Monday, May 03, 2010

[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.

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Nota Terkini