Liberia - Grade 4 - Mathematics

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Subject: Mathematics

Semester: 2

Period: 6

Week: 33

School Name:
Teacher’s Name:
Subject: Mathematics
Grade Level: Grade 4
Date: Week 33
Lesson Duration: 45 minutes
Week & Period: Week 33, Period 6
Topic: Circles
Sub-topic: Definition and Parts of a Circle

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

Define a circle.
Identify and label parts of a circle.
Explain the relationship between radius and diameter.

Previous Knowledge
Students already know how to recognize round objects like coins and plates.

Instructional Materials
Mathematics textbook for Grade 4, cardboard circles, compasses, protractors, chalkboard.

Lesson Development – ABC Model
A – Anticipation (Warm-up / Starter)
Time: 5–10 minutes
Teacher shows a coin and asks: “What shape is this?”

B – Building Knowledge (Main Lesson Body)

Time: 25–30 minutes

🧠 Key Definition

A circle is a 2D closed shape where every point on the edge is the same distance from a fixed point called the center.

✅ A circle is not made of straight lines, and it has no corners or sides.

🎯 Parts of a Circle (with Definitions)

Part	Definition	Notation / Example
Center	The fixed point in the middle of the circle. All points on the circle are the same distance from it.	Labeled as point O (or any letter)
Radius (r)	A line from the center to any point on the circle. All radii in a circle are equal in length.	If center is O and point A is on circle → OA = radius
Diameter (d)	A straight line that goes from one side of the circle to the other, passing through the center. It is the longest chord in a circle.	If A and B are on the circle and O is center → AB = diameter
Chord	A line that connects any two points on the circle. Does not have to pass through center.	If P and Q are points on the circle → PQ = chord
Arc	A part or section of the circle's curve.	A curved portion between two points on the circle.
Circumference	The total distance around the circle. It’s like the "perimeter" of a circle.	Measured in cm or m, depending on the circle size.

📐 Important Relationship

✅ The diameter is always twice the radius.

🧮 Formula:

Diameter=2×Radiusord=2r

Radius=Diameter/2 r=d/2

📊 Examples

Given	Find	Solution
Radius = 5 cm	Diameter = ?	2 × 5 = 10 cm
Diameter = 12 cm	Radius = ?	12 ÷ 2 = 6 cm
Center = O; Point A on circle	Radius = OA	Measure OA with ruler

🧍‍♀️ Learners’ Activities (Expanded)

🔸 1. Circle Tracing & Labeling

Use compasses or circular objects (cups, bottle caps) to trace circles on paper.
Label:

Center (O)
Radius (e.g., OA)
Diameter (e.g., AB through O)
Chord (not through center, e.g., CD)
Arc (curved part between two points)
Circumference (entire edge)

🔸 2. Folding Circles

Give students paper circles.
Activity steps:

Fold once through the center: shows the diameter.
Mark the center point (where the folds cross).
Fold again from center to edge: shows the radius.
Use scissors to cut an arc.

🔸 3. Real-World Measurements

Students bring or use circular objects:

Bottle cap, plate, cup base

Measure:

Diameter with a ruler
Estimate the radius
Discuss the difference between chord and diameter

🔸 4. Group Sorting Activity

Provide cutouts or images of different lines on a circle.
Learners sort and label:

Radius
Diameter
Chord
Arc

✅ Assessment Checks (Formative Questions)

🔸 Oral / Quick Response

"What do we call the middle of a circle?"
➤ Center
"If the radius is 6 cm, what is the diameter?"
➤ 12 cm
"True or False: A chord must pass through the center."
➤ False
"Name the longest straight line in a circle."
➤ Diameter

🔸 Written / Exit Ticket

Draw and label the following parts of a circle:
- Center, radius, diameter, chord, arc
Fill in the blanks:
- Radius = 7 cm → Diameter = ___ cm
  ➤ 14 cm
- Diameter = 20 cm → Radius = ___ cm
  ➤ 10 cm
Match the Part to Its Description:

Part	Description
Radius	A. Line connecting any two points on circle
Diameter	B. Half the diameter
Chord	C. Goes through center and touches two sides
Arc	D. A part of the circumference

Answers:

Radius → B
Diameter → C
Chord → A
Arc → D

🧑‍🏫 Teacher Notes (Expanded & Detailed)

✏️ Key Teaching Points:

Reinforce that radius and diameter are related (d = 2r).
Use accurate vocabulary consistently:

Students should say “diameter” instead of “line across”
“Arc” instead of “curve”

🧩 Common Misconceptions:

Chord always passes through center → ❌ Not always (only diameter does)
Radius and diameter are unrelated → ❌ Correct this with examples and measurements

🧠 Differentiation:

For advanced learners: Introduce basic formula for circumference (C = πd or C = 2πr)
For struggling learners: Use physical models and visual aids more heavily

📘 Optional Homework / Extension

"Circle Investigator" Worksheet

Measure the diameter of 3 circular objects at home
Calculate the radius
Draw one of the circles and label its parts

Craft Extension

Cut and decorate a paper circle
Use yarn or ribbon to show the radius and diameter
Label parts clearly

C – Consolidation (Conclusion & Assessment)
Time: 5–10 minutes
Summary: A circle has special parts, and the diameter is always twice the radius.

Evaluation Method (Expanded)
Exit slip/quiz: Label 4 parts of a circle on a diagram.

Assignment (Expanded)
Draw 2 circles, measure their radii and calculate their diameters.

Follow-up Activity
Students will measure round household objects and find radius and diameter.

Differentiation / Inclusive Strategies
Give larger circle templates for learners who struggle with compass use. Pair students in group work.

Teacher’s Reflection (After Class)
What worked well? ___________________________________________
What needs improvement? ____________________________________
Students’ engagement level: ☑ High ☑ Medium ☑ Low