Measurements — Class 6 Science (Samacheer Kalvi)
TN State Board (Samacheer Kalvi) Class 6 Science, Term 1 — Chapter 1. Measuring length, mass and time.
1. About this chapter
This chapter covers physical quantities, the SI system, the units and instruments for length, mass and time, unit conversions, and measuring irregular volumes.
2. Physical quantities and the SI system
- A physical quantity is anything that can be measured. Every measurement has two parts — a number and a unit.
- SI stands for the International System of Units (Système International). The SI units are: length → metre (m), mass → kilogram (kg), time → second (s).
3. Measuring length, mass and time
- Length is the distance between one end and the other end; its unit is the metre. Lengths in order: km > m > cm > mm.
- The girth (round measure) of a tree is measured with a measuring tape.
- Mass is measured with a beam balance; the SI unit is the kilogram.
- Time is measured with a clock/watch; the SI unit is the second (s).
4. Unit conversions and irregular volume
- Length conversions: 1 m = 100 cm, 1 km = 1000 m. So 7 m = 700 cm and 5 km = 5000 m.
- The volume of an irregular object is found by the displacement of water method (the rise in water level gives the volume).
5. Worked examples
Example 1. Convert 7 m into cm. 7 × 100 = 700 cm.
Example 2. Name the instrument for measuring mass. A beam balance.
Example 3. How do you find the volume of an irregular stone? By the displacement of water method.
6. Book-back questions (Samacheer Kalvi)
I. Choose the correct answer
- The girth of a tree is measured using a — (a) ruler / (b) measuring tape. Ans: (b) measuring tape.
- 7 m converted into cm is — (a) 70 cm / (b) 700 cm. Ans: (b) 700 cm.
- The correct order of lengths is — (a) km > m > cm > mm / (b) mm > cm > m > km. Ans: (a) km > m > cm > mm.
- Five kilometres is equal to — (a) 5000 m / (b) 500 m. Ans: (a) 5000 m.
- The volume of an irregular object is found by the — (a) ruler method / (b) displacement of water method. Ans: (b) displacement of water.
II. Fill in the blanks / one word 6. The full form of SI is the International System of Units. 7. An instrument used for measuring mass is the beam balance. 8. The SI unit of mass is the kilogram. 9. The two parts present in a measurement are a number and a unit. 10. Time is measured in seconds.
III. Odd one out 11. Kilogram, millimetre, centimetre, nanometre — the odd one is kilogram (it measures mass; the others measure length).
7. Common mistakes
- Mistake: Writing a measurement without a unit. Fix: Every measurement needs a number and a unit.
- Mistake: Confusing the SI unit of mass with weight. Fix: The SI unit of mass is the kilogram.
- Mistake: Using a ruler for irregular volumes. Fix: Use the displacement of water method.
8. Quick revision
- Term 1 · Ch 1 · measurements.
- Physical quantity = measurable; measurement = number + unit; SI = International System of Units.
- Length → metre (km > m > cm > mm), mass → kilogram (beam balance), time → second.
- 1 m = 100 cm, 1 km = 1000 m; irregular volume by displacement of water.
