Measurement

Grade 8 · General Science

Semester 1 | Period 1 | Week 2

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Subject: General Science

Semester: 1

Period: 1

Week: 2

School Name:
Teacher’s Name:
Subject: General Science
Grade Level: Grade 8
Date: Week 2
Lesson Duration: 45 minutes
Week & Period: Week 2, Period 1
Topic: Measurement
Sub-topic: Meaning and Importance of Measurement, Basic and Derived Units

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

  1. Define measurement and explain its importance in science.
  2. Identify basic units of measurement for length, mass, time, temperature, and electric current.
  3. Describe derived units such as area, volume, density, weight, and force and demonstrate simple calculations.

Previous Knowledge
Students already know:
• Observations and use of simple measuring tools in daily life.
• Basic numeracy skills for calculation.

Instructional Materials
• Textbook: General science textbooks for Grade 8
• Teaching aids: Rulers, metre rules, weighing scales, stopwatches, measuring cylinders, thermometers, calculators
• Students' notebooks and writing materials

Lesson Development – ABC Model

A – Anticipation (Warm-up / Starter)
Time: 5–10 minutes
Activity: The teacher will ask the class:
• How do you measure the length of a table or the weight of a bag of rice?
• Why is it important to have a standard way of measuring things?
The teacher will record responses on the board.

Teacher’s Role: Guide discussion on the need for measurement in daily life and science.
Learner’s Role:
• Share examples of measurement in daily activities.
• Respond verbally and actively participate.

B – Building Knowledge (Main Lesson Body)

Time: 25–30 minutes

  1. Meaning and Importance of Measurement in Science

Teacher’s Role:

  • Explain that measurement is the process of finding the size, length, weight, or quantity of something using agreed standards (SI units).
  • Stress that science depends on accuracy (being exact), standardization (same unit everywhere), and repeatability (others can repeat the experiment and get the same result).
  • Give reasons why measurement is important:
    • Without accurate measurement, experiments cannot be trusted.
    • Standardization ensures everyone around the world understands results (e.g., 1 kilogram in Liberia is the same as in America).
    • Measurement makes comparison possible (e.g., comparing rainfall in Monrovia vs. Gbarnga).

Liberian Examples:

  • Traders in Red Light Market measure rice in kilograms for fair selling.
  • Doctors measure patients’ body temperature with a thermometer for diagnosis.
  • Engineers measure land in square metres before building houses.

Learners’ Activities:

  • Discuss what might happen if people used different “local measures” (e.g., one person’s “cup” of rice vs. another person’s).
  • Brainstorm daily activities in their communities where measurement is necessary.

Assessment Check:

  1. Define measurement in your own words.
  2. Why is measurement important in science and in daily life?

 

  1. Basic Units (SI Units)

Teacher’s Role:

  • Introduce the internationally accepted SI (Système International) units used in science.
  • Write on the board and explain:
    • Length → metre (m)
    • Mass → kilogram (kg)
    • Time → second (s)
    • Temperature → Kelvin (K) / Celsius (°C)
    • Electric current → Ampere (A)
  • Explain instruments used:
    • Ruler/tape (for length), balance (for mass), stopwatch (for time), thermometer (for temperature), ammeter (for current).

Learners’ Activities:

  • Use rulers to measure the length of their exercise books.
  • Use a balance to weigh an object (chalk box, small stone).
  • Time how long it takes for one student to walk across the classroom using a stopwatch.

Assessment Check:

  1. State the SI unit of length, mass, and time.
  2. Which instrument is used to measure temperature?

 

  1. Derived Units

Teacher’s Role:

  • Explain that derived units are obtained by combining two or more basic units.
  • Write and explain the following examples:
    • Area = length × width → measured in square metres (m²)
    • Volume = length × width × height → measured in cubic metres (m³) or litres (L)
    • Density = mass ÷ volume → measured in kg/m³
    • Weight = mass × acceleration due to gravity (9.8 m/s²) → measured in Newtons (N)
    • Force = mass × acceleration → measured in Newtons (N)

Worked Examples:

  1. If a classroom is 8 m long and 5 m wide, area = 8 × 5 = 40 m².
  2. If a box has length 2 m, width 1 m, and height 0.5 m, volume = 2 × 1 × 0.5 = 1 m³.
  3. An object of mass 200 g (0.2 kg) displaces 50 cm³ (0.00005 m³) of water. Density = 0.2 ÷ 0.00005 = 4000 kg/m³.
  4. A boy of mass 50 kg has weight = 50 × 9.8 = 490 N.

Learners’ Activities:

  • Measure the length and width of the classroom and calculate the area.
  • Use a measuring cylinder to find the volume of water in different containers.
  • Calculate density: Measure the mass of a stone with a balance, then place it in water to find displaced volume, then calculate.
  • Discuss Liberian examples:
    • Farmers measuring farmland in square metres.
    • Villagers measuring the volume of water stored in wells.
    • Cocoa beans weighed in kilograms before export.

Assessment Check:

  1. What is the SI unit of area?
  2. If a box has length 3 m, width 2 m, and height 0.5 m, calculate its volume.
  3. A block of mass 10 kg has a volume of 0.005 m³. Calculate its density.
  4. A man has a mass of 70 kg. What is his weight on earth?

 

  1. Conversions Between Units

Teacher’s Role:

  • Teach common conversions in measurement.
    • 1 km = 1000 m
    • 1 cm = 0.01 m
    • 1 litre = 1 dm³ = 1000 cm³
    • 1 km² = 1,000,000 m²
  • Emphasize the importance of conversions in experiments and real-life applications.

Learners’ Activities:

  • Convert 250 cm into metres.
  • Convert 2.5 km into metres.
  • Convert 2000 mL of water into litres.

Assessment Check:

  1. Convert 1500 m into km.
  2. Convert 3.5 L into cm³.
  3. How many metres are in 0.25 km?

 

  1. Summary Notes (for learners to copy)
  • Measurement ensures accuracy, fairness, and standardization in science and daily life.
  • Basic Units (SI Units): metre (m), kilogram (kg), second (s), Kelvin (K)/Celsius (°C), Ampere (A).
  • Derived Units: area (m²), volume (m³ or L), density (kg/m³), weight (N), force (N).
  • Conversions: 1 km = 1000 m; 1 L = 1000 cm³; 1 km² = 1,000,000 m².
  • Examples in Liberia: weighing rice and cocoa, measuring rainfall in litres, measuring farmland in square metres.

C – Consolidation (Conclusion & Assessment)
Time: 5–10 minutes
Summary: Teacher asks students to recall:
• Definition of measurement and its importance.
• Examples of basic and derived units.
• How measurements are applied in daily life and science.

Evaluation Method (Expanded):
• Exit slip/quiz: Students will write short answers to:

  1. Define measurement.
  2. Give two examples of derived units.
    Teacher collects and provides oral feedback.

Assignment (Expanded):
• Measure the perimeter and area of a rectangular object at home or school.
• Calculate the density of a small object using mass and volume.
• Research local Liberian examples where measurement is used in trade, agriculture, or construction.

Differentiation / Inclusive Strategies
• Struggling Learners: Guide with step-by-step measurement activities and use of visual aids.
• Advanced Learners: Solve multi-step problems involving conversions and derived unit calculations.
• Students with Disabilities: Provide adapted tools and one-on-one support.

Teacher’s Reflection (After Class)
• What worked well? ______________________________________________________
• What needs improvement? _________________________________________________
• Students’ engagement level: □ High □ Medium □ Low