2 Derived physical quantities

• A derived physical quantity is a quantity that is defined in terms of fundamental quantities (by multiplying or dividing them).
• Examples: volume, speed, acceleration, force, density, pressure.

Worked idea: the volume of a rectangular block is Vol = length × width × height = L₁ × L₂ × L₃. Volume is built from three lengths, so it is derived from length. In the same way:

• area = length × length,
• speed = length ÷ time,
• density = mass ÷ volume = mass ÷ (length)³.