Measurements l l l Scientists use two word

  • Slides: 23
Download presentation
Measurements l l l Scientists use two word to describe how good the measurements

Measurements l l l Scientists use two word to describe how good the measurements are Accuracy- how close the measurement is to the actual value Precision- how well can the measurement be repeated

Accuracy vs. Precision Good accuracy Good precision