SI Units• SI units are the Système Internationale units created in 1960

and used by nearly all countries in the world as a standard. SI has seven base units:• meter for length• kilogram for mass (note: not the gram)• second for time• Ampere for electric current• Kelvin for temperature• Candela for luminous intensity• mole for the amount of substance

SI units are written in lowercase.

SI Units

• The base units measure dimensions. (Remember dimensions are physical quantities, a unit is a

measurement of a dimension)

Derived units are formed by combining the seven base units by multiplying or dividing.(ex: speed = distance/time)

SI Units

• SI uses prefixes to denote quantities smaller or larger than the base unit. Ex: centimeter

Power Prefix Abbreviation Power Prefix Abbreviation

10-18 atto- a 101 deka- da

10-15 femto- f 102 hecta- h

10-12 pico- P 103 kilo- k

10-9 nano- n 106 mega- M

10-6 micro- µ (mu) 109 giga- G

10-3 milli- m 1012 tera- T

10-2 centi- c 1015 peta- P

10-1 deci- d 1018 exa- E

SI Units• To convert measurements between prefixes, use

dimensional analysis (a form of ratios) with the quantity you want in the numerator.

Ex1: Write 2.56 m as mm.Ex2: Write 4.5 mm as km.Ex3: Write 0.567 m as nm.Ex4: A human hair is approximately 50 µm in diameter. Express this in meters.