1
10. __________ drawings are used for house plans and blueprints.
    (a) Artistic (b) Orthographic (c) Scale (d) Perspective

Class Activity Discussion (FAQs)

1. What is scale drawing?
   It is a way to represent objects proportionally on paper.
2. What is the purpose of using scales?
   To fit large or small objects correctly onto a drawing sheet.
3. What is an example of an enlargement ratio?
   A ratio of 2:1 means the drawing is twice the size of the real object.
4. What is the meaning of 1:50 scale?
   It means 1 unit on the drawing represents 50 units in real life.
5. What tools do you need for scale drawing?
   Graph paper, pencils, rulers, and erasers.
6. What is a reduction ratio?
   A scale where the drawing is smaller than the original object.
7. What scale ratio would you use for a blueprint?
   Ratios like 1:50 or 1:100 are common.
8. Why are scale drawings important?
   They help visualize and plan projects accurately.
9. How do you convert measurements using a scale?
   Multiply or divide the dimensions by the scale ratio.
10. What is the difference between 1:2 and 2:1 scales?
    1:2 is a reduction, while 2:1 is an enlargement.

Teacher’s Activities

1. Explain and demonstrate how to create a scale drawing.
2. Provide students with real objects to measure and draw to scale.
3. Guide students in converting measurements using the selected ratio.

Learners’ Activities

1. Measure an object (e.g., book) and create a scale drawing.
2. Work in pairs to practice using different scale ratios.
3. Present their drawings to the class for peer review and feedback.

Evaluation Questions

1. Define scale drawing.
2. What is the difference between enlargement and reduction?
3. Give an example of an enlargement ratio.
4. Draw a rectangle with a 2:1 enlargement scale.
5. Convert 10 cm to a 1:5 scale drawing.
6. What scale would you use for a house plan?
7. List three examples of where scale drawings are used.
8. How is a map a scale drawing?
9. What is the ratio for a full-size drawing?
10. Draw a simple object with a 1:2 reduction ratio.

Conclusion

The teacher reviews students’ work, providing feedback and ensuring all students understand the concept of scale and how to create accurate scale drawings.