Monday’s Meanderings…

1. Open House tonight – bring a parent & your Buff Binder… drop your lowest grade!!!

2. Calculators - $10 see me quick!

3. Check your grade on the back wall – see me if you were absent for test and binder check Friday. Zeros highlighted can still be fixed. Tutorials: Tu, Th, Fr this week

4. Put page 18 on your handout for today.

5. Get out page 9 to TURN IN!!!

Significant Figures

Nature of Measurement

Part 1 – numberPart 2 - scale (unit) – NO NAKED

NUMBERS!

Examples: 20 grams

6.63 x 10-34 Joule seconds

Measurement - quantitative observation consisting of 2 parts

Significant Figures

All of the known digits + 1 estimated digit

7.21 cm

Uncertainty of Measurement

The last digit on any physical measurement is always an approximation.

Significant figures are the number of digits that can be accurately measured and the first uncertain digit.

Rule #1

All non-zero numbers are significant (numbers 1-9)

3.89 = __significant figures

938.3 = ___ significant figures

3

4

Rule #2Sandwich rule: all zero’s between non-zero or significant numbers are significant

202 = __ significant figures3

Rule #2

67000045 = __ significant figures

1.50098 = __ significant figures

8

6

Rule #3

Leading zeros are NOT significant (zeros at the front of a 1-9 number)

Rule #3 Leading zeros are NEVER significant

0.91 = ___significant figures

0.0089 = __significant figures

2

2

Rule #4

Trailing (after) zeros are only significant if there is a decimal place in the number

202.00 = __significant figures

5

1000. = ___ sig figs

45000 = ___ sig figs

450.000 = ___ sig figs

0.004500500 = ___ sig figs

4

2

6

7

Practice the zero rules:

10.0098 = __sig digs

9800 = __ sig digs

0.009800 = ___sig digs

6

4

2

Rule #5Numbers obtained through counting or are defined have unlimited significant figures

60 minutes = 1 hour 24 people

Significant Figures in Calculations

An answer cannot be more precise than the least precise measurement in the calculation

PLACE VALUE AND ROUNDING NUMBERS

6354.2178

thousands

hundreds

tens

ones

tenths

thousandths

hundreths

Ten-thousandths

ROUND THIS NUMBER: 9429.9385

1) nearest hundredth

2) nearest ones

3) nearest tens

4) nearest hundreds

5) nearest thousands

RoundingLook at the digit to the right of the one you need to round. If is is < 5 – leave it alone If it is 5 – round up

56.312 m = _____ (4 sig figs) 56.31 m

Rounding

0.001775 m = ___________ (2 sig figs) 0.0018 m

8792 m = _____________ (2 sig figs) 8800 m

To Do!Open up to page 17

On back in top margin do this:Round these numbers to 3 sig figs:1) 346782) 0.0008399673) 120080

Multiplication and Division

The answer should be rounded to the same number of significant figures as the least number of significant figures in the problem

Examples

4.56m x 1.4m = 5cm x 11cm = 0.0001800in x 19.35in =

6.4 m2

60 cm2

0.003483 in2

Addition and Subtraction

Answers should be rounded to the same place value as the least number of decimal places in the calculation

Examples

12.52 m + 349.0 m = 361.52 m = 361.5 m

74.626 m – 28.34 m = 46.286 m = 46.29 m

Examples

34 cm + 45.0 cm = 79 cm

46.7 mL + 52.34 mL = 99.04 mL = 99.0 mL

HUMP DAY!!! 9/17On the bottom of pg. 17 (back) write a 3-5 sentence summary about sig figs. Make sure to answer the ESQ.

Add your “A” to your star with Sharpie.

Come get your calculator!

Edit page 18 WITHOUT CHEATING!!!

Trade & Grade!!!

Accuracy and Precision p. 19

9/17Obj: collect data and make measurements with accuracy and precision. ESQ: How is lab equipment used to measure precisely?

Accuracy

Measurement of how close a measurement comes to the actual or true value

Precision

Reproducibility of data Need more than one measurement

Accuracy and Precision

Accurate and Precise

xxx

Accuracy and Precision

Not Accurate but they are precise

x

xx

Accuracy and Precision

Accurate but Not Precise

xxx

Accuracy and Precision

Not Accurate and Not Precise

xx

x

Data Sets

The data set is accurate if the values are close to the true value (literature value)

Data Sets

The data set is precise if all of the values are close to each other.

Accurate or Precise?

Several groups of students were testing different balances. They tested each balance several times using a 5.01 g weight.

Accurate or Precise?

Balance

Trial#1

Trial#2

Trial#3

Accurate?

Precise?

A 4.98 5.01 5.00

B 4.05 3.98 4.00

Mass (g)

Yes Yes

No Yes

Accurate or Precise?

Balance

Trial#1

Trial#2

Trial#3

Accurate?

Precise?

C 3.57 6.04 4.59

D 5.09 4.92 4.99

Mass (g)

NoNo

Yes No

Precision of Lab Equipment

Precision refers to the reproducibility of data The more precise a piece of equipment, the more likely you are to get the same measurement repeatedly.

Precision of Lab Equipment

The more precise piece of equipment has the smallest increment change between the markings

Precision of Lab Equipment

20

30

Increment = 1 mL

20

22

21

Increment = 0.2 mL

20.2020.00

21.020.0

More Precise

a)

or

More graduations – your measurements will be more precise

b)

or

More graduations – your measurements will be more precise

c)

or

More graduations – your measurements will be more precise

d)

or

More graduations – your measurements will be more precise

Measuring Precisely:

markings = 1 mLprecision = 0.1 mL

36.4 mL

Measuring Precisely:

Markings = 0.1 cmPrecision = 0.01 cm

11.65 cm

On the back of p. 19Color Name of

equipmentMarking increments

Precision Measurement

Red

Orange

Yellow

Green

Blue

Purple