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# As Physics watch

1. What is the purpose of SI units?
2. (Original post by hhaq170)
what is the purpose of si units?
s-i ( international system of units)

combines metric system and (mks) (cgs) systems to create a single composite system of units

Physics is all about physical quantities in other words quantities that can be measured or determined numerically

there are many types:
1.scalars
2.vectors
3.base quantities
4. Derived quantities
etc...(these should be more than enough for a-levels)

you probably know scalars and vectors

base quantities are expressed in terms of base units
1.metre
2.kilogram
3.second
4.ampere
5.kelvin
6.candela
7.mol

and dervied quantities (such as speed , current, acceleration etc..)

are expressed as combinations of base units
example
speed=distance/time=metre/sec>> this contains two base units so its a derived physical quantity

get the idea?? Rep if you get it!
3. Thanks a lot. I get it now.

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Updated: September 16, 2015
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