■ Measurement – Study Notes
1. Importance of Measurement
•Needed to solve real-life problems (e.g., trade, science, technology).
•Ensures accuracy and compatibility in results.
•Provides a standard way to compare values.
2. Physical Quantities
•Definition: Properties of objects/phenomena that can be measured.
•Two types:
•1. Fundamental Quantities → independent, cannot be derived. Examples: Length (m), Mass
(kg), Time (s).
•2. Derived Quantities → formed from fundamental ones. Examples: Area (m²), Volume (m³),
Density (kg/m³).
3. Units and SI System
•Why Units? → Without them, results are inconsistent.
•SI System (1960, Paris): Universally accepted, standardized, all other units derived from them.
•Advantages: Global consistency, easy conversion, scientific acceptance.
4. Units of Measurement
•(a) Length: SI Unit → metre (m). Conversions: 1 m = 100 cm = 1000 mm. Special units: km, AU
(~150 million km), Light Year (~300,000 km/s).
•(b) Mass: SI Unit → kilogram (kg). Conversions: 1 kg = 1000 g, 1 g = 1000 mg, 1 quintal = 100
kg, 1 tonne = 1000 kg.
•(c) Time: SI Unit → second (s). Conversions: 1 min = 60 s, 1 hour = 3600 s.
•(d) Volume: SI Unit → cubic metre (m³). Other units: 1 Litre = 1000 cm³ = 1000 mL.
•(e) Density: Density = Mass / Volume. SI Unit → kg/m³.
5. Derived Units
•Formed from fundamental units.
•Examples: Area = m², Volume = m³, Density = kg/m³.
6. Rules for Writing Units
•Use lowercase for symbols (kg, m³, s).
•No plural form (1000 kg, not 1000 kgs).
•Don’t mix names + symbols (kg/m³ or kilogram per cubic metre).
•No full stops after symbols (60 cm, not 60 cm.).
•Use space or dot for compound units (N·m, not Nm).
7. Least Count
•Definition: Smallest value an instrument can measure.
•Example: A ruler with 1 mm divisions → least count = 1 mm.
