Transcript Tuesday September 15, 2009

Tuesday September 15, 2009
Objectives: SWBAT distinguish between precision and
accuracy.
SWBAT represent numbers in scientific notation.
SWBAT calculate the number of significant figures
SWBAT use dimensional analysis to solve
mathematical problems.
Warm Up 9/15/2009
•
•
•
•
The earth is 2.38 X 10^5 miles from the
moon. How far is that? How far is that in
kilometer if 1 mile = 1.6 km?
How many seconds ARE in one day?
How could I write 4,560,000 in scientific
notation?
What does 3.5X10^-6 mean?
Our Unit Measurements
Mass
Volume
Length
Definition
The measure of
the amount of
matter
The space
occupied by the
object
Measure of a
dimension
Units Used
Kg
L, ml or cm^3
Km, m, cm
Tool Used
Balance
Graduated
cylinder or meter
stick
Meter stick
Method
LWH or
displacement
Volume by Displacement
Meniscus
meniscus
Calculating Volume
Volume = LWH
a) What’s the volume of this box?
b) How many decimal places should we go
to?
Are you accurate or precise?
Accuracy: how close are you to the correct
value?
Precision: How close are you to a value
each time?
Error: experimental value – accepted value
Percent error:
IerrorI
X 100%
accepted value
Calculate %error
How far are you from the intended value?
How close are you?
Example: You record a temperature of
90C° but the correct value for the boiling
point of water is 100C°. What is your
percent error?
Do Decimal Places Matter?
Easy Answer, they are significant!
Measurements must ALWAYS be reported to
the correct number of sig. figs, it’s a matter
of precision.
Which digits are significant?
1. Every non-zero digit.
ex. 24.7m , 0.743m, and 714m
2. Zeroes between nonzero digits.
ex. 7003m , 40.79m, and 1.503m
3. Leftmost zeros are not.
ex. 0.0071m, 0.42m, and 0.000099m
More Rules for Sig Figs
4. Zeros at right of decimal and at end of
number are.
ex. 43.00m, 1.010m, and 9.000m
5. Zeros to the right at the end before the
decimal are not.
ex. 300m, 7000, and 27,210m
6. All digits written in scientific notation are
significant.
Adding/Subtracting Mult/Div
Significant Figures
Addition and Subtraction
Rule: Decimal places should be rounded to same
number of decimal places as the measurement
with the least number of decimal places.
Multiplication and Division
Rule: Round to the answer to the same number of
sig. figs. as the measurement with the least
number of sig. figs.
Last But not Least: Scientific
Notation
Scientific Notation:
There must be a non-zero-digit to the left of
the decimal. The exponent on the tens
should represent the number of “tens”
skipped.
Ex. 6,300,000 = 6.3 X 10^6 (to the left (+))
0.000008 = 8 X 10^-6 (to the right (-))
*digits must be in significant figures!
Homework
R58: #1-5
R61: #1-5
Do this in homework section. Do only a,b for
each.