Measurement, Units and SI

40 lessons, pages 81–120.

  1. Why Scientists Measure — Turning observations into numbers that others can check
  2. Anatomy of a Measurement — Number, unit and uncertainty together
  3. The Need for Standard Units — From cubits and feet to an agreed international system
  4. The International System of Units (SI) — Seven base units and how they fit together
  5. Length: The Metre — Defining the metre and measuring distances
  6. Mass: The Kilogram — The only base unit with a prefix in its name
  7. Time: The Second — Atomic clocks and timing chemical changes
  8. Temperature: The Kelvin — Absolute zero and the thermodynamic scale
  9. Converting Between Celsius and Kelvin — Adding and subtracting 273.15
  10. Amount of Substance: The Mole — Counting particles with the Avogadro constant
  11. Electric Current and Luminous Intensity — The ampere and the candela in brief
  12. Derived Units — Building new units from base units
  13. Area and Volume Units — Square metres, cubic metres, litres and cm³
  14. Density and Its Units — kg m⁻³ and g cm⁻³ as derived units
  15. Named Derived Units — Newton, pascal, joule and watt
  16. SI Prefixes: Scaling Units Up and Down — Powers of ten attached to unit names
  17. Large Prefixes: Kilo, Mega and Giga — Measuring big quantities conveniently
  18. Small Prefixes: Milli, Micro and Nano — Measuring the very small in chemistry
  19. Converting with Prefixes — Moving the decimal point with confidence
  20. Unit Conversions for Area and Volume — Why 1 m³ is 1 000 000 cm³
  21. Scientific Notation — Writing very large and very small numbers
  22. Dimensional Analysis — Conversion factors and cancelling units
  23. Checking Answers with Units — Using units to spot errors in calculations
  24. Measuring Instruments and Their Resolution — Rulers, balances, burettes and thermometers
  25. Reading Scales Correctly — Parallax, meniscus and estimating the last digit
  26. Uncertainty in Measurement — No measurement is perfectly exact
  27. Significant Figures: The Idea — Digits that carry meaning about precision
  28. Rules for Counting Significant Figures — Zeros: leading, captive and trailing
  29. Rounding to Significant Figures — Rounding correctly and avoiding false precision
  30. Significant Figures in Multiplication and Division — The answer follows the least precise value
  31. Decimal Places in Addition and Subtraction — Why the rule differs from multiplication
  32. Exact Numbers and Defined Quantities — Counted values and defined conversion factors
  33. Accuracy and Precision — Closeness to the true value versus closeness together
  34. Random Errors — Scatter in results and how repeats help
  35. Systematic Errors — Zero errors, calibration and consistent bias
  36. Mean, Range and Repeatability — Summarising repeated readings
  37. Percentage Error and Percentage Uncertainty — Comparing results with accepted values
  38. Anomalous Results — Spotting and handling outliers fairly
  39. Measurement in the Chemistry Laboratory — Choosing apparatus for the precision needed
  40. Measurement, Units and SI: Unit Review — Bringing units, prefixes, significant figures and accuracy together