Physics, Measurements and Particles, 1-4

  • 1 Measurements and Units
    • 1.2 Standard Form

Measurements and Units

Standard Form

Scientific Notation/Standard Form

SI Units

\label{SI Units}SI Units
Base Quantity Name Symbol
Length Metre m
Mass Kilogram kg
Time Second s
Electric Current Ampere A
Thermodynamic Temperature Kelvin K
Amount of Substance Mole mol
Luminous Intensity Candela cd

All derived units can be defined in terms of SI base units. The kilogram is the only base unit not based on a universal constant.


Experimental error can be random or systematic.

  • Random errors can be environmental or in reading errors

  • Systematic errors lead to consistently incorrect results

    • Instrumental error

    • Poor experimental design

Accuracy, Precision, and Uncertainty

  • A measurement is repeatable if the experiment gives consistent results

  • A measurement is reproducible if it is repeatable using different techniques in different labs

  • A measurement is accurate if it is close to the true value

  • A measurement is precise if it gives a small range of answers

  • The resolution of a measurement device is the smallest increment it can measure

Combining Uncertainties

  • When adding or subtracting quantities, you should add their absolute uncertainties

  • When multiplying quantities, you should add their percentage uncertainties


  • Independent variable (cause) on x-axis

  • Dependent variable (effect) on y-axis

  • Uncertainty is \(\pm\) the greatest difference between the best fit and two worst fit lines