Quantitative Properties and SI Units

Quantitative Measurement and Units

• Quantitative properties (e.g., mass, length, volume) consist of a number followed by a unit, such as $10\,m$.
• Units are defined as arbitrarily decided and universally accepted standards.
• Historical systems include:
  • CGS: centimetre, gram, second.
  • FPS: foot, pound, second.
  • MKS: metre, kilogram, second.

The International System of Units (SI)

• Established in $1960$ by the general conference of weights and measure as a revised metric system.
• The system is based on the decimal system originated in France.
• Seven fundamental SI units:
  • Length ($l$): metre ($m$)
  • Mass ($m$): kilogram ($kg$)
  • Time ($t$): second ($s$)
  • Electric current ($I$): ampere ($A$)
  • Thermodynamic temperature ($T$): Kelvin ($K$)
  • Amount of substance ($n$): mole ($mol$)
  • Luminous intensity: candela ($cd$)

Physical Properties: Mass and Weight

• Mass: An inherent property measuring the quantity of matter; it is constant regardless of position.
• Weight: The result of mass and gravitational attraction; varies with distance from the center of the earth.
• Conversion: $1\,kg = 1000\,g = 10^3\,g$.

Measurements of Length and Volume

• Length: Small chemical dimensions are expressed in fractional SI units:
  • Nanometre ($nm$): $1\,nm = 10^{-9}\,m$.
  • Picometre ($pm$): $1\,pm = 10^{-12}\,m$.
• Volume: The amount of space occupied by a three-dimensional object.
  • SI unit: $(metre)^3$ or $m^3$.
  • Common units: $1\,L = 1\,dm^3 = 1000\,mL = 1000\,cm^3$.
  • Dimension example: $1000\,cm^3 = 10\,cm \times 10\,cm \times 10\,cm$.