**Key Definitions:**
• Unit = standard amount used to measure (metre, cm, handspan)
• Measurement = number + unit (example: 50 cm, 13 handspans)
• SI units = International System of Units used worldwide
**Important Conversions:**
• 1 km = 1000 m
• 1 m = 100 cm
• 1 cm = 10 mm
• 1 inch = 2.54 cm (old unit, rarely used now)
**Steps for Correct Measurement:**
1. Choose correct scale (15 cm for small objects, metre scale for big objects, tape for curved objects)
2. Place scale flat along object length
3. Position eye directly above measurement point
4. Read clearly; if scale broken, read any clear marking and subtract
**Why Standard Units Matter:**
Body parts (handspan, foot) differ person to person → different measurements. Standard metre/cm same everywhere → everyone gets same answer.
**Diagrams to Remember:** Correct scale placement (flat, parallel to object), correct eye position (directly above), broken scale method (read both marks, subtract).
**Don't Confuse:** Centimetre vs millimetre (1 cm = 10 mm, mm is much smaller) | Scale vs measuring tape (scale for straight, tape for curved) | Unit vs number (unit is name like 'm', number is how many like '50').
Q1. Deepa's mother asked the tailor to increase the uniform length by char angula. What does char angula mean?
Answer: A — Char means four and angula means finger width in traditional Indian measurement.
Q2. When Deepa and her friends measured the classroom table using handspans, why did they get different numbers?
Answer: B — Handspan differs from person to person, so each student got a different measurement for the same table.
Q3. What is the SI unit of length?
Answer: C — Metre (m) is the international standard unit of length accepted worldwide.
Q4. How many centimetres are equal to 1 metre?
Answer: B — By definition, 1 metre is divided into 100 equal parts called centimetres.
Q5. Fill in the blank: 1 cm = _____ mm
Answer: B — Each 1 cm section on a scale is further divided into 10 equal parts of 1 mm each.
Q6. If you want to measure the length of your pencil, which scale would be most suitable?
Answer: B — A 15 cm scale is ideal for small objects like pencils; a full metre scale would be too large and inconvenient.
Q7. When measuring the length of a pencil with a scale, where should you position your eye?
Answer: C — Positioning your eye directly above ensures you read the correct measurement without parallax error.
Q8. Your scale's zero marking is broken. To measure a pencil, you align one end at 2 cm and the other at 18 cm. What is the length of the pencil?
Answer: C — When the zero is broken, subtract the smaller reading from the larger: 18 cm − 2 cm = 16 cm.
Q9. Why did different countries decide to use a single International System of Units (SI)?
Answer: C — When people started travelling and trading, having different units in each place created confusion, so one standard system was adopted.
Q10. Which of the following statements is true?
Answer: B — A metre is defined as exactly 100 cm everywhere in the world, unlike body parts which vary in size.
What is a unit of measurement?
A unit is a standard amount used to measure and compare the length or size of objects, like metre, centimetre, or handspan.
Why do different students get different handspan measurements for the same table?
Because each student's handspan is a different size, so using body parts as units gives different numbers.
What is the SI unit of length?
The metre (m) is the SI unit of length, which is the international standard measurement used worldwide.
How many centimetres are in 1 metre?
1 metre = 100 centimetres.
What does 1 mm equal in centimetres?
1 millimetre = 0.1 centimetre (or 1 mm = one-tenth of 1 cm).
What is the correct eye position when measuring length with a scale?
Your eye should be directly above the tip or end of the object you are measuring.
How do you measure length if the zero end of your scale is broken?
Use any clear marking on the scale (like 1.0 cm), measure to the other end, then subtract: final length = larger reading − smaller reading.
Why did ancient Indians use angula (finger width) for measurement?
Angula was a traditional unit used by craftspeople like carpenters and tailors before modern standard units were created.
Which measuring tool is better: a ruler or a tailor's tape?
A ruler is better for straight objects like pencils; a tailor's flexible tape is better for curved things like chest or tree girth.
Why was the International System of Units (SI) created?
When people started travelling between countries, different measurement units caused confusion, so countries agreed on one standard SI system.
What is a unit of measurement? Give one example. [1 mark]
A unit is a standard amount we use to measure things. Examples: metre, centimetre, handspan, foot.
Why did Deepa's friends get different handspan measurements for the same classroom table? Explain in 2-3 sentences. [2 marks]
Think about why handspans differ from person to person, and how this affects measurement results when using body parts as units.
Explain with a daily Indian example why standard units like metre and centimetre are better than body parts like handspan or foot for measuring length. (Hint: Think of a tailor or shopkeeper.) [3 marks]
Compare measurements by different people using body parts vs. using metre scale. A shopkeeper selling 2 metres of cloth gets the same length no matter who measures it with a metre scale, but different lengths if people use their own handspans.
Your metre scale has a broken zero end. Explain the steps you would follow to measure the length of your notebook using this broken scale. Include an example calculation. [5 marks]
Find any clear marking on the scale (like 1 cm or 2 cm), align notebook ends to two clear marks, read both markings, then subtract smaller from larger marking. Example: if notebook aligns from 3 cm to 28 cm, length = 28 − 3 = 25 cm.
True or False: 'A flexible measuring tape and a metre scale are suitable for measuring the same types of objects.' Give one reason for your answer. [2 marks]
A scale is for straight objects (pencil, book), tape is for curved objects (chest, tree girth). They measure different types of things, so the statement is false.
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