How Heavy? How Light?

'A feather is light. A stone is heavy. But how do we measure exactly how heavy something is?'

1. What You Will Learn

• Understanding mass — how heavy or light something is
• Units of mass — gram (g) and kilogram (kg)
• Reading a weighing scale
• Estimating and comparing masses
• Adding and subtracting masses
• Using a balance

2. Heavy or Light — What Does It Mean?

Heavy means something has LARGE mass. It is hard to lift. Light means something has SMALL mass. It is easy to lift.

Heavy vs Light

3. Units of Mass

Gram (g)

• A small unit for light items
• A paperclip weighs about 1 g
• A small chocolate weighs about 20 g
• A slice of bread weighs about 25 g

Kilogram (kg)

• A larger unit for heavier items
• A bag of rice weighs 5 kg
• A watermelon weighs about 3 kg
• A brick weighs about 3 kg

Important Conversion

1 kilogram = 1000 grams

4. Using a Weighing Scale

Types of Scales

• Spring Balance: A hook with a spring inside. Heavier objects pull the spring more.
• Digital Scale: Shows the weight as a number on a screen.
• Beam Balance: Two pans that balance when weights are equal.
• Kitchen Scale: Used to weigh food items.

How to Read a Scale

1. Place the item on the pan or hook
2. Wait for the needle or numbers to SETTLE
3. Read the marking at the needle tip
4. Note the unit (g or kg)

5. Estimating Mass

Before weighing, make a SMART guess.

Guessing Tips

• A small apple ≈ 100 g
• A pencil ≈ 10 g
• Your Maths book ≈ 300 g
• A water bottle (full) ≈ 1 kg
• A school bag ≈ 3-5 kg
• Your own weight ≈ 20-35 kg

Activity

Pick up 5 objects. Guess their mass. Then weigh them on a scale. How close were your guesses?

6. Adding and Subtracting Mass

Addition of Mass

Raju buys 2 kg of rice and 1 kg of dal. Total mass = 2 + 1 = 3 kg

Subtraction of Mass

A shopkeeper has 10 kg of sugar. He sells 3 kg 500 g. Leftover = 10 kg - 3 kg 500 g = 6 kg 500 g

Carrying in Addition

Add: 3 kg 750 g + 2 kg 500 g

• 750 g + 500 g = 1250 g = 1 kg 250 g
• 3 kg + 2 kg + 1 kg = 6 kg
• Total = 6 kg 250 g

7. Key Facts

• Mass tells us HOW MUCH MATTER is in an object
• 1 kg = 1000 g
• 500 g = half a kilogram
• 250 g = quarter of a kilogram
• The SAME object weighs the SAME everywhere (on Earth!)
• A BALANCE compares two masses — the heavier side goes down
• We use grams for LIGHT objects and kilograms for HEAVY objects

8. Common Mistakes

'Do NOT confuse MASS and WEIGHT. Mass is the amount of matter. Weight depends on gravity. But for Class 4, we use them similarly.' 'Do NOT forget to convert: 1 kg = 1000 g, not 100 g.' 'Do NOT estimate too quickly — pick up the object to feel its heaviness.' 'Do NOT subtract grams from kilograms directly — convert to the same unit first.' 'Do NOT think a BIG object is ALWAYS heavier. A big balloon is lighter than a small stone.'

9. Fun Activity

Make a Balance

• Take a hanger or a stick
• Tie a string to each end
• Hang small paper cups on each string
• Hang the hanger on a hook
• Put objects in each cup — the heavier side goes DOWN!

Grocery Store Visit Visit a shop with your parents. Look at how things are weighed. Note 5 items with their weights in kg or g.

Weigh Your Lunch Before eating lunch, weigh your lunch box. After eating, weigh the empty box. How much food did you eat?

10. Self-Test

Q1. How many grams make 1 kilogram? Answer: 1000 grams

Q2. A brick weighs 3 kg. What is its mass in grams? Answer: 3 × 1000 = 3000 g

Q3. A bag has 5 kg of potatoes. Another bag has 3 kg 500 g. What is the total mass? Answer: 5 kg + 3 kg 500 g = 8 kg 500 g

Q4. Which is heavier — 1 kg of cotton or 1 kg of iron? Answer: Both are the SAME (1 kg each). The cotton takes more SPACE but the mass is equal.

Q5. A shopkeeper has 20 kg rice. He sells 12 kg 750 g. How much is left? Answer: 20 kg - 12 kg 750 g = 7 kg 250 g

Q6. Convert 5 kg 250 g into grams. Answer: 5 × 1000 + 250 = 5250 g

11. Key Vocabulary