Starter

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

2. 2.2 Units of Measurement

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

4. 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

5. Important SI Base Units

6. Prefixes • Prefixes are added to the base unit names to represent quantities smaller or larger

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

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

9. Derived SI Units • come from combining base units • combine using multiplication or division Example: Area: A = length x width = m x m = m2

10. Volume • amount of space occupied by object • SI: m3 = m x m x m • use cm3 in lab a lot • non-SI: 1 liter = 1000cm3 = 1000mL

11. ratio of mass to volume SI: Density • 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

12. Example A sample of aluminum metal has a mass of 8.4 g. The volume is 3.1 cm3. Find the density.

13. 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

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

15. 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

16. Example 1 Convert 5.2 cm to mm • Known: 100 cm = 1 m 1000 mm = 1 m • Must use m as an intermediate

17. Example 2 Convert 0.020 kg to mg • Known: 1 kg = 1000 g 1000 mg = 1 g • Must use g as an intermediate

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

19. Starter 8/12 • Convert 3.76 mm to Mm.

20. 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

21. Example • Convert: 2000 cm3 to m3 • No intermediate needed Known: 100 cm = 1 m cm3 = cm x cm x cm m3 = m x m x m OR

22. 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

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

24. Combination Example • Convert: 7634 mg/m3 to Mg/L Known: 100 cm = 1 m 1000 mg = 1 g 1 cm3 = 1 mL 1,000,000 g = 1 Mg 1000 mL = 1 L