chapter 2 : section 2. objectives distinguish between a quantity, a unit, and a measurement...
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UNITS OF MEASUREMENTChapter 2 : Section 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
Units of measurement Quantity – magnitude, size, or
amount 5 2,000,000
0.030o Units – compare what is measured
with defined size mL g feet
Quantity has no meaning without the unit 5 mL 100 g 2,000,000
feet
SI Measurement Le Systeme International d’Unites
Adopted 1960 as world-wide agreed upon standards
Base
unit
s
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
Weight – measure of the gravitational pull on matter Example : Moon has 1/6 weight
Visual Concept 1 – Click Here
Visual Concept 2 – Click Here
Metric Prefixes Tera- T 1012 1 000 000 000 000 Giga- G 109 1 000 000 000 Mega- M 106 1 000 000 kilo- k 103 1000 hecto- h 102 100 deka- da 10 10 - - - - deci- d 10-1 0.1 centi- c 10-2 0.01 milli- m 10-3 0.001 micro- u (mu) 10-6 0.000 001 nano- n 10-9 0.000 000 001 pico- p 10-12 0.000 000 000 001
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/moleSpeed : 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.
Write density equation
Step 1:D
V=
m
List your variables
Step 2:D
V
m
=
=
= ?
8.4 g
3.1 cm3
Replace variables in the equation
Step 3:
8.4 g
3.1 cm3
=
Rearrange the equation
Step 4:
SolveStep 5:
2.7 g/cm3=
Rearranging EquationsD
V=
m
Multiply both sides by V
Step 1:
Solve for m:D
V=
m
DV
=m
V Vx x
V’s will cancel out leaving m by itself and on top
Step 2:so: D=m Vx
Solve for V:
Rewrite the equation
Step 3:
Multiply both sides by V
Step 1:
Divide both side by D
Step 2:D
V=
mV Vx x
D = mV xDD
DV =
m
so:
Rewrite the equation
Step 3:
Practice pg.40 #1-31. What is the density of a block of marble that
occupies 310. cm3 and has a mass of 853 g?
2. Diamond has a density of 3.26 g/cm3. What is the mass of a diamond that has a volume of 0.351 cm3?
3. 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?
1.14 g
2.75 g/cm3
5.60 mL
Density of Some Common Substances Substance Density (g/cm3)
Air 0.0013 Feathers 0.0025 Wood(Oak) 0.6 - 0.9 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 = 0.6213 miles
1 dollar 4 quarters4 quarter or 1 dollar
Visual Concept – Click Here
=So: How many quarter are there in $55 ?
55 dollars
x1 dollars
4 quarters = 220
quarters
Making conversions How many miles are in 15 Km?1. Write given value:2. Choose conversion factor3. Multiply top and divide bottom
11.0 miles
x0.6213 miles
1 km = 17.7
km
Video Concept – Click Here
Sample Problem 2.2Express a mass of 5.712 grams in milligrams and in kilograms.
5.172 g
x1 g
1000 mg = 5172
mg
5.172 g x1000 g
1 kg = 0.005172
kg
Practice 1 & 2 pg. 421. Express a length of 16.45 m in
centimeters and in kilometers.
2. Express a mass of 0.014 mg in grams.
1. 1645 cm, 0.01645 km2. 0.000 014 g
Answers: