Class: Senior Secondary School 1 (SS1, SS 1, SSS1, SSS 1)
Term: 3rd Term
Week: 6
Age: 15 years
Duration: 45 minutes
Subject: Physics
Curriculum Theme: Physics
Previous Lesson: Centre of Gravity.
Topic: EQUILIBRIUM OF BODIES IN LIQUIDS
Subject Matter: Archimedes’ principle, upthrust and buoyancy, law of floatation, density, relative density, hydrometer, verifying Archimedes’ principle, determining density and relative density of common materials

Specific Objectives

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

Cognitive Domain:

State Archimedes’ principle.
Explain why objects float or sink based on density.

Affective Domain:

Observe the effects of buoyancy and upthrust.
Appreciate the applications of Archimedes’ principle in daily life.

Psychomotor Domain:

Verify Archimedes’ principle experimentally.
Measure mass and volume to determine density.
Use a hydrometer to compare liquids.
Determine the density and relative density of common materials.

Collaborate effectively in group activities for practical experiments.

Reference Materials

The following resources were used in planning this lesson:

9 Years Basic Education Curriculum for Physics.
State Unified Scheme of Work for Senior Secondary School Physics.
New School Physics for Senior Secondary Schools.

Instructional Materials

The teacher will teach this lesson with the aid of:

Measuring cylinder
Water container
Spring balance
Objects of different materials (e.g., stone, wood, metal block)
Hydrometer
Weighing balance
Charts illustrating Archimedes’ principle and flotation

Rationale for the Lesson

This lesson helps pupils understand how objects behave when placed in liquids. It explains everyday phenomena like why ships float and why some objects sink, providing a foundation for understanding fluid mechanics and its applications.

Prerequisite/Previous Knowledge

Pupils are assumed to have prior knowledge of mass, volume, force, pressure, and the concept of density from previous lessons.

Lesson Content/Board Summary

Equilibrium of Bodies in Liquids

Archimedes’ Principle

Archimedes’ principle states that when an object is wholly or partially immersed in a fluid, it experiences an upthrust equal to the weight of the fluid displaced.

Mathematically, Upthrust (U) = Weight of fluid displaced (Wf).

Verification of Archimedes’ Principle involves:

Measuring the weight of an object in air using a spring balance.
Measuring the weight of the object when immersed in water.
Calculating the apparent loss in weight (upthrust).
Measuring the weight of the water displaced by the object.
Comparing the upthrust to the weight of the displaced water.

Upthrust and Buoyancy

Upthrust is the upward force exerted by a fluid on an object immersed in it. It acts opposite to the direction of gravity.

Buoyancy is the tendency of an object to float or rise in a fluid due to the upthrust acting on it.

Law of Floatation

The law of floatation states that an object floats in a fluid if the upthrust acting on it is equal to its weight. This also means that for a floating object, the weight of the fluid displaced is equal to the weight of the object.

Conditions for an object to float or sink:

If the density of the object is less than the density of the fluid, the object floats.
If the density of the object is greater than the density of the fluid, the object sinks.
If the density of the object is equal to the density of the fluid, the object remains suspended within the fluid.

Density

Density is defined as mass per unit volume of a substance. It is a measure of how much matter is packed into a given space.

Formula: Density (ρ) = Mass (m) / Volume (V)

The SI unit for density is kilograms per cubic metre (kg/m³) or grams per cubic centimetre (g/cm³).

Relative Density

Relative density (or specific gravity) is the ratio of the density of a substance to the density of a reference substance, usually water at 4°C.

Formula: Relative Density = Density of substance / Density of water

Relative density has no unit because it is a ratio of two similar quantities.

Hydrometer

A hydrometer is an instrument used for measuring the relative density of liquids. It consists of a sealed glass tube with a weighted bottom and a graduated stem.

Principle of operation: It floats higher in denser liquids and lower in less dense liquids, following the principle of floatation.

Uses of hydrometers include:

Checking the charge of car batteries (acidometer).
Measuring the density of milk (lactometer).
Determining the alcohol content in beverages.

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 reviews the previous lesson on pressure in liquids. The teacher then asks pupils what happens when they place a stone and a piece of wood in water to introduce the topic of equilibrium of bodies in liquids.
Pupils’ Activity: Pupils respond to questions and pay attention to the introduction.
Learning Point: Pupils recall previous knowledge and are prepared for the new topic.

Step 2: Archimedes’ Principle and Upthrust

Time: 10 minutes
Teaching Skill: Explanation/Demonstration
Teacher’s Activity: The teacher explains Archimedes’ principle and the concept of upthrust using a spring balance, a measuring cylinder, and an object. The teacher demonstrates how to verify the principle by showing the apparent loss in weight of an immersed object and relating it to the weight of the displaced water.
Pupils’ Activity: Pupils observe the demonstration, take notes, and ask questions for clarification.
Learning Point: Pupils understand Archimedes’ principle and the concept of upthrust.

Step 3: Law of Floatation

Time: 8 minutes
Teaching Skill: Explanation/Illustration
Teacher’s Activity: The teacher explains the law of floatation and the conditions under which objects float, sink, or remain suspended, relating these to the densities of the object and the fluid. The teacher uses examples like a ship floating and a stone sinking.
Pupils’ Activity: Pupils listen, contribute to the discussion with examples, and write down key points.
Learning Point: Pupils understand the conditions for an object to float or sink.

Step 4: Density and Relative Density

Time: 8 minutes
Teaching Skill: Definition/Calculation
Teacher’s Activity: The teacher defines density and relative density, providing their formulas and units. The teacher guides pupils on how to determine the density of an irregular object by measuring its mass and volume (using water displacement).
Pupils’ Activity: Pupils define the terms, copy the formulas, and practice simple calculations.
Learning Point: Pupils can define and calculate density and relative density.

Step 5: Hydrometer

Time: 5 minutes
Teaching Skill: Explanation/Application
Teacher’s Activity: The teacher introduces the hydrometer, explains its principle of operation based on floatation, and discusses its various uses in everyday life (e.g., lactometer, acidometer). The teacher may show a hydrometer if available.
Pupils’ Activity: Pupils observe, listen, and identify the uses of a hydrometer.
Learning Point: Pupils understand what a hydrometer is and its applications.

Step 6: Evaluation/Review

Time: 5 minutes

Teaching Skill: Questioning/Assessment

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

State Archimedes’ principle.
Explain why a wooden block floats on water while a stone of the same size sinks.
Define density and state its SI unit.
Mention two uses of a hydrometer.

Pupils’ Activity: Pupils answer orally and in writing.

Learning Point: Pupils demonstrate understanding of the lesson.

Step 7: Conclusion

Time: 2 minutes
Teaching Skill: Summarization
Teacher’s Activity: The teacher summarizes the key points of the lesson, reiterating Archimedes’ principle, the law of floatation, and the concepts of density, relative density, and the hydrometer. The teacher assigns homework: research practical applications of buoyancy.
Pupils’ Activity: Pupils listen to the summary and note down the homework.
Learning Point: Pupils consolidate their learning and identify areas for further study.

Lesson Keywords

Archimedes’ Principle – States that the upthrust on an immersed object equals the weight of the fluid displaced.
Upthrust – The upward force exerted by a fluid on an immersed object.
Buoyancy – The tendency of an object to float or rise in a fluid.
Law of Floatation – An object floats if its weight is equal to the upthrust acting on it.
Density – Mass per unit volume of a substance.
Relative Density – Ratio of the density of a substance to the density of water.
Hydrometer – An instrument used to measure the relative density of liquids.

Differentiation

For pupils who grasp concepts quickly, the teacher can provide additional problems involving calculations of upthrust and relative density. For pupils needing more support, the teacher can provide simplified diagrams and allow more time for hands-on verification of Archimedes’ principle.

Note for teachers using this lesson plan

Ensure all demonstration materials are ready before the lesson. Encourage pupil participation in discussions and practical activities. Emphasize the real-life applications of the principles taught to make the lesson more engaging and relevant.