Lecture Notes: Units and Dimensions

Introduction to Physical Units

• Units are used to express the value and similarities of quantities.
• Units give quantities a dimension and a face value.
• Physical quantity is measured based on a standard unit accepted by society.
• Every measurement consists of:
  • A number (e.g. 30)
  • A unit (e.g. meters)

Systems of Units

• CGS: Centimeter, Gram, Second system
• FPS: Foot, Pound, Second system
• MKS: Meter, Kilogram, Second system
• MKSA: Meter, Kilogram, Second, Ampere unit
• British System: Inches and Pounds
• SI Unit: International System of Units, widely used in science and engineering

Basic SI Units and Quantities

• Mass: Kilogram (kg)
• Length: Meter (m)
• Time: Second (s)
• Electric Current: Ampere (A)
• Temperature: Kelvin (K)
• Luminous Intensity: Candela (cd)
• Amount of Substance: Mole (mol)

Supplementary Units

• Radian: For measuring angles
• Steradian: For measuring solid angles

Rules for Writing Units

• Do not write units in plural forms.
• Avoid punctuations within or at the end of units.
• Write units fully or use agreed symbols.

Derived Units

• Formed by combining two or more base units.
• Examples:
  • Area: Meter squared (m²) - Combination of meters
  • Volume: Meter cubed (m³) - Combination of meters
  • Velocity: Meters per second (m/s)
  • Acceleration: Meters per second squared (m/s²)
  • Angular Velocity: Radians per second (rad/s)
  • Density: Kilogram per cubic meter (kg/m³)
  • Pressure: Newton per square meter (N/m²)

Class Activity

• Students are encouraged to list two derived quantities in the comment box.