Systems of Units Measurement

The CGS (centimeter, gram, second) system

  • Length is measured in centimeters, mass is measured in grams and time is measured in seconds.
  • Thus centimeter, gram and seconds are the fundamental units of measurement in the CGS system.

MKS (meter, kilogram, second) system 

  • Unit of measurement for length is meter, for mass it is kilogram and for time it is seconds.
  • Thus in this system meter, kilogram and seconds are fundamental units of measurement.
  • This system was used in France and number of other European countries.


FPS (foot, pound, second) system

  • Unit of measurement for length is foot, for mass it is pound and for time it is second.
  • This system is used commonly in Britain and the countries that were under its rule.


SI system

  • In SI system length is measured in meter, mass in kilogram and time in seconds
  • The SI system or the International system of standards has now replaced all the systems of measurement.


Base quantity Name
length meter
mass kilogram
time second
electric current ampere
temperature kelvin
amount of substance mole
luminous intensity candela

Fundamental & Derived Units

Fundamental Units

  • The units of fundamental physical quantities (length, mass & time) are called fundamental units.
  • These units can neither be derived from one another nor can be resolved into any other units.
  • They are independent of one another.


Derived Units

  • Are the units of physical quantities which can be expressed in terms of fundamental units
  • Unit of area can be an example for derived unit. If L is the length of square then L x L = Lis its area. Similarly, the volume of a cube is L x L x L = L3 cubic area.

Fundamental units

Scalar and Vector Quantity

Scalar Quantities 

  • Measurements that strictly refer to the magnitude of the medium – absolutely no directional components
  • Everything from tons to ounces to grams, milliliters, seconds & volume are all scalar quantities, as long as they are applied to the medium being measured and not the movement of the medium.
  • Two more commonly used scalar quantities in physical calculations are speed and temperature. As long as they are not associated with a directional movement, they remain scalar quantities.


Vector Quantities

  • Refers to both the direction of the medium’s movement as well as the measurement of the scalar quantity.
  • Increase/Decrease in Temperature – The measurement of the medium’s temperature is a scalar quantity; the measurement of the increase or decrease in the medium’s temperature is a vector quantity.
  • Velocity – The measurement of the rate at which an object changes position is a vector quantity. For example: If a person quickly moves one step forward and then one step backward there would certainly be a lot of activity; but, there would be “zero velocity.”
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