Lesson Notes By Weeks and Term v3 - Primary 3
Length I
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Length I
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Subject: General Mathematics
Class: Primary 3
Term: 1st Term
Week: 7
Theme: Mensuration And Geometry
This page supports the lesson note with a companion video and a short classroom-ready summary.
For class groups and homework, share this lesson page so learners also get the summary, objectives, and full lesson context.
Watch on YouTubemeasure the length and/or width of room, table, building and straight edged materials, etc.; mention importance/benefits of standard units of measurement; find perimeters of regular figures in metres and centimeters by measurement; identify perimeter of regular shapes in the ir environment;
(The teacher should also guide students to convert this to metres if applicable, e.g., 0.6 m, but for Primary 3, 60 cm is sufficient). 2.
4. Perimeter of Regular Figures (Objective 3 & 4) The perimeter of a two-dimensional shape is the total distance around its boundary or outline. It is found by adding the lengths of all its sides. The term "regular figures" implies shapes with straight edges like squares, rectangles, and triangles.
Identifying Perimeter (Objective 4): Rectangle: A shape with four straight sides where opposite sides are equal in length and all angles are right angles.
Examples: blackboard, window pane, door.
Square: A special type of rectangle where all four sides are equal in length.
Examples: floor tile, face of a dice.
Triangle: A shape with three straight sides.
Examples: a section of a roof, a road sign. Finding Perimeter by Measurement (Objective 3): To find the perimeter, learners must physically measure each side of the figure and then add these measurements together.
Worked Example 3: Finding the Perimeter of a Rectangular Table Top Task: Find the perimeter of a rectangular classroom table top.
Tools: Tape measure.
Shape: Rectangle.
Steps:
1. Measure Length 1 (L1): Use the tape measure to find the length of one long side. Let's say it's 120 cm.
2. Measure Length 2 (L2): Measure the opposite long side. It should also be 120 cm.
3. Measure Width 1 (W1): Measure one short side. Let's say it's 60 cm.
4. Measure Width 2 (W2): Measure the opposite short side. It should also be 60 cm.
5. Add all sides: Perimeter = L1 + L2 + W1 + W2 Perimeter = 120 cm + 120 cm + 60 cm + 60 cm Perimeter = 360 cm Conversion (Optional but good for exposure): Since 100 cm = 1 m, then 360 cm = 3 metres and 60 centimetres (or 3.6 m). For Primary 3, expressing it as 360 cm is acceptable, or 3m 60cm.
Worked Example 4: Finding the Perimeter of a Square Floor Tile Task: Find the perimeter of a square floor tile in the classroom.
Tools: Ruler or tape measure.
Shape: Square (all four sides are equal).
Steps:
1. Measure one side: Since all sides are equal, measuring just one side is enough. Let's say the side length (S) is 30 cm.
2. Add all sides: Perimeter = S + S + S + S Perimeter = 30 cm + 30 cm + 30 cm + 30 cm Perimeter = 120 cm Alternatively: Perimeter = 4 × S = 4 × 30 cm = 120 cm.
Conversion: 120 cm = 1 metre and 20 centimetres (or 1.2 m). This section provides the essential knowledge and methodologies for the teacher to deliver the lesson effectively. 2.
1. Concept of Length Length is the measurement of how long something is or the distance between two points. It quantifies extent along a straight line. For instance, the length of a table is how far it stretches from one end to the other, while its width is how broad it is. 2.
2. Non-Standard Units of Measurement Historically, and sometimes informally, people used parts of their body or common objects to measure length. These are called non-standard units.
Hand Span: The distance from the tip of the thumb to the tip of the little finger when the hand is fully stretched.
Foot Span: The length of one's foot.
Cubit: The distance from the elbow to the tip of the middle finger.
Pace/Stride: The length of a step. Why Non-Standard Units are Problematic (Importance of Objective 2): The major drawback of non-standard units is their inconsistency. Different people have different hand spans, foot spans, or cubits. If two people measure the same object using their hand spans, they are likely to get different values, leading to confusion and errors, especially in activities like building or tailoring. This highlights the need for standard units. 2.
3. Standard Units of Measurement (Metre and Centimetre) To ensure consistency and accuracy globally, standard units of measurement have been adopted. For length, the basic standard unit in the International System of Units (SI) is the metre.
Metre (m): The primary unit of length for measuring objects of moderate size, like the length of a classroom, a car, or a tall person.
