The units of fundamental quantities can't be expressed in terms of other units i.e. they do not depend upon other units. Hence, they are basic unit or fundamental units. For example kilogram (kg), second (s), meter (m) etc. The units used to measure the derived quantities involve the combination of two or more than two fundamental units. For example, unit of velocity depends upon the unit of distance and time i.e. the unit of velocity (m/s) can be expressed in terms of two fundamental units m and s. So, it is a derived unit. Thus, derived units are those units which can be expressed in terms of two or more than two fundamental units and are used for measuring derived quantities.
Systems Likewise, the unit of force, newton, involves three fundamental units kg, m and s, the unit of pressure, pascal, also involves kg, m and s. of units. Different people use different systems of units to measure different physical quantities. There are only a few system of units which are more scientific and are accepted as the standard system of units. Following are the most popular system of units for scientific purposes, derived on the basis of units used for measuring fundamental quantities.
FPS system
This system is also known as British system of units. In this system, length, mass and time are measured in foot, pound and second respectively.
CGS System
This is a French system of units. In this system, length, mass and time are measured in centimeter, gram and second respectively.
MKS System
This system is also known as metric system of units. In this system, length, mass and time are measured in meter, kilogram and second respectively.
SI System FPS, CGS and MKS systems involve only three quantities (length, mass and time) as fundamental quantities. These three quantities are insufficient to measure some physical quantities in thermodynamics, current electricity and optics. To solve this problem, in 1960 A.D., the 11th general conference of weight and measure was organized which introduced a logical and rationalized system of units called SI system (System International 'd' units). This system is an extended form of MKS system and involves the several fundamental quantities.
Systems Likewise, the unit of force, newton, involves three fundamental units kg, m and s, the unit of pressure, pascal, also involves kg, m and s. of units. Different people use different systems of units to measure different physical quantities. There are only a few system of units which are more scientific and are accepted as the standard system of units. Following are the most popular system of units for scientific purposes, derived on the basis of units used for measuring fundamental quantities.
FPS system
This system is also known as British system of units. In this system, length, mass and time are measured in foot, pound and second respectively.
CGS System
This is a French system of units. In this system, length, mass and time are measured in centimeter, gram and second respectively.
MKS System
This system is also known as metric system of units. In this system, length, mass and time are measured in meter, kilogram and second respectively.
SI System FPS, CGS and MKS systems involve only three quantities (length, mass and time) as fundamental quantities. These three quantities are insufficient to measure some physical quantities in thermodynamics, current electricity and optics. To solve this problem, in 1960 A.D., the 11th general conference of weight and measure was organized which introduced a logical and rationalized system of units called SI system (System International 'd' units). This system is an extended form of MKS system and involves the several fundamental quantities.
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