Physical Quantities (Cambridge (CIE) A Level Physics)

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

• To represent a physical quantity, it must contain both a numerical value and the unit in which it was measured

• For example, the letter v can be used to represent the physical quantities of velocity, volume or potential difference (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 potential difference, 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