Topic 1 · 1.1–1.2 · Free
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Chapter 1 — Chapter 1 — Measurements
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📘Easy summary
All measurable quantities used to describe physical phenomena are called physical quantities. A physical quantity has a numerical magnitude and a unit. Base quantities (length, mass, time, electric current, temperature, amount of substance, luminous intensity) are defined independently; their SI base units are metre, kilogram, second, ampere, kelvin, mole and candela. Derived quantities (area, velocity, force, energy) are expressed in terms of base quantities, and their units (m², m s⁻¹, newton, joule) are derived units. Very large or small numbers are written in scientific notation (one non-zero digit before the decimal point × power of ten) and with prefixes such as kilo (10³), mega (10⁶), milli (10⁻³), micro (10⁻⁶) and nano (10⁻⁹).
⭐Key points
- 7 base quantities and SI base units.
- Derived units from base units, e.g. N = kg m s⁻².
- Scientific notation and prefixes.
🔬Diagram
🌿Real-life example
Force: 1 N = 1 kg m s⁻²; 0.00052 m = 5.2 × 10⁻⁴ m = 0.52 mm.
💡Exam tip
- Write units in symbols with correct powers (m s⁻¹, not m/s/s).
✅Quick check
1. The SI unit of amount of substance is:
2. Prefix micro means:
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