1. Chapter 2 : Section 2
UNITS OF MEASUREMENT

2. 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

3. 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

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

5. 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

6. 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

7. 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

8. 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

9. Rearranging Equationsm 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

10. 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

11. 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 

12. 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

13. 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

14. 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

15. 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