Class: Senior Secondary School 1 (SS1, SS 1, SSS1, SSS 1)
Term: 1st Term
Week: 9
Age: 15 years
Duration: 45 minutes
Subject: Wood Work
Curriculum Theme: Vocational Studies
Previous Lesson: Seasoning of Timber and Methods.
Topic: DETERMINATION OF MOISTURE CONTENT IN TIMBER
Subject Matter: Moisture content methods, percentage calculation, laboratory method, moisture measurement.

Specific Objectives

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

Cognitive Domain:

Define moisture content in timber.
State at least two methods for determining moisture content in timber.
Explain the steps involved in the oven-dry method.
Calculate the percentage of moisture content in a given timber sample.

Affective Domain:

Appreciate the importance of determining moisture content in timber for quality work.
Show interest in learning practical methods of timber testing.

Psychomotor Domain:

Identify the equipment used for moisture content determination.
Perform a simple calculation of moisture content using a given formula.

Participate actively in class discussions and activities.
Work collaboratively when required to solve calculation problems.

Reference Materials

The following resources were used in planning this lesson:

9 Years Basic Education Curriculum for Basic Technology.
State Unified Scheme of Work for Wood Work SSS 1.
Akinwande, S. A. (2018). Comprehensive Woodwork for Senior Secondary Schools. Ibadan: University Press PLC.

Instructional Materials

The teacher will teach this lesson with the aid of:

Timber samples (green and seasoned).
Hydrometer (moisture meter).
Weighing scale.
Oven.
Heater.
Calculator.
Whiteboard and markers.

Rationale for the Lesson

This lesson helps pupils understand how to assess the quality of timber, which is important for successful woodworking projects. Knowing the moisture content prevents common defects like warping and cracking, ensuring the durability and stability of finished products.

Prerequisite/Previous Knowledge

Pupils have prior knowledge of different types of timber and their basic properties, as well as the importance of seasoning timber.

Lesson Content/Board Summary

DETERMINATION OF MOISTURE CONTENT IN TIMBER

Definition of Moisture Content in Timber

Moisture content in timber refers to the amount of water present in the wood, expressed as a percentage of the dry weight of the wood. It affects the strength, stability, and workability of timber.

Importance of Determining Moisture Content

The following are reasons why determining moisture content is important:

It helps to prevent defects such as warping, shrinking, and splitting after timber has been used.
It ensures the stability and strength of timber products.
It helps in selecting timber suitable for specific applications.
It is important for proper storage and preservation of timber.
It affects the adhesion of glues and finishes.

Methods of Determining Moisture Content

There are different methods used to determine the moisture content of timber:

Oven-Dry Method (Laboratory Method): This is a precise method where timber samples are weighed, dried in an oven, and then re-weighed. The difference in weight is used to calculate moisture content.
Moisture Meter Method: This method uses an electronic moisture meter that measures the electrical resistance or dielectric properties of the wood, which correlates to its moisture content. It is a quick and non-destructive method.

Steps for Oven-Dry Method (Laboratory Method)

The following are the steps for the oven-dry method:

Select a small, representative sample of timber.
Weigh the sample accurately to get its initial (wet) weight (W1).
Place the sample in a drying oven set at 103 ± 2°C.
Dry the sample until it reaches a constant weight, meaning all moisture has been removed. This usually takes several hours or days.
Weigh the dried sample to get its final (oven-dry) weight (W2).
Calculate the moisture content using the formula.

Calculation of Moisture Content (Percentage)

The moisture content (MC) is calculated using the formula:

MC (%) = [(W1 – W2) / W2] × 100

Where:

W1 = Initial (wet) weight of the timber sample
W2 = Oven-dry weight of the timber sample

Example: A timber sample weighs 250g initially. After oven drying, its weight is 200g. Calculate its moisture content.

MC (%) = [(250g – 200g) / 200g] × 100

MC (%) = [50g / 200g] × 100

MC (%) = 0.25 × 100

MC (%) = 25%

Teaching Methods/Instructional Techniques

Discussion, Lecture, Demonstration, Question and Answer, Visual Aids

Instructional Procedures

Step 1: Introduction

Time: 5 minutes
Teaching Skill: Set Induction
Teacher’s Activity: The teacher greets the pupils and asks them what happens to wood if it is not properly dried before use. The teacher then introduces the topic: “Determination of Moisture Content in Timber.”
Pupils’ Activity: Pupils respond to questions and listen attentively.
Learning Point: Pupils are introduced to the lesson topic and its relevance.