Centimetre (cm): A smaller unit, useful for measuring shorter lengths, such as the length of a pencil, an exercise book, or a finger. There are 100 centimetres in 1 metre.
Relationship: 1 metre (m) = 100 centimetres (cm). This conversion is essential.
Measuring Tools: Ruler: Typically 30 cm long, used for measuring shorter lengths. It has markings for centimetres and millimetres (though millimetres are usually introduced later).
Tape Measure: Can be much longer (e.g., 1m, 5m, 10m, 50m), made of flexible material, used for measuring longer or curved distances, and is essential in tailoring, carpentry, and construction.
How to Measure with Standard Tools:
1. Placement: Place the measuring tool (ruler or tape measure) along the object to be measured, ensuring the 'zero' mark of the tool aligns with one end of the object.
2. Reading: Read the mark on the tool that aligns with the other end of the object.
3. Units: Always state the unit of measurement (cm or m).
Worked Example 1: Measuring an Exercise Book Task: Measure the length of a Primary 3 General Mathematics exercise book.
Tool: A 30 cm ruler.
Steps:
1. Place the ruler along the longest side of the exercise book, aligning the '0' mark with one corner.
2. Observe where the other end of the book reaches on the ruler.
3. If it reaches the '28' mark, the length of the book is 28 cm.
Measurement: Length = 28 cm.
Worked Example 2: Measuring the Width of a Classroom Table Task: Measure the width of a standard classroom table.
Tool: A tape measure (e.g., 2m long).
Steps:
1. Place the tape measure across the width of the table, aligning the '0' mark with one edge.
2. Stretch the tape measure straight to the opposite edge.
3. Read the measurement where the tape meets the edge. If it reads 60 cm.
Measurement: Width = 60 cm. (The teacher should also guide students to convert this to metres if applicable, e.g., 0.6 m, but for Primary 3, 60 cm is sufficient). 2.
4. Perimeter of Regular Figures (Objective 3 & 4) The perimeter of a two-dimensional shape is the total distance around its boundary or outline. It is found by adding the lengths of all its sides. The term "regular figures" implies shapes with straight edges like squares, rectangles, and triangles.
Identifying Perimeter (Objective 4): Rectangle: A shape with four straight sides where opposite sides are equal in length This section outlines practical, step-by-step activities for both the teacher and learners to achieve the lesson objectives. 3.
1. Introduction (10 minutes)
Teacher Activity: Begin by asking learners how they would compare the length of two different objects (e.g., two pencils of different sizes). Guide them to understand that they can visually compare. Then, ask how they would accurately know how much longer one pencil is than the other, or how to measure the length of the classroom. Introduce the term "length" as the measure of how long something is. Introduce non-standard units (hand span, foot span) and conduct a quick demo.
Learner Activity: Participate in Q&A sessions. Volunteer to compare lengths of objects. Watch the teacher's demonstration of non-standard units. 3.
2. Exploring Non-Standard Units and Their Limitations (15 minutes) - (Objective 2 Focus)
Teacher Activity: Divide the class into small groups (e.g., 4-5 learners per group). Instruct each group to measure the length of their classroom table using their hand spans. Ask groups to record their measurements. Facilitate a class discussion, comparing the different measurements obtained by different groups for the same table. Lead them to conclude that hand spans give different results because people's hands are different sizes. Emphasise the problem of inconsistency in trading goods or building structures with non-standard units.
Learner Activity: In groups, measure the length of their table using hand spans. Record their measurements. Share their results with the class. Engage in the discussion about why results differ and the need for a common way to measure. 3.
3. Introduction to Standard Units and Measuring Tools (20 minutes) - (Objective 1 Focus)
Teacher Activity: Introduce standard units: centimetre (cm) and metre (m).
Explain the relationship: 1 m = 100 cm. Show real rulers (30 cm) and tape measures (longer, flexible). Demonstrate how to correctly use a ruler to measure a short object (e.g., a pencil, an eraser), ensuring the '0' mark is aligned. Demonstrate how to use a tape measure for longer objects (e.g., the teacher's desk, the width of a door). Emphasise reading the scale and stating the unit (cm or m).
Learner Activity: Observe the teacher's demonstration carefully. Handle rulers and tape measures (if available) under supervision. Practice aligning the '0' mark. Identify cm and m markings on the tools. 3.
