Significant Figures

1. Now, knowing PLORNT, write a 1-3 sentence definition of science.

Homework I need those lab safety contracts and

student info sheets, folks!

Take out those agendas: Worksheet will be due on Friday.

What IS science? Science is vast and complicated, but here’s one

way of summing it up that I think is pretty darn good. 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 Notebooks out! Title this section of your

notes “Significant Figures.” This handout can be confusing, we’ll

simplify it.

Significant Figures The big ideas:

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 Say you want to measure this guy from

eartip to eartip.

QuickTime™ and a decompressor

are needed to see this picture.

Significant Figures Say you want to measure this guy from

eartip to eartip.

QuickTime™ and a decompressor

are needed to see this picture.

Significant Figures 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 The Rules! When you figure out sig

figs, always follow these rules in this order. Let’s practice on this number: 020,670.90

1. All digits NOT zero are always significant figures.

Significant Figures 020,670.90

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.

Sig Figs Practice How many sig figs?

0.00416

Sig Figs Practice How many sig figs?

0.00416Rule 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 How many sig figs?

0.00416 =

5.18 =

200 =

200.0 =

Sig Figs Practice 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! 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! 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! How many sig figs can each of these

answers have?

20 x 673 = 0.041 x 248,200 = 3.0800 / 0.003 =

Rounding Sig Figs 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 1. Do the operation normally first.

What is 20 x 673?

Rounding Sig Figs 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 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 How about adding and subtracting?

4.87 + 927.3

Rounding Sig Figs 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 Try these problems: 30 / 81 90.4 - 0.08 27,483 + 94,780 2.33 x 6.085 x 2.2

Sig Figs Practice Like before, design a “quiz” for another

team. 15 questions.

Five questions, present a single number and ask how many sig figs it has.

Ten questions, use multiplication, addition, etc.