Physical Quantities and Units | Physics for Grade 12 PDF Download

What is a Physical Quantity?

• Speed and velocity are examples of physical quantities; both can be measured
• All physical quantities consist of a numerical magnitude and a unit
• In physics, every letter of the alphabet (and most of the Greek alphabet) is used to represent these physical quantities
• These letters, without any context, are meaningless
• To represent a physical quantity, it must contain both a numerical value and the unit in which it was measured
• The letter v be used to represent the physical quantities of velocity, volume or voltage
• The units provide the context as to what v refers to
  • If v represents velocity, the unit would be m s^–1
  • If v represents volume, the unit would be m³
  • If v represents voltage, the unit would be V

All physical quantities must have a numerical magnitude and a unit

Estimating Physical Quantities

• There are important physical quantities to learn in physics
• It is useful to know these physical quantities, they are particularly useful when making estimates
• A few examples of useful quantities to memorise are given in the table below (this is by no means an exhaustive list)

Estimating Physical Quantities Table

Worked Example 
Estimate the energy required for an adult man to walk up a flight of stairs.