Step 2: Definition and Importance of Moisture Content

Time: 7 minutes
Teaching Skill: Explanation/Clarification
Teacher’s Activity: The teacher defines moisture content in timber and explains its importance using real-life examples of wood defects caused by improper moisture levels. The teacher writes key points on the board.
Pupils’ Activity: Pupils listen, take notes, and ask questions for clarification.
Learning Point: Pupils understand what moisture content is and why its determination is necessary.

Step 3: Methods of Determining Moisture Content

Time: 10 minutes
Teaching Skill: Demonstration/Explanation
Teacher’s Activity: The teacher explains and, if possible, demonstrates the two main methods: the oven-dry method and the moisture meter method. The teacher shows actual or pictorial examples of the equipment used (oven, weighing scale, moisture meter).
Pupils’ Activity: Pupils observe the demonstration, listen to explanations, and identify the equipment.
Learning Point: Pupils learn about the different ways to measure moisture content in timber.

Step 4: Steps for Oven-Dry Method

Time: 7 minutes
Teaching Skill: Instruction/Listing
Teacher’s Activity: The teacher outlines the step-by-step procedure for determining moisture content using the oven-dry method, writing them clearly on the board.
Pupils’ Activity: Pupils listen, copy the steps into their notebooks, and ask questions.
Learning Point: Pupils learn the practical steps involved in the laboratory method of moisture content determination.

Step 5: Calculation of Moisture Content (Percentage)

Time: 8 minutes
Teaching Skill: Problem Solving/Demonstration
Teacher’s Activity: The teacher presents the formula for calculating moisture content and works through an example on the board. The teacher guides pupils to solve a similar problem.
Pupils’ Activity: Pupils copy the formula, follow the example, and attempt to solve the new problem with guidance.
Learning Point: Pupils learn how to apply the formula to calculate moisture content.

Step 6: Class Activity/Practice

Time: 3 minutes
Teaching Skill: Application
Teacher’s Activity: The teacher provides another simple calculation problem for pupils to solve individually or in pairs. For example: “A timber sample initially weighed 300g and after drying, weighed 240g. Calculate its moisture content.”
Pupils’ Activity: Pupils work on the problem and share their answers.
Learning Point: Pupils practice applying the moisture content formula.

Step 7: Evaluation/Review

Time: 5 minutes

Teaching Skill: Questioning/Assessment

Teacher’s Activity: The teacher evaluates the learning by asking the following questions:

Define moisture content in timber.
Mention two methods used for determining moisture content.
State any three reasons why it is important to determine the moisture content of timber.
A timber sample has an initial weight of 400g and an oven-dry weight of 320g. Calculate its moisture content.

Pupils’ Activity: Pupils answer orally and in writing.

Learning Point: Pupils demonstrate understanding of the lesson.

Step 8: Conclusion

Time: 3 minutes
Teaching Skill: Summarization/Assignment
Teacher’s Activity: The teacher summarizes the key points of the lesson, emphasizing the importance of moisture content in woodworking. The teacher gives homework: “Research other factors that affect the quality of timber.”
Pupils’ Activity: Pupils listen to the summary and copy the homework assignment.
Learning Point: Pupils consolidate their learning and prepare for future topics.

Lesson Keywords

Moisture Content – The amount of water present in timber, expressed as a percentage of its dry weight.
Oven-Dry Method – A laboratory method for determining moisture content by drying timber samples in an oven until constant weight.
Moisture Meter – An electronic device used for quickly measuring the moisture content of timber.
Seasoning – The process of reducing the moisture content in timber to an acceptable level.

Differentiation

For pupils who are struggling, the teacher will provide more guided practice with calculations and simplified explanations. For advanced pupils, the teacher will encourage them to research the effects of different moisture content levels on various timber properties and discuss the advantages and disadvantages of each determination method in more detail.

Note for teachers using this lesson plan

Ensure that safety precautions are observed if demonstrating the oven-dry method with actual equipment. If practical demonstration is not possible, use clear diagrams or videos to illustrate the processes. Emphasize the practical application of moisture content knowledge in real-world woodworking scenarios.