## 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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