4. Practical Measurement Activity with Standard Units (30 minutes) - (Objective 1 Focus)
Teacher Activity: Provide each group with rulers and a tape measure (or share among groups). List specific objects for each group to measure (e.g., "Group A: Measure the length of a textbook, width of the classroom door.
Group B: Measure the length of the teacher's table, height of a window.
Group C: Measure the length of a piece of chalk, width of the blackboard."). Circulate among groups, providing guidance, checking techniques, and correcting errors. Ensure learners record their measurements, stating the units.
Learner Activity: In their groups, take turns measuring the assigned objects using rulers and tape measures. Practise aligning the tool, reading the scale, and recording measurements. Collaborate and assist each other in measuring. 3.
5. Introducing Perimeter and Identifying Shapes (20 minutes) - (Objective 4 Focus)
Teacher Activity: Walk around the classroom, pointing to regular shapes: "Look at the blackboard. What shape is it?" (Rectangle) "If I want to put a border all around this blackboard, what part of the blackboard am I measuring?" (The edges/outline). Introduce the term "perimeter" as the distance around a shape. Point out other shapes in the environment (e.g., window, door, floor mat, classroom wall) and ask learners to identify them and imagine walking around their edges. Discuss real-life examples in Nigeria where knowing perimeter is useful (e.g., fencing a compound, framing a picture).
Learner Activity: Identify different regular shapes in the classroom. Participate in discussions about "distance around" and its use. * Trace the perimeter of objects with their fingers or eyes. *3.
6. Finding (The edges/outline). Introduce the term "perimeter" as the distance around a shape. Point out other shapes in the environment (e.g., window, door, floor mat, classroom wall) and ask learners to identify them and imagine walking around their edges. Discuss real-life examples in Nigeria where knowing perimeter is useful (e.g., fencing a compound, framing a picture).
Learner Activity: Identify different regular shapes in the classroom. Participate in discussions about "distance around" and its use. Trace the perimeter of objects with their fingers or eyes. 3.
6. Finding Perimeter by Measurement (30 minutes) - (Objective 3 Focus)
Teacher Activity: Assign each group a large, accessible regular figure in the classroom or outside (e.g., a rectangular mat, a square marked on the floor, the top of a large table). Instruct learners to first identify the shape and then measure each of its sides using tape measures (or rulers for smaller objects). Guide them to record each side's measurement. Instruct them to add all the side measurements to find the perimeter. Supervise and assist as they measure and calculate. Review calculations and reinforce unit consistency (cm + cm + cm = cm).
Learner Activity: In groups, choose an assigned shape. Measure each side of the shape carefully using standard units. Record each side's length. Calculate the perimeter by adding all the measured side lengths. Present their findings to the class. 3.
7. Conclusion and Recap (5 minutes)
Teacher Activity: Quickly review the concepts of length, standard units (cm, m), the importance of standard units, and perimeter. Ask quick questions to check understanding.
Learner Activity: Respond to review questions. Summarise key takeaways.
Understanding length and perimeter has numerous practical applications in everyday Nigerian life, integrating with various aspects of community, economy, and environment.
Home and Household Management: Furniture Arrangement: When arranging furniture (e.g., beds, tables, cupboards) in a room, knowing the length and width of the room and the furniture helps ensure everything fits properly. For example, a family moving into a new mud house in a rural area needs to measure the room to decide where to place their mat, bed, or cooking stove.
Buying Materials: When purchasing materials like fabric for curtains or mats, knowing the exact length required (measured in metres or centimetres) prevents wastage or shortage. A mother buying Ankara fabric at the market needs to specify the exact number of metres for her wrapper or a child's dress.
Trade and Commerce in Markets: Selling Goods by Length: Many items in Nigerian markets are sold by length, such as ropes, electrical cables, textile fabrics, or even some food items like sugarcane. Traders and customers rely on standard units (metres) for fair transactions. Without standard units, disputes would be common.
Packaging: Measuring the perimeter of a package or container can help determine the length of string or tape needed to secure it, a common practice for market vendors packaging goods.
Agriculture and Community Development: Farm Plot Measurement: Farmers often need to measure the perimeter of their small farm plots, especially when planning to erect fences to protect crops from animals or to divide land. For instance, a farmer in Benue State planning to fence a yam farm needs to know the perimeter to calculate the required length of barbed wire.
Construction of Community Structures: When building small community structures like kiosks, market stalls, or temporary shelters, knowing the dimensions (length and width) and perimeter is essential for estimating materials like wood, zinc, or bamboo.