Lesson 2: Measurement of Mass

📘 Introduction

Have you ever checked the weight of rice at the market, weighed yourself at home, or read the back of a cereal box? All these involve measuring mass.

Mass is an important part of daily life — we use it in cooking, farming, health, and even buying goods. In this lesson, you’ll master how to measure and convert between different mass units, and solve real-life word problems confidently.

🧠 Key Concepts and Explanations

1. What is Mass?

Mass is the amount of matter in an object — how much “stuff” it contains. It is measured using a balance or scale.

Weight, on the other hand, is the force of gravity acting on mass. In everyday life, we often say “weight” when we mean “mass.”

Important: Mass does not change with location, but weight does!

2. Common Metric Units of Mass

3. When to Use Each Unit

4. Visual Aid

5. Conversion Formulas

🔍 Step-by-Step Sample Problems

Example 1: Convert 12.5 kg to grams.

Example 2: A sack of cocoa weighs 78,000 g. How many kilograms is that?

Example 3: A farmer harvested 3.2 tonnes of yams. Convert to kilograms.

📝 Practice Exercises

A. Fill in the Blanks

1. 0.75 kg = _______ g
2. 4,000 g = _______ kg
3. 2.3 t = _______ kg

B. Match the Object to Its Mass

Match the object to the correct estimate:

• i. A bag of cement — A. 2 g
• ii. A mango — B. 2 kg
• iii. A pin — C. 0.002 kg

C. True or False

1. 1,000 g = 1 tonne
2. 1 kg = 1,000 g
3. A truck weighing 10,000 kg equals 10 tonnes

D. Word Problems

1. Your mother buys 2.25 kg of fish. How many grams is that?
2. A student weighs 38,500 g. What is their weight in kilograms?
3. A truck carries 4 tonnes of beans. How many kg is that?
4. If a 12-kg sack of rice is shared equally among 4 friends, how much does each receive?

✅ Answers and Explanations

• 0.75 kg = 750 g
• 4,000 g = 4 kg
• 2.3 t = 2,300 kg
• i → B (2 kg), ii → A (2 g), iii → C (0.002 kg)
• 1. False, 2. True, 3. True
• 2.25 × 1000 = 2250 g
• 38,500 ÷ 1000 = 38.5 kg
• 4 t = 4 × 1000 = 4000 kg
• 12 kg ÷ 4 = 3 kg per person

🔁 Recap

Mass is a measurement of how much matter is in an object. The most used units are g, kg, and tonnes. You can convert between them by multiplying or dividing by 1,000. Always check your units and label your answers correctly.

🪞 Reflection Prompt

Think of 3 items at home you could weigh — one in grams, one in kilograms, and one in tonnes (estimated). Why is it important to use the correct unit for each?