i ii iii section 2-2 units of measurement ch. 2 - measurement
TRANSCRIPT
I
II
III
Section 2-2
Units of Measurement
CH. 2 - MEASUREMENT
A. Number vs. Quantity Quantity – is something that has magnitude, size,
or amount; number + unit
UNITS MATTER!!
B. SI Units
SI units of measurement is the system that all scientists around the world have agreed upon as the single measurement system.
SI units are defined in terms of standards of measurement.
The standards are objects or natural phenomena that are of constant value, easy to preserve and reproduce, and practical in size.
C. SI Base Units
Quantity Base Unit Abbrev.
Length
Mass
Time
Temp
meter
kilogram
second
kelvin
m
kg
s
K
Amount mole mol
Symbol
l
m
t
T
n
D. SI Prefixes – pg 35
mega- M 106
deci- d 10-1
centi- c 10-2
milli- m 10-3
Prefix Symbol Factor
micro- 10-6
nano- n 10-9
pico- p 10-12
kilo- k 103
BASE UNIT --- 100
E. SI Prefix Conversions A conversion factor is a ratio derived from the equality
between two different units that can be used to convert from one unit to the other.
1. Find the difference between the exponents of the two prefixes.
2. Move the decimal that many places.
To the leftor right?
E. SI Prefix Conversions
mega- M 106
deci- d 10-1
centi- c 10-2
milli- m 10-3
Prefix Symbol Factor
micro- 10-6
nano- n 10-9
pico- p 10-12
kilo- k 103
BASE UNIT --- 100
E. SI Prefix Conversions
Large unit being converted to a smaller unit: Move the decimal place to the right the
specified number of places Small unit being converted to a larger
unit: Move the decimal place to the left the
specified number of places
E. SI Prefix Conversions
mega- M 106
deci- d 10-1
centi- c 10-2
milli- m 10-3
Prefix Symbol Factor
micro- 10-6
nano- n 10-9
pico- p 10-12
kilo- k 103
mo
ve le
ft
mo
ve r
igh
t BASE UNIT --- 100
=
E. SI Prefix Conversions
NUMBERUNIT
NUMBER
UNIT
532 m = _______ km0.532
E. SI Prefix Conversions
1) 2100 g = ______________ kg
2) 5.5 L = ______________ mL
3) 45 km = ______________ m
4) 85 m = ______________ mm
2.1
85,000
45,000
5,500
F. Derived Units
Combination of base units.
Volume (m3 or cm3) – the amount of space occupied by an object length length length
D = MV
1 cm3 = 1 mL1 dm3 = 1 L
Density (kg/m3 or g/cm3) – the ratio of mass to volumemass per volume
G. DensityM
ass
(g)
Volume (cm3)
Δx
Δyslope D
V
M
Density is a characteristic physical property of a substance and does not depend on the size of the sample; the ratio of mass to volume is constant.
G. Density
Density is dependent on temperature.
An increase in temperature usually causes a decrease in density for most substances.
H. Problem-Solving Steps
1. Analyze
2. Plan
3. Compute
4. Evaluate
I. Solving Density Problems
An object has a volume of 825 cm3 and a density of 13.6 g/cm3. Find its mass.
GIVEN:
V = 825 cm3
D = 13.6 g/cm3
M = ?
WORK:
M = DV
M = (13.6 g/cm3)(825cm3)
M = 11,200 g
V
MD
I. Solving Density Problems
A liquid has a density of 0.87 g/mL. What volume is occupied by 25 g of the liquid?
GIVEN:
D = 0.87 g/mL
V = ?
M = 25 g
WORK:
V = M D
V = 25 g
0.87 g/mL
V = 29 mLV
MD
3
3
cm
gcm
J. Dimensional Analysis
The “Factor-Label” Method Units, or “labels” are canceled, or
“factored” out
g
J. Dimensional Analysis
Steps:
1. Identify starting & ending units.
2. Line up conversion factors so units cancel.
3. Multiply all top numbers & divide by each bottom number.
4. Check units & answer.
J. Dimensional Analysis
Your European hairdresser wants to cut your hair 8.0 cm shorter. How many inches will he be cutting off? (Hint: 2.54 cm = 1 inch)
8.0 cm 1 in
2.54 cm= 3.2 in
J. Dimensional Analysis
How many milliliters are in 1.00 quart of milk? (Hint: 1.057 qt = 1 L)
1.00 qt 1 L
1.057 qt = 946 mL
qt mL
1000 mL
1 L