Long and Short
"Everything has a length. The question is: how do we MEASURE it?"
1. What You Will Learn
- Units of length: millimetre (mm), centimetre (cm), metre (m), kilometre (km)
- How to ESTIMATE lengths
- How to COMPARE lengths
- How to measure using a RULER
2. Units of Length
| Unit | How Big? | Used For |
|---|---|---|
| Millimetre (mm) | VERY tiny. 10 mm = 1 cm | Thickness of a coin, tip of a pencil |
| Centimetre (cm) | About the width of your finger | Length of a pencil, your hand |
| Metre (m) | About the height of a doorknob | Height of a person, length of a room |
| Kilometre (km) | A long distance | Distance between towns, your school to home |
Important Conversions
- 1 cm = 10 mm
- 1 m = 100 cm
- 1 km = 1,000 m
3. Measuring with a Ruler
A ruler has markings in centimetres (big lines) and millimetres (small lines).
How to Measure:
- Place the '0' mark of the ruler at one end of the object
- Read the number at the other end
- Always measure from ZERO — not from the edge of the ruler
4. Comparing Lengths
Which is LONGER?
- A pencil (15 cm) or an eraser (3 cm)? → The PENCIL
- A school bus (10 m) or a car (4 m)? → The SCHOOL BUS
- The distance from Delhi to Mumbai (1,400 km) or Delhi to Agra (230 km)? → DELHI TO MUMBAI
5. Practice Questions
- Convert: 5 m = ______ cm (Answer: 500 cm)
- Convert: 3 km = ______ m (Answer: 3,000 m)
- A rope is 2 m long. How many cm is that? (Answer: 200 cm)
- The distance from Ravi's house to school is 1.5 km. How many metres? (Answer: 1,500 m)
- Which is longer: 50 cm or 1 m? (Answer: 1 m)
6. Fun Activity
Estimate and Measure:
- Estimate the length of your desk (in cm). Then MEASURE it. How close was your estimate?
- Measure your height (in cm). Compare with your friend. Who is taller? By how many cm?
- How many of your FOOT lengths make 1 metre?
7. Key Vocabulary
| Word | Meaning |
|---|---|
| Length | How long something is |
| Estimate | A good guess |
| Measure | To find the exact size |
| Convert | To change from one unit to another |
