# S. I. Units - Quantities and Units In science a Quantity is...

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In science a  Quantity  is expressed as the product of a number and a unit. A number without units often has no  meaning to a scientist. A set of standard (agreed upon) units are essential not only in science, but also in  commerce. The most widely accepted system of measurement in the sciences is the  International System otherwise known as S.I. Units. S.I. stands for Le Systéme International. This is also called the  metric system , with which you may already be  familiar. The metric system is easy to learn and use because subdivisions and multiples of base units employ only factors  of 10. Prefices indicate the size of the unit relative to a base unit. Prefix Symbol Multiple of Unit mega- M 1,000,000 or 10 6 kilo- k 1,000 or 10 3 deci- d 0.1 or 10 -1 centi- c 0.01 or 10 -2 milli- m 0.001 or 10 -3 micro- μ 0.000001 or 10 -6 nano- n 10 -9 pico- p 10 -12 The SI system defines seven base quantities, from which all other scientific quantities can be derived. These base  quantities are length, mass, time, electric current, thermodynamic temperature, amount of substance, and  luminous intensity. All other quantities can be derived from these base quantities using the equations of physics  and chemistry. Let's look at the base units for some base and derived quantities. SI Base Quantities

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## This note was uploaded on 10/13/2011 for the course CHEMISTRY 121 taught by Professor Staff during the Fall '10 term at Bangladesh University of Eng and Tech.

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S. I. Units - Quantities and Units In science a Quantity is...

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