📏 Chapter 1: Measurements
🔹 Introduction
Physics deals with nature and its laws. It describes these laws both quantitatively and qualitatively. This description involves the measurement of physical quantities like height, weight, time, etc.
For example:
- In a running race, the time taken by runners is measured to decide the winner.
- To determine the mileage of a vehicle, the distance travelled is measured.
🔹 Physical Quantities
The quantities that can be measured are called physical quantities. Examples: mass, length, volume, area, etc.
To measure a quantity, it is compared with a standard known as a unit. Example: The kilogram (kg) is defined as the mass of a certain platinum–iridium block kept at the International Bureau of Weights and Measures. Any body with the same mass is said to have a mass of 1 kg, double mass → 2 kg, and so on.
🔹 Characteristics of a Unit
A unit used to measure a physical quantity should be:
- Well-defined
- Reproducible
- Unchangeable
- Of measurable size
🔹 Classification of Physical Quantities
Fundamental Quantity
A quantity independent of other quantities. Examples: mass, length, time, electric current, temperature, luminous intensity, amount of substance.
Fundamental Unit
The unit of a fundamental quantity. Examples: kilogram (kg), metre (m), second (s), ampere (A), kelvin (K), candela (cd), mole (mol).
Derived Quantity
A quantity dependent on other physical quantities. Examples: area, volume, density, force, velocity.
Derived Unit
The unit of a derived quantity. Examples: m², m³, m/s, kg/m³, N.
🔹 System of Units
A system which defines fundamental units is called a system of units. Common systems:
- FPS system: foot (length), pound (mass), second (time)
- CGS system: centimetre (length), gram (mass), second (time)
- MKS system: metre (length), kilogram (mass), second (time)
- SI system: an extension of MKS with 7 fundamental and 2 supplementary units. It is the internationally
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