[Physics Form 4] Quantities Defined

A physical quantity represents any property that can be measured by a scientific device and technique, and given a numerical value.



Classification of quantities



Physical quantities

1. Base quantities
   
   
   • Base quantities cannot be expressed in terms of other physical quantities while derived quantities are combination of two or more base quantities.
   • The five base quantities are current, length, mass, temperature and time.
     
     
     
     
2. Derived quantities
   
   
   • Derived quantities result from the combination of base quantities through multiplication and divisive operations only.
   • Mathematical operations like subtraction and addition are not involved.
     
     Eg: Work is a derived quantity because it is obtained through the combination of three base quantities - mass, length and time.
     
     
     
     Work = Force x Displacement
     
     Work = Mass x Acceleration x Displacement
     
     Work = (Mass x Velocity x Displacement) / Time
     
     Work = [Mass x (Displacement)²] / (Time)²
     
     
     
     Note: Displacement is measured in terms of length.
     
     
     
     
3. Scalar quantities
   
   
   • Scalar quantities describe only the magnitude of physical quantities.
     
     
     
     
4. Vector quantities
   
   
   • Vector quantities describe both the magnitude and direction of physical quantities.