Class: Senior Secondary School 1 (SS1, SS 1, SSS1, SSS 1)
Term: 3rd Term
Week: 5
Age: 15 years
Duration: 45 minutes
Subject: Physics
Curriculum Theme: Physics
Previous Lesson: Equilibrium of.
Topic: CENTRE OF GRAVITY
Subject Matter: Centre of gravity concept, stability of objects, stable equilibrium, unstable equilibrium, neutral equilibrium, factors affecting stability, determining centre of gravity of uniform solids, determining centre of gravity of non-uniform solids.

Specific Objectives

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

Cognitive Domain:

Define the centre of gravity of an object.
Explain the concept of stability in objects.
Describe the three types of equilibrium: stable, unstable, and neutral.
State the factors that affect the stability of an object.

Affective Domain:

Appreciate the importance of centre of gravity in the design and stability of everyday objects.

Psychomotor Domain:

Perform practical steps to determine the centre of gravity of irregular laminae.
Classify various objects as being in stable, unstable, or neutral equilibrium.

Collaborate effectively during practical activities to determine the centre of gravity.

Reference Materials

The following resources were used in planning this lesson:

9 Years Basic Education Curriculum for Physics (Senior Secondary Education)
State Unified Scheme of Work for Physics
New School Physics by M.W. Anyakoha
Physics for Senior Secondary Schools by P.N. Okeke and P.N. Etuk

Instructional Materials

The teacher will teach this lesson with the aid of:

Cardboard shapes (irregular laminae)
Plumb line
Pin/needle
Stand
Ruler
Different solid objects (e.g., brick, cone, sphere)
Chalkboard

Rationale for the Lesson

This lesson helps pupils understand why some objects are more stable than others and how their weight is distributed. Knowing about the centre of gravity and stability is important for understanding how structures are built and how everyday objects function safely.

Prerequisite/Previous Knowledge

Pupils should have a basic understanding of mass, weight, force, and simple concepts of equilibrium from previous lessons.

Lesson Content/Board Summary

CENTRE OF GRAVITY

Centre of Gravity (C.G.)

The centre of gravity (C.G.) of an object is the imaginary point where the entire weight of the object appears to act, regardless of its orientation. For symmetrical objects with uniform density, the C.G. is at its geometric centre.

Stability of Objects

Stability refers to the ability of an object to return to its original position after being slightly displaced. It is largely determined by the position of its centre of gravity relative to its base of support.

Types of Equilibrium

There are three main types of equilibrium:

Stable Equilibrium: An object is in stable equilibrium if, when slightly displaced, its C.G. is raised, and it returns to its original position. Examples include a brick lying flat on a table or a cone resting on its base.
Unstable Equilibrium: An object is in unstable equilibrium if, when slightly displaced, its C.G. is lowered, and it topples over. Examples include a cone balancing on its apex or a pencil standing on its tip.
Neutral Equilibrium: An object is in neutral equilibrium if, when slightly displaced, its C.G. remains at the same height, and it stays in its new position. Examples include a sphere or a cylinder rolling on a flat surface.

Factors Affecting Stability

The stability of an object is affected by two main factors:

Height of the Centre of Gravity: The lower the centre of gravity, the more stable the object.
Area of the Base of Support: The wider the base of support, the more stable the object.

Determining Centre of Gravity

The centre of gravity can be determined for different types of objects:

For Uniform Solids (e.g., rectangular block, sphere, cylinder): The C.G. is at the geometric centre of the object. For a uniform rod, it is at its midpoint.
For Irregular or Non-Uniform Solids (using plumb line method for laminae):
1. Make at least three small holes near the edge of the lamina.
2. Suspend the lamina freely from one hole using a pin or nail.
3. Hang a plumb line from the same pin and allow it to settle.
4. Draw a vertical line along the plumb line on the lamina.
5. Repeat the process by suspending the lamina from another hole and drawing a second line.
6. The point where the two (or more) lines intersect is the centre of gravity of the lamina.

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, reviews the previous lesson briefly, and then introduces the new topic, “Centre of Gravity,” by asking pupils to consider why some objects are easier to tip over than others.
Pupils’ Activity: Pupils respond to the teacher’s questions and listen attentively to the introduction of the new topic.
Learning Point: Pupils are prepared for the lesson and connect new information to prior knowledge.

Step 2: Explanation of Centre of Gravity

Time: 10 minutes
Teaching Skill: Explanation/Definition
Teacher’s Activity: The teacher defines the centre of gravity (C.G.) and explains its significance as the point where the entire weight of an object acts. The teacher gives examples of C.G. for uniform objects like a cube or a rod.
Pupils’ Activity: Pupils listen, take notes, and ask questions for clarification.
Learning Point: Pupils understand the definition and concept of the centre of gravity.

Step 3: Explanation of Stability and Types of Equilibrium

Time: 10 minutes
Teaching Skill: Elaboration/Illustration
Teacher’s Activity: The teacher explains the concept of stability and describes the three types of equilibrium: stable, unstable, and neutral. The teacher uses various objects (e.g., brick, cone, sphere) to demonstrate and illustrate each type.
Pupils’ Activity: Pupils observe the demonstrations, classify the objects, and describe the characteristics of each type of equilibrium.
Learning Point: Pupils can differentiate between stable, unstable, and neutral equilibrium with practical examples.

Step 4: Factors Affecting Stability

Time: 5 minutes
Teaching Skill: Explanation
Teacher’s Activity: The teacher explains the two main factors affecting stability: the height of the centre of gravity and the area of the base of support. The teacher gives examples, such as why racing cars are built low to the ground.
Pupils’ Activity: Pupils listen, take notes, and relate the factors to real-life situations.
Learning Point: Pupils understand how C.G. height and base area influence stability.

Step 5: Practical Determination of Centre of Gravity

Time: 10 minutes
Teaching Skill: Demonstration/Guidance
Teacher’s Activity: The teacher demonstrates the plumb line method for determining the centre of gravity of an irregular lamina using cardboard shapes, a pin, a stand, and a plumb line. The teacher guides pupils through the steps.
Pupils’ Activity: Pupils observe the demonstration carefully, ask questions, and practice the procedure with provided materials if time permits.
Learning Point: Pupils learn the practical method for finding the centre of gravity of irregular objects.

Step 6: Class Discussion/Application

Time: 5 minutes
Teaching Skill: Question and Answer
Teacher’s Activity: The teacher facilitates a short discussion on real-life applications of centre of gravity and stability, such as in designing vehicles, buildings, or furniture.
Pupils’ Activity: Pupils contribute to the discussion by providing examples and explaining how stability is considered in different designs.
Learning Point: Pupils connect the lesson to practical applications in their daily lives.

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 the centre of gravity of an object.
Mention two factors that affect the stability of an object.
Distinguish between stable and unstable equilibrium, giving one example for each.
Describe the steps involved in determining the centre of gravity of an irregular lamina using the plumb line method.

Pupils’ Activity: Pupils answer orally and in writing.

Learning Point: Pupils demonstrate understanding of the lesson.

Step 8: Conclusion

Time: 2 minutes
Teaching Skill: Summarization
Teacher’s Activity: The teacher summarizes the key points of the lesson on centre of gravity and stability. The teacher then assigns homework, asking pupils to find and draw two objects that exhibit stable equilibrium and two that exhibit unstable equilibrium in their homes.
Pupils’ Activity: Pupils listen to the summary and copy down the homework assignment.
Learning Point: Pupils consolidate their learning and apply it to their environment.

Lesson Keywords

Centre of Gravity (C.G.) – The point where the entire weight of an object appears to act.
Stability – The ability of an object to return to its original position after displacement.
Equilibrium – A state of balance.
Stable Equilibrium – When displaced, the C.G. is raised, and the object returns to its original position.
Unstable Equilibrium – When displaced, the C.G. is lowered, and the object topples over.
Neutral Equilibrium – When displaced, the C.G. remains at the same height, and the object stays in its new position.
Plumb Line – A line with a weight at one end, used to determine a vertical line.

Differentiation

For visual learners, the teacher will use extensive demonstrations with various objects. For pupils who grasp concepts quickly, they will be encouraged to explore more complex examples or design experiments to test stability. Struggling learners will receive additional guidance during practical activities and simplified explanations with more basic examples.

Note for teachers using this lesson plan

Ensure all practical materials are prepared beforehand for smooth demonstrations. Encourage pupils to actively participate in discussions and practical work. Emphasize safety during practical sessions, especially when using pins or sharp objects. Real-life examples should be used to make the concepts relatable and interesting for the pupils.