Download Ch 2.3 How to take measurements and make proper calculations

Ch 5 How to take measurements and
make proper calculations
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We will deal with many types of
measurements and calculations
throughout the year. The types of
values you will encounter are given
data, collected data, and calculated
data. Knowing what and how to
handle these numbers is essential.
Taking Measurements
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When taking measurements it is important that
you are as accurate and precise as possible.
Accuracy is how close your measurement is to the
correct value.
Precision is how closely your measurements are
to each other.
Being precise also involves taking your
measurements to the maximum number of digits.
Using the right equipment will help in both
precision and accuracy.
Use of Significant Figures
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The precision of a collected value or calculated
value is indicated by the number of significant
figures the number contains.
The greater the number of significant figures the
greater the precision.
Making calculations with numbers should not
change their significance.
Use the rules of significant figures to correctly
round off your calculator values.
Exact Numbers
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Exact numbers have infinite precision.
Only collected measurements are under
the rules of significant figures.
Numbers that are indicating exact amounts
are not included.
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A dozen people
45 atoms
Divided among 6 groups
Significant figure rules
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Non-zero digits are significant
Zeros between non-zero digits are
significant
Zeros at the end of a number are not
significant unless the are after the decimal
point.
Zeros at the beginning of a number less
than 1 are not significant.
How many Significant Figures?
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1.021
253
500
0.00203
6.022
.0004
22.34
Using Significant Figures
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Rule for multiplication/division
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Round the answer to the number indicated by
the calculated value with the least number of
significant figures
Rule for addition/subtraction
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Round the answer to the place of the least
significant number by place
Using Significant Figures
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Rule #1 Multiplication/Division
The mass of an object is 5.0 grams and its
volume is 2.75 mL. Calculate its density.
D = m/V D = 5.0/2.75 = 1.81818181818
Round this off to 1.8 because of the 5.0
value has 2 sig. figs.
Using Significant Figures
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Rule #2 Addition/Subtraction
212.2 + 26.7 + 402.09 =
641.0
Raw is 640.99, round to the least significant
place