Circles in Technical Drawing: Understanding Parts, Properties, and Applications Technical Drawing SS 1 First Term Lesson Notes Week 8

Technical Drawing, SS 1, First Term, Week 8 on Circles.

Lesson Plan: Circles

Subject: Technical Drawing
Class: SS 1
Term: First Term
Week: 8
Age: 14-16 years
Topic: Circles
Sub-Topic: Types, Parts, and Division of Circles
Duration: 40 minutes

Behavioral Objectives

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

1. Mention and identify different types of circles.
2. Identify the various parts and properties of a circle.
3. Divide a circle into a number of equal parts.
4. Recognize objects around them that have a circular shape.

Keywords

• Circle
• Radius
• Diameter
• Circumference
• Arc
• Sector
• Equal division

Set Induction

The teacher will display common objects like coins, wheels, and plates, asking students to describe their shapes and identify them as examples of circles.

Entry Behavior

Students have basic knowledge of lines and angles from previous lessons.

Learning Resources and Materials

• Compass
• Rulers
• Protractors
• Circular objects (coins, CDs, etc.)
• Drawing sheets

Building Background/Connection to Prior Knowledge

Students have studied lines and angles, which are fundamental for understanding circles and circular shapes in technical drawing.

Embedded Core Skills

• Observation and identification
• Practical application of geometric principles
• Spatial reasoning
• Measurement and division

Learning Materials

• Lagos State Scheme of Work for Technical Drawing
• Illustrated diagrams of different types of circles and their parts

Reference

• Lagos State Scheme of Work
• “Technical Drawing and Engineering Graphics” by A. Bankole

Instructional Materials

• Visual charts showing types and parts of a circle
• Drawing instruments for circle constructions
• Samples of divided circles

Content Outline

1. Types of Circles:
   • Description of common types: concentric, tangent, and overlapping circles.
2. Parts of a Circle:
   • Definitions and identification of radius, diameter, circumference, chord, arc, sector, and segment.
3. Properties of a Circle:
   • Explanation of basic properties, such as all points being equidistant from the center.
4. Division of a Circle:
   • Techniques for dividing a circle into equal parts using a protractor and compass.
5. Circular Objects Around Us:
   • Real-life examples of objects with circular shapes (e.g., clocks, car wheels).

Fill-in-the-Blank Questions

1. The longest chord in a circle is called the ______ (a. radius, b. diameter, c. circumference, d. arc).
2. A ______ is a line from the center to the edge of a circle (a. radius, b. diameter, c. chord, d. sector).
3. The ______ of a circle is the distance around it (a. area, b. circumference, c. radius, d. arc).
4. A ______ is a portion of a circle’s circumference (a. segment, b. sector, c. arc, d. tangent).
5. Dividing a circle into 4 equal parts creates ______ (a. quadrants, b. octants, c. segments, d. arcs).
6. The distance from one edge of a circle to another, passing through the center, is called the ______ (a. radius, b. diameter, c. chord, d. tangent).
7. ______ circles share the same center point (a. Overlapping, b. Tangent, c. Concentric, d. Perpendicular).
8. The area within a circle between two radii is called a ______ (a. chord, b. sector, c. segment, d. arc).
9. ______ are commonly used to divide circles into equal parts (a. Compasses, b. Set squares, c. Rulers, d. Erasers).
10. Circular shapes are used in designing objects like ______ (a. squares, b. rectangles, c. wheels, d. triangles).

FAQ

1. What is the radius of a circle?
   • The radius is the distance from the center of the circle to any point on its edge.
2. How is the diameter related to the radius?
   • The diameter is twice the length of the radius.
3. What is the circumference?
   • The circumference is the distance around the outside of the circle.
4. Can a circle be divided into equal parts?
   • Yes, circles can be divided into any number of equal parts, commonly by using a compass and protractor.
5. What are some objects around us that are circular?
   • Examples include car wheels, clocks, plates, and coins.

Circles

• Mention and Identify Different Types of Circles:
  • Explanation: There are various types of circles, each with unique properties or uses in technical drawing and geometry. Understanding these types helps students in classifying and working with different circular shapes.
  • Types of Circles:
    • Concentric Circles: Circles with a common center but different radii.
      • Example: The rings of a target.
    • Eccentric Circles: Circles that do not share the same center but are positioned closely.
      • Example: Gears or pulleys with slightly offset centers.
    • Tangent Circles: Circles that touch at exactly one point.
      • Example: Two wheels that barely touch each other.
  • Why it’s Important: Recognizing these different circle types is essential in technical drawing and design for applications like creating patterns, mechanical parts, or decorative designs.
• Identify Various Parts and Properties of a Circle:
  • Explanation: Knowing the parts of a circle and their properties helps in understanding and working with circular shapes in technical drawings. Each part has a unique role in defining a circle’s shape and measurement.
  • Parts of a Circle:
    • Radius: The distance from the center of the circle to any point on its circumference.
      • Property: All radii of a circle are equal in length.
    • Diameter: A line that passes through the center, connecting two points on the circumference. It’s twice the length of the radius.
    • Circumference: The total distance around the circle.
      • Property: Calculated as $2\pi r$ or $\pi d$, where $r$ is the radius and $d$ is the diameter.
    • Chord: A line segment connecting two points on the circumference without passing through the center.
    • Arc: A curved segment of the circumference.
    • Sector: A “slice” of the circle, created by two radii and the arc between them.
  • Why it’s Important: Identifying these parts helps students accurately measure, divide, and work with circles in various drawings and projects.
• Divide a Circle into a Number of Equal Parts:
  • Explanation: Dividing a circle into equal parts is a common skill in technical drawing, useful for creating evenly spaced patterns, designs, and rotational symmetry.
  • Steps to Divide a Circle:
    • Draw a circle and mark its center.
    • Use a protractor or compass to divide the circle into equal angles (e.g., 4, 6, or 8 parts).
    • Draw lines from the center to each point to divide the circle.
  • Why it’s Important: Dividing circles into equal parts is necessary in design work, such as creating pie charts, gears, or architectural elements that require rotational symmetry.
• Recognize Objects that are Circular Around Them:
  • Explanation: Recognizing circular objects in everyday life helps students connect geometric concepts to real-world applications.
  • Examples of Circular Objects:
    • Wheels: Circular for smooth and continuous rolling.
    • Clocks: Often circular, representing time in a round display.
    • Plates: Round shape allows for easy rotation and handling.
    • Cylinders (e.g., cans): Circular at the top and bottom for stability.
  • Why it’s Important: Identifying circular objects in their surroundings helps students appreciate the practical use of circles and improves spatial awareness.

Presentation Steps

Step 1: Revision of Previous Topic
The teacher will review the previous lesson on line division to reinforce students’ understanding of dividing and measuring lines.

Step 2: Introduction of New Topic
The teacher introduces circles, describing their importance in everyday life and engineering designs.

Step 3: Student Contributions and Corrections
Students will attempt to draw and label parts of a circle on their drawing sheets. The teacher will check for accuracy and make corrections.

Teacher’s Activities

• Demonstrate drawing a circle using a compass.
• Show how to identify and label parts of a circle (radius, diameter, circumference).
• Guide students in dividing a circle into equal parts using a protractor.

Learner’s Activities

• Practice drawing circles and marking parts such as the radius, diameter, and center.
• Attempt to divide their circles into equal segments under teacher supervision.
• Discuss and identify circular objects they encounter in daily life.

Assessment

• The teacher will assess students’ ability to draw, label, and divide a circle accurately.
• Observation of students’ understanding of circular parts and properties.

Evaluation Questions

1. Name three parts of a circle.
2. What is the radius of a circle?
3. How do you define the diameter?
4. Why is the circumference important?
5. How can you divide a circle into equal parts?

Conclusion

The teacher will conclude by emphasizing the importance of understanding circles in technical drawing and their applications in real life.