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!!!
Monday’s Meanderings…. Open House tonight – bring a parent & your Buff Binder… drop your lowest grade!!! Calculators - $10 see me quick! - PowerPoint PPT Presentation
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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