# Chapter 2 : Section 2 UNITS OF MEASUREMENT.

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Chapter 2 : Section 2 UNITS OF MEASUREMENT

Objectives Distinguish between a quantity, a unit, and a measurement standard Name SI units for length, mass, time, volume, and density Distinguish between mass and weight Perform density calculations Transform a statement of equality to a conversion factor

Units of measurement Quantity – magnitude, size, or amount
Units – compare what is measured with defined size mL g feet Quantity has no meaning without the unit 5 mL g ,000,000 feet

SI Measurement Le Systeme International d’Unites Base units
Adopted 1960 as world-wide agreed upon standards Base units

Some SI Base Units Mass – measure of the amount of matter in an object
Grams (g) Electronic scale or triple beam balance Volume – amount of space an object takes up Liters L V = L X W X H (cm3) Graduated cylinder Water displacement Visual Concept 1 – Click Here Visual Concept 2 – Click Here Weight – measure of the gravitational pull on matter Example : Moon has 1/6 weight

Metric Prefixes Tera- T 1012 1 000 000 000 000
Giga- G Mega- M kilo- k hecto- h deka- da deci- d centi- c milli- m micro- u (mu) nano- n pico- p

Derived SI units Combination of SI base units Examples Area m2 L x W
Volume m3 L x W x H Density Kg/m2 mass/volume Molar mass Kg/mol mass/mole Speed : 2 measurements distance divided by time

Volume and Density Volume = Length x Width x Height
1 cm x 1 cm x 1 cm = 1 cm3 Density = mass / Volume Sample Problem 2-1 A sample of aluminum metal has a mass of 8.4 g. The volume of the sample is 3.1 cm3. Calculate the density of aluminum. Step 1: m 8.4 g D = = = 2.7 g/cm3 Step 4: Write density equation V 3.1 cm3 Replace variables in the equation D = ? Step 2: m = 8.4 g Step 5: List your variables Solve V = 3.1 cm3 Step 3: Rearrange the equation

Rearranging Equations
m D = V Solve for m: m V x D = x V Step 1: V Multiply both sides by V Step 3: Step 2: so: m = D x V Rewrite the equation V’s will cancel out leaving m by itself and on top Solve for V: m D = V Step 1: Step 3: m Multiply both sides by V Rewrite the equation V x D = x V V Step 2: V x D = m Divide both side by D D D m V = so: D

Practice pg.40 #1-3 What is the density of a block of marble that occupies 310. cm3 and has a mass of 853 g? Diamond has a density of 3.26 g/cm3. What is the mass of a diamond that has a volume of cm3? What is the volume of a sample of liquid mercury that has a mass of 76.2 g, given that the density of mercury is 13.6 g/mL? 2.75 g/cm3 1.14 g 5.60 mL

Density of Some Common Substances Substance Density (g/cm3)
Air Feathers Wood(Oak) Ice  0.92  Water  1.00 Bricks  1.84 Aluminum  2.70 Steel  7.80 Silver  10.50 Gold  19.30

Conversion Factors Ratio derived from the equality between two different units that can be used to convert from one unit to the other Equalities 1 dollar = 4 quarters 1 kg = 1000 g 1 Km = miles Visual Concept – Click Here 1 dollar 4 quarters 4 quarter or 1 dollar So: How many quarter are there in \$55 ? = 4 quarters 55 dollars x = 220 quarters 1 dollars

Making conversions How many miles are in 15 Km? Write given value:
Video Concept – Click Here Making conversions How many miles are in 15 Km? Write given value: Choose conversion factor Multiply top and divide bottom 1 km 11.0 miles x = 17.7 km miles

Sample Problem 2.2 Express a mass of grams in milligrams and in kilograms. 1000 mg 5.172 g x = 5172 mg 1 g 1 kg 5.172 g x = kg 1000 g

Practice 1 & 2 pg. 42 Express a length of m in centimeters and in kilometers. Express a mass of mg in grams. Answers: cm, km g