Physical Quantities

Physical Quantities

In physics, quantities are properties or values that can be measured. Measurement is very important in science as it is usually a means of communication by

scientists and engineers. Hence, the need for a clear understanding of quantities and their units too.

There are two types of quantities and units:

1. Fundamental Quantities/Units: These are the basic quantities in science which do not depend on other quantities neither can they be derived from other quantities. Also, fundamental units are the units of these independent quantities. Examples of fundamental quantities and their units are shown below:

Quantity	Unit
Length	Metre(m)
Mass	Kilogram(kg)
Time	Seconds(s)
Electric current	Ampere(A)
Temperature	Kelvin(K)
Amount of substance	Mole(mol)

 

2. Derived Quantities/Units: These are quantities gotten from the combination of two or more fundamental quantities. Likewise, their units are also gotten from the combination of these fundamental units. Hence, they are dependent quantities/units. The table below shows some derived quantities, their derivations and units:

Derived quantity	Derivation	Derived unit
Area (A)	Length × breadth	m × m = m2
Volume (V)	Length × breadth × height	m × m × m = m3
Density (∫)	Mass/volume	Kg/m3 or kgm-3
Velocity (v)	Displacement/time	m/s or ms-1
Acceleration(a)	Change in velocity/time	m/s/s= m/s2 or ms-2
Force (F)	Mass x acceleration	Newton (N)
Energy or Work (W)	Force x distance	Joule or Nm
Power (P)	Work/time	J/s or Js-1 or Watt (W)
Momentum (ρ)	Mass x velocity	Kgm/s or kgms-1 or Ns
Pressure (P)	Force/Area	N/m2 or Pascal (P)
Frequency (f)	Number of oscillation/time	Hertz
Electric charge	Electric current x time	Coulomb

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