Physics is all dependent on units, definitions, laws, postulates and derivations. Units of quantities are the only constant thing but it is dependent on the system that is used to express the units. The different systems are CGS (centimetre-grams-seconds) system, MKS (metre-kilograms-seconds) system and SI (International System of Units) units.
The reason why units are given such importance is that they give meaning to the numbers that are calculated. Even the value of numbers is dependent on the unit, for example, 3.5 metres and 3500 millimetre where both represent the same physical quantity length.
But using different systems to express the same physical quantities can sometimes be confusing. So SI units were introduced to avoid such misunderstandings and these are universal units for different physical quantities.
Disadvantages of using different units of measurement
Depending upon the area, the system would differ which resulted in a lot of confusion. There were times when people used to measure with the help of their body parts like hands, arms, fingers and legs. For example, in olden days one depa was equal to measure of two arms. The size of arms varies from person to person which made it difficult while purchasing things.
To overcome this in the 13th century Imperial System was introduced in England to measure various quantities like for measurement of length was expressed as a mile, yard, foot and inch and mass was expressed as pounds and ounces.
Advantage of using different units of measurement
Units can be used in the metric system too. The main advantage is the conversion of units ie; there is a change in decimal number placements. For example, 3 feet can be converted to kilometers by shifting the decimal point three places to the left. 1 metre is equal to 0.001 kilometers because 1000 meters is equal to 1 kilometre. Introduction of SI units also helped and made it easy worldwide with the measurements of units like SI unit of electric flux, SI unit of resistivity etc remains the same.
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