1. 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.

2. 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)

3. SI Units SI uses prefixes to denote quantities smaller or larger than the base unit. Ex: centimeter PowerPrefixAbbreviationPowerPrefixAbbreviation 10 -18 atto-a10 1 deka-da 10 -15 femto-f10 2 hecta-h 10 -12 pico-P10 3 kilo-k 10 -9 nano-n10 6 mega-M 10 -6 micro-µ (mu)10 9 giga-G 10 -3 milli-m10 12 tera-T 10 -2 centi-c10 15 peta-P 10 -1 deci-d10 18 exa-E

4. 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.