Starter  Convert 3 years to weeks then to days then to hours then to minutes then to seconds.

2.2 Units of Measurement

Measurement  Quantitative information  Need a number and a unit (most of time)  Represents a quantity  For example: 2 meters 2 is number 2 is number Meters is unit Meters is unit Length is quantity Length is quantity  Units compare what is being measured to a defined measurement standard

SI Measurement  Le Systeme International d’Unites : SI  System of measurement agreed on all over the world in 1960  Contains 7 base units  units are defined in terms of standards of measurement that are objects or natural occurrence that are of constant value or are easily reproducible  We still use some non-SI units

Important SI Base Units QuantitySymbolUnitAbbreviation Lengthlmeterm Massmkilogramkg Timetseconds TemperatureTKelvinK Amountnmolemol

Prefixes  Prefixes are added to the base unit names to represent quantities smaller or larger Mmega ,000,000larger kkilo ,000larger ccenti /100smaller mmilli /1000smaller μmicro /1,000,000smaller

Mass  Measure of the quantity of matter  SI unit: kg  use g a lot too g  mass vs. weight weight is the measure of gravitational pull on matter weight is the measure of gravitational pull on matter mass does not depend on gravity mass does not depend on gravity on a new planet, mass would be same but weight could change on a new planet, mass would be same but weight could change

Length  SI unit: m  use cm a lot too cm  km is used instead of miles for highway distances and car speeds in most countries km

Derived SI Units  come from combining base units  combine using multiplication or division Example:Area: A = length x width = m x m = m x m = m 2 = m 2

Volume  amount of space occupied by object  SI: m 3 = m x m x m  use cm 3 in lab a lot cm 3cm 3  non-SI: 1 liter = 1000cm 3 = 1000mL

Density  ratio of mass to volume  SI:  characteristic property of substance (doesn’t change with amount ) because as volume increases, mass also increases  density usually decreases as T increases exception: ice is less dense than liquid water so it floats

Example A sample of aluminum metal has a mass of 8.4 g. The volume is 3.1 cm 3. Find the density. KnownUnknown m = 8.4 g D = ? V = 3.1 cm 3

Conversion Factors  ratio that comes from a statement of equality between 2 different units  every conversion factor is equal to 1 Example: statement of equality conversion factor

Conversion Factors  can be multiplied by other numbers without changing the value of the number  since you are just multiplying by 1

Guidelines for Conversions  always consider what unit you are starting and ending with  if you aren’t sure what steps to take, write down all the info you know about the start and end unit to find a connection  always begin with the number and unit you are given with a 1 below it  always cancel units as you go  the larger unit in the conversion factor should usually have a one next to it

Example 1 Convert 5.2 cm to mm cm to mmcm to mm  Known:100 cm = 1 m 1000 mm = 1 m  Must use m as an intermediate

Example 2 Convert kg to mg kg to mgkg to mg  Known:1 kg = 1000 g 1000 mg = 1 g  Must use g as an intermediate

Example 3 Convert 500,000 μg to kg μg to kgμg to kg  Known:1,000,000 μg = 1 g 1 kg = 1000 g  Must use g as an intermediate

Starter 8/12  Convert 3.76 mm to Mm.

Advanced Conversions  One difficult type of conversion deals with squared or cubed units  Be sure to square or cube the conversion factor you are using to cancel all the units  If you tend to forget to square or cube the number in the conversion factor, try rewriting the conversion factor instead of just using the exponent

Example  Convert: 2000 cm 3 to m 3  No intermediate needed OR Known: 100 cm = 1 m cm 3 = cm x cm x cm m 3 = m x m x m

Advanced Conversions  Another difficult type of conversion deals units that are fractions themselves  Be sure convert one unit at a time; don’t try to do both at once  Work on the unit on top first; then work on the unit on the bottom  Setup your work the exact same way

Example  Convert: 350 g/mL to kg/L  No intermediate needed OR Known: 1000 g = 1 kg 1000 mL = 1 L

Combination Example  Convert: 7634 mg/m 3 to Mg/L Known:100 cm = 1 m 1000 mg = 1 g1 cm 3 = 1 mL 1,000,000 g = 1 Mg 1000 mL = 1 L