Transcript Chapter 2 Standards of Measurement

Chapter 2
Standards of Measurement
Objectives:
Understand Mass and Weight (2.1)
Identify the metric units of measurement (2.6)
Explain what causes uncertainty in measurements
(2.7, 2.8 – 2.12)
Learn how to use significant digits and scientific
notation (2.2 – 2.5)
Dimensional Analysis (2.8)
Density (2.12)
The Metric System (2.6)
The International System of Units
Standards of measurement
Base units (7) – see Table 2.2 (pg 20)
1.
2.
3.
4.
5.
6.
7.
MASS:
LENGTH:
TIME:
COUNT, QUANTITY:
TEMPERATURE:
ELECTRIC CURRENT:
LUMINOUS INSTENSITY:
The Metric System
Derived Units:









AREA:
VOLUME:
ENERGY:
FORCE:
PRESSURE:
POWER:
VOLTAGE:
FREQUENCY:
ELECTRIC CHARGE:
The Metric System
Metric Prefixes – make base unit larger
or smaller
Table 2.1 – must know bolded prefixes
Based on 10
Math method vs. “Stairs”
Conversion Practice
Convert a volume of 12 microliters into
centiliters
Express a distance of 15 meters in
kilometers
Which is the longer amount of time, 1351
ps or 1.2 ns?
Uncertainty in Measurement
Why are digits in measurements uncertain?
1. Instruments never completely free of flaws
2. Always involves estimation
 Choose the right instrument for the job
 May be estimated for you (electronic
scales)
 Scale is marked but you estimate the inbetween
Uncertainty in Measurement
Precision:
Accuracy:
Significant Digits
All digits known with certainty plus one
final digit which is uncertain (or estimated)
All non-zeros are significant (143.34)
A zero is significant when :
– It is between nonzero digits (2004)
–
A zero is not significant when:
–
–
Significant Digits - PRACTICE
How many significant digits?
1. 54.23
2. 23.00005
3. 0.0004
4. 35000
5. 0.000504
6. 45.623200
7. 5,000,000
8. 4,000,000.1
Significant Digits - Calculations
Addition and Subtraction
– Round answer to have final digit in the SAME
PLACE as the last digit in the LEAST
ACCURATE MEASUREMENT
1.21 + 5.002 + 10. =
34.5 + 12.45 + 23.0505 =
186.31 + 11.1 =
12.0231 + 3.86 =
0.100012 + 120. =
1200 + 12 + 15 + 0.5 =
Significant Digits - Calculations
Multiplication and Division
– The answer has as many sig figs as the
number with the
14.8 x 3.1 =
18.2 x 3.0 =
52/1.5 =
321.868783 x 1 =
2400 x 2.123 =
15000/12.354 =
Scientific Notation
Convenient way of writing very large or
very small numbers and showing only
significant figures
Number between
5120 becomes
Move decimal point in original number to
make number
Move left = ; move right =
Scientific Notation Practice
123,000 =
0.000045 =
23.45 =
0.0000000003 =
1,000,000 =
Scientific Notation
Adding and subtracting
– Numbers must be the SAME POWER
– 1.4 x 104 + 2.1 x 105 (must change to
21.0 x 104) and then =
– 3.2 x 103 + 1.8 x 102 =
Scientific Notation
Multiplying
–
– (2.0 x 103) x (3.0 x 104) =
Dividing
–
– (8.2 x 108) / (4.1 x 104) =
Types of Measurements
Mass – amount of matter in a body
–
Weight – measure of earth’s gravitational
attraction for that object
–
–
Types of Measurements
Volume – the amount of space occupied
by matter
–
–
Temperature – measure of the intensity of
heat (figure 2.6)
–
–
–
Conversion Factors
Enable movement between metric system
and “English” system
See back cover of book and Appendix III
Common conversions you should
memorize
Dimensional Analysis
(Problem Solving)
Remember:
A technique of converting between units
Dimensional Analysis
(Problem Solving)
Conversion Factors: ratio derived from the
equality between 2 different units
CF can be written either way
Dimensional Analysis
(Problem Solving)
The “t” method
Conversion
Factor
Dimensional Analysis
(Problem Solving)
How many seconds are in 4.15 hours?
If a student needs 1.5 mL of water, how many
cups does he need?
Density
Common ratio used in
chemistry
Physical property of a
substance
Mass/volume
D= m
v
SI units: kg/m3
Solid
– g/cm3
Liquid
– g/mL
Gas
– g/L
Can change
due to
temperature
and/or
pressure
changes
Density
1. Find the density of a piece of metal with a
volume of 2.7 cm3 and a mass of 10.8 g.
2. Determine the mass of an object with a density
of 0.24 g/cm3 and a volume of 2 cm3.
!!!