Transcript Significant Figures

Significant Figures
1. Now, knowing PLORNT, write a
1-3 sentence definition of science.
Homework
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I need those lab safety contracts and
student info sheets, folks!
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Take out those agendas: Worksheet will
be due on Friday.
What IS science?
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Science is vast and complicated, but here’s
one way of summing it up that I think is pretty
darn good.
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Science is both a body of knowledge about the
natural world, and the process by which human
beings develop that knowledge. Natural
explanations of natural phenomena are developed
by rigorously and empirically testing them, and
these explanations are always based upon
reasoned consideration of observable evidence,
are always tentative, and are always constructed
by community consensus.
Significant Figures
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Notebooks out! Title this section of your
notes “Significant Figures.”
This handout can be confusing, we’ll
simplify it.
Significant Figures
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The big ideas:
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Scientists need to know how strong their
measurements are. We use “significant figures” to
show that strength.
The more significant figures a number has, the
stronger the measurement it was.
Using better measurement tools gives you
numbers with more sig figs.
There are rules for figuring out how many sig figs
there are.
Significant Figures
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Say you want to measure this guy from
eartip to eartip.
QuickTime™ and a
decompressor
are needed to see this picture.
Significant Figures
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Say you want to measure this guy from
eartip to eartip.
QuickTime™ and a
decompressor
are needed to see this picture.
Significant Figures
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When you take a measurement, you
can estimate one extra digit beyond the
ones on the instrument, but no more
than one.
The better ruler gave us a more precise
measurement.
Significant Figures
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The Rules! When you figure out sig
figs, always follow these rules in this
order. Let’s practice on this number:
020,670.90
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1. All digits NOT zero are always
significant figures.
Significant Figures
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020,670.90
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2. Final zeroes after a decimal point are
significant.
3. A zero between two significant
numbers is significant.
4. All the zeroes that are left are NOT
significant.
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Sig Figs Practice
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How many sig figs?
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0.00416
Sig Figs Practice
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How many sig figs?
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0.00416
Rule 1: Underline all non-zeroes.
Rule 2: Underline all zeroes trailing at the
end after a decimal point.
Rule 3: Underline all zeroes in between
other underlined numbers.
Rule 4: Cross out anything that’s left.
Sig Figs Practice
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How many sig figs?
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0.00416 =
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5.18 =
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200 =
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200.0 =
Sig Figs Practice
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Come up with 15 significant figures
problems, at least five must include
rounding. You must know the answers
to them.
Write the problems on a fresh sheet of
paper. When you’re done, give your
“sig fig quiz” to another group to solve.
Check their answers when they’re done.
MORE fun with Sig Figs!
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What if somebody measured the area of an
aye-aye ear like this?
QuickTime™ and a
decompressor
are needed to see this picture.
MORE fun with Sig Figs!
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A chain is no stronger than its weakest link.
One bad measurement makes your result
bad.
When you add or subtract, you can never get
more decimal places than the number that
had the LEAST.
When you multiply or divide, you can never
get more sig figs than the WORST of the
numbers that you used.
MORE fun with Sig Figs!
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How many sig figs can each of these
answers have?
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20 x 673 =
0.041 x 248,200 =
3.0800 / 0.003 =
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Rounding Sig Figs
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What if the problem’s answer has too
many sig figs or places past the
decimal? You must round it.
Take 20 x 673. We said that the answer
must have just one sig fig. Here’s how
to get there.
Rounding Sig Figs
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1. Do the operation normally first.
What is 20 x 673?
Rounding Sig Figs
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1. Do the operation normally first.
20 x 673 = 13,460 .
2. Count off the number of sig figs that
you need, starting from the leftmost
significant digit.
Rounding Sig Figs
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1. Do the operation normally first.
20 x 673 = 13,460 .
2. Count off the number of sig figs that
you need, starting from the leftmost
significant digit.
3. The last digit that you count to must
be rounded, the rest that you counted
past will stay the same.
Rounding Sig Figs
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How about adding and subtracting?
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4.87 + 927.3
Rounding Sig Figs
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4.87 + 927.3 = 932.17, but the rule is,
the answer cannot have more numbers
past the decimal place than the original
number that had the least.
Sig Figs Practice
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Try these problems:
30 / 81
90.4 - 0.08
27,483 + 94,780
2.33 x 6.085 x 2.2
Sig Figs Practice
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Like before, design a “quiz” for another
team.
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15 questions.
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Five questions, present a single number and
ask how many sig figs it has.
Ten questions, use multiplication, addition, etc.