Transcript unit-2-3-accreadings-sig-figs-i-answers

Measured & counted numbers
• When you use a measuring tool to
determine a quantity such as your height or
weight, the numbers you obtain are called
measured numbers.
Counted numbers
Obtained when you count objects
•
2 soccer balls
•
1 watch
•
4 pizzas
Obtained from a defined relationship
•
1 foot = 12 inches
•
1 meters = 100 cm
Not obtained with measuring tools
Measurements:
Accurate or Precise?
Creating definitions and clarifying
terms
Precision
• Precision is the ability to
_______________and come up with the
same value every time.
• It is an indication of __________a series of
measurements are to each other.
• The idea of precision is very closely aligned
with the idea of significant figures.
Precision
• A large number of significant figures
suggests a high degree of precision.
• In our next class we will learn all about sig
figs. Now, relax 
Accuracy
• An indication of how
________________________ (often theoretical)
The closer you are to the real, accepted value, the
more accurate you are.
Accurate or Precise?
Case 1
• In the diagram, what can
we say about the group of
arrows in terms of
accuracy:
precision:
Accurate or Precise?
Case 1
• In the diagram, what can
we say about the group of
arrows in terms of
accuracy:
low (as a group)
precision:
low
Accurate or Precise?
Case 2
• In the diagram, what can
we say about the group of
arrows in terms of
accuracy:
precision:
Accurate or Precise?
Case 2
• In the diagram, what can
we say about the group of
arrows in terms of
accuracy:
low
precision:
high
Accurate or Precise?
Case 3
• In the diagram, what can
we say about the group of
arrows in terms of
accuracy:
precision:
Accurate or Precise?
Case 3
• In the diagram, what can
we say about the group of
arrows in terms of
accuracy:
high
precision:
high
How to read a
measurement scale
Taking measurements
Example b) page 31
Volume readings
Graduated cylinder readings
Experimental uncertainty
• It is the estimated amount by which a
measurement might be in error
• Assume you measured a temperature to be
37.5 C°and the uncertainty was _____
What does this mean?
Experimental uncertainty
This means
Time to practice!
Homework will be collected tomorrow for completion marks
Hebden
page29 #44
page32 #48(A,C,E)
page34 #50(A,D,G)
page35 #51(A,C) and #52(A,B)
I am here to help 
Measurements
• Why do we care??????
• Measured quantities have uncertainties in
them. It is impossible to find the EXACT
value…so what do we use?
Significant figures
• They are measured or meaningful digits.
How do we know if a number is a ‘sig fig’ or
not?
• Let us proceed, shall we?
Two major cases to know
#1: When there are no decimal points
#2: When there are decimal points
#1: when there are no decimal points
• Count every single number you see as a
significant figure, EXCEPT for ZERO.
• BUT…..Zeroes in between two non-zero
digits are significant. All other zeroes are
insignificant.
#1: when there are no decimal points
• How many sig figs do the following
numbers have??
345, 5557, 300, 4120, 4005, 40050
#2: when there are decimal points
• Start from the left side of the number,
ignore all the zero's on the left side of the
decimal points ( aka leading zero's). Only
start counting at the first non zero digit.
Once you start counting, continue until
you run out of digits.
#2: when there are decimal points
• Example: how many sig figs do the
following numbers have?
32.670, 0.0001, 0.034780, 44.4, 00.9090
Significant figures
“sig figs”
0.520
0.0025
500
0.02300
120035
500.
2.0 x 105
3
2
1
4
6
3
2
do not expand
Significant figures
2.5002
0.00650
5001
0.0200300
0.02010
200
200.
2.0 x 102
2. x 102
“sig figs”
5
3
4
6
4
1
3
2
1
Adding and Subtraction with Significant Figures
When adding or subtracting sig figs, only round off the
final answer ( never when still calculating) to the LEAST
NUMBER of decimal places contained in the calculations.
1.
21.036
+ 22.1
Adding and Subtraction with Significant Figures
When adding or subtracting sig figs, only round off the
final answer ( never when still calculating) to the LEAST
NUMBER of decimal places contained in the calculations
3.
301.2256
- 0.36
Adding and Subtraction with Significant Figures
4.
+
8.053 x 104
2.3 x 104
Adding and Subtraction with Significant Figures
5.
2.463 x 105
+ 5.006 x 102
Adding and Subtraction with Significant Figures
6.
5.331 x 10-4
- 2.126 x 10-5
When changing exponents, remember…..if you change the lower
exponent to the higher exponent. You are making the exponent larger
so make the number smaller. It is a trade !
HOMEWORK
• PAGE 40 #57 (A,B,C,E,F,I,J)