📏 Measurement - Grade 3
Understanding Measurement!
Measurement helps us find out how long, heavy, big, or hot something is! We use different units to measure different things.
What We Measure:
• Length - How long or tall something is
• Weight - How heavy something is
• Capacity - How much liquid something holds
• Temperature - How hot or cold something is
📐 Measure Using a Centimetre Ruler
What is a Centimetre?
A centimetre (cm) is a unit of length in the metric system. It's about as wide as your fingernail!
\(1 \text{ centimetre} = 10 \text{ millimetres}\)
Parts of a Centimetre Ruler:
• Numbers - Show centimetres (0, 1, 2, 3...)
• Long lines - Mark each centimetre
• Short lines - Mark each millimetre (10 between cm marks)
• Zero mark - Where you start measuring
Steps to Measure with a Ruler:
- Place the ruler - Line up one end of the object with the ZERO mark
- Keep it straight - Make sure the ruler is flat and straight
- Read the measurement - Look at the other end of the object
- Write the answer - Include the unit (cm)
Example:
A pencil starts at 0 cm and ends at 15 cm on the ruler.
Measurement: The pencil is 15 cm long ✓
💡 Remember: Always start measuring from the ZERO mark, not from the edge of the ruler!
📏 Which Metric Unit of Length is Appropriate?
Metric Units of Length:
| Unit | Symbol | When to Use | Examples |
|---|---|---|---|
| Millimetre | mm | Very small things | Thickness of a coin, ant |
| Centimetre | cm | Small things | Pencil, eraser, book |
| Metre | m | Medium things | Height of person, door, room |
| Kilometre | km | Long distances | Distance between cities, roads |
How to Choose the Right Unit:
- Think about the size - Is it tiny, small, medium, or very long?
- Use millimetres (mm) - For very tiny things you can barely see
- Use centimetres (cm) - For things you can hold in your hand
- Use metres (m) - For things as tall as you or bigger
- Use kilometres (km) - For long trips or distances
🔄 Compare and Convert Metric Units of Length
Metric Conversion Chart:
\(1 \text{ kilometre (km)} = 1000 \text{ metres (m)}\)
\(1 \text{ metre (m)} = 100 \text{ centimetres (cm)}\)
\(1 \text{ centimetre (cm)} = 10 \text{ millimetres (mm)}\)
Converting Units:
Rule 1: Smaller to Larger Units (Divide)
mm → cm: Divide by 10
Example: \(50 \text{ mm} = 50 \div 10 = 5 \text{ cm}\) ✓
cm → m: Divide by 100
Example: \(300 \text{ cm} = 300 \div 100 = 3 \text{ m}\) ✓
m → km: Divide by 1000
Example: \(5000 \text{ m} = 5000 \div 1000 = 5 \text{ km}\) ✓
Rule 2: Larger to Smaller Units (Multiply)
cm → mm: Multiply by 10
Example: \(7 \text{ cm} = 7 \times 10 = 70 \text{ mm}\) ✓
m → cm: Multiply by 100
Example: \(2 \text{ m} = 2 \times 100 = 200 \text{ cm}\) ✓
km → m: Multiply by 1000
Example: \(3 \text{ km} = 3 \times 1000 = 3000 \text{ m}\) ✓
Comparing Lengths:
- Convert to same unit - Change both measurements to the same unit
- Compare the numbers - Which number is bigger?
- Use symbols - Use >, <, or =
Example: Compare 250 cm and 3 m
Convert 3 m to cm: \(3 \times 100 = 300 \text{ cm}\)
Compare: 250 cm < 300 cm
Answer: 250 cm < 3 m ✓
📊 Conversion Tables
Length Conversion Table:
| Kilometres (km) | Metres (m) | Centimetres (cm) | Millimetres (mm) |
|---|---|---|---|
| 1 km | 1000 m | 100,000 cm | 1,000,000 mm |
| — | 1 m | 100 cm | 1000 mm |
| — | — | 1 cm | 10 mm |
Using Conversion Tables:
- Find the starting unit - Look in the left column
- Find the target unit - Look across to that column
- Read the conversion - See how many of the new unit
- Multiply or divide - Convert your number
🔢 Metric Mixed Units
What are Mixed Units?
Mixed units use two different units together to show a measurement more precisely!
Examples:
2 m 45 cm (2 metres and 45 centimetres)
3 km 250 m (3 kilometres and 250 metres)
Converting Mixed Units:
Example 1: Convert to Single Unit
Problem: Convert 3 m 50 cm to centimetres
Step 1: Convert metres to cm: \(3 \text{ m} = 3 \times 100 = 300 \text{ cm}\)
Step 2: Add the cm: \(300 + 50 = 350 \text{ cm}\)
Answer: 3 m 50 cm = 350 cm ✓
Example 2: Convert to Mixed Units
Problem: Convert 475 cm to metres and centimetres
Step 1: Divide by 100: \(475 \div 100 = 4\) remainder \(75\)
Step 2: 4 = metres, 75 = centimetres
Answer: 475 cm = 4 m 75 cm ✓
⚖️ Light and Heavy
What is Weight?
Weight tells us how heavy something is! Light things are easy to lift, heavy things are hard to lift.
Metric Units of Weight:
| Unit | Symbol | When to Use | Examples |
|---|---|---|---|
| Gram | g | Light objects | Letter, apple, pencil |
| Kilogram | kg | Heavy objects | Person, bag of rice, dog |
\(1 \text{ kilogram (kg)} = 1000 \text{ grams (g)}\)
Comparing Light and Heavy:
Light Objects:
• Feather (less than 1 g)
• Pencil (about 5 g)
• Apple (about 200 g)
Heavy Objects:
• Textbook (about 1 kg)
• Watermelon (about 5 kg)
• Child (about 25 kg)
🥤 Holds More or Less
What is Capacity?
Capacity is the amount of liquid a container can hold! It tells us how much water, juice, or milk fits inside.
Metric Units of Capacity:
| Unit | Symbol | When to Use | Examples |
|---|---|---|---|
| Millilitre | ml | Small amounts | Spoon, medicine, cup |
| Litre | L | Large amounts | Bottle, jug, bucket |
\(1 \text{ litre (L)} = 1000 \text{ millilitres (ml)}\)
Comparing Capacity:
Holds Less:
• Teaspoon (5 ml)
• Glass (250 ml)
• Water bottle (500 ml)
Holds More:
• Large bottle (2 L)
• Bucket (10 L)
• Bathtub (100 L)
⚖️🥤 Compare Weight and Capacity
Steps to Compare:
- Check the units - Are they the same?
- Convert if needed - Make both units the same
- Compare the numbers - Which is bigger?
- Use comparison symbols - >, <, or =
Examples:
Weight Comparison:
Compare: 2500 g and 3 kg
Convert: \(3 \text{ kg} = 3 \times 1000 = 3000 \text{ g}\)
Compare: 2500 g < 3000 g
Answer: 2500 g < 3 kg ✓
Capacity Comparison:
Compare: 1500 ml and 1 L
Convert: \(1 \text{ L} = 1 \times 1000 = 1000 \text{ ml}\)
Compare: 1500 ml > 1000 ml
Answer: 1500 ml > 1 L ✓
🌡️ Read a Thermometer
What is a Thermometer?
A thermometer is a tool that measures temperature - how hot or cold something is!
Temperature Units:
Celsius (°C) - Used in most countries including India
Fahrenheit (°F) - Used in some countries like USA
How to Read a Thermometer:
- Look at the scale - Is it Celsius (°C) or Fahrenheit (°F)?
- Find the liquid level - Where does the red/silver line stop?
- Read the number - Look at the number at that level
- Write with unit - Include °C or °F
Common Temperature Reference Points:
| Temperature | What It Means |
|---|---|
| 0°C | Water freezes (ice forms) |
| 25°C | Room temperature (comfortable) |
| 37°C | Normal body temperature |
| 100°C | Water boils (makes steam) |
🌡️ Reasonable Temperature
What is Reasonable Temperature?
A reasonable temperature is one that makes sense for the situation! Hot soup should be hot, ice cream should be cold!
Temperature Ranges:
Cold (Below 15°C):
• Ice cream: -10°C to 0°C
• Refrigerator: 2°C to 4°C
• Cold water: 5°C to 10°C
• Winter day: 10°C to 15°C
Comfortable (15°C to 30°C):
• Pleasant day: 20°C to 25°C
• Room temperature: 22°C to 25°C
• Swimming pool: 26°C to 28°C
• Warm day: 28°C to 30°C
Hot (Above 30°C):
• Hot summer day: 35°C to 40°C
• Very hot day: 40°C to 45°C
• Hot bath water: 40°C to 45°C
• Hot tea/coffee: 60°C to 80°C
• Boiling water: 100°C
Choosing Reasonable Temperatures:
- Think about the activity - What is happening?
- Consider the object - What should it feel like?
- Use common sense - Would this temperature make sense?
- Compare with known temperatures - Is it hotter or colder than room temperature?
Practice Questions:
Q1: Which is a reasonable temperature for ice cream?
a) 50°C b) 25°C c) -5°C
Answer: c) -5°C ✓ (Ice cream is frozen!)
Q2: Which is a reasonable temperature for a sunny day?
a) 5°C b) 28°C c) 80°C
Answer: b) 28°C ✓ (Warm and sunny!)
Q3: Which is a reasonable temperature for hot soup?
a) 10°C b) 70°C c) 150°C
Answer: b) 70°C ✓ (Hot but not boiling!)
📝 Important Formulas Summary
Length Conversions:
\(1 \text{ km} = 1000 \text{ m}\)
\(1 \text{ m} = 100 \text{ cm}\)
\(1 \text{ cm} = 10 \text{ mm}\)
Weight Conversions:
\(1 \text{ kg} = 1000 \text{ g}\)
Capacity Conversions:
\(1 \text{ L} = 1000 \text{ ml}\)
Conversion Rules:
Larger to Smaller: Multiply
Smaller to Larger: Divide
💡 Quick Learning Tips
- ✓ Always start measuring from the zero mark on the ruler
- ✓ Millimetres (mm) for tiny things, centimetres (cm) for small, metres (m) for medium, kilometres (km) for long distances
- ✓ 1 cm = 10 mm, 1 m = 100 cm, 1 km = 1000 m
- ✓ When converting: Multiply when going from large to small units
- ✓ When converting: Divide when going from small to large units
- ✓ Grams (g) for light objects, kilograms (kg) for heavy objects
- ✓ 1 kg = 1000 g
- ✓ Millilitres (ml) for small amounts, litres (L) for large amounts
- ✓ 1 L = 1000 ml
- ✓ Mixed units: 2 m 35 cm means 2 metres AND 35 centimetres
- ✓ When comparing, convert both to the same unit first
- ✓ 0°C = freezing point of water, 100°C = boiling point
- ✓ Room temperature is about 25°C (comfortable)
- ✓ Body temperature is about 37°C (normal)
- ✓ Practice measuring real objects at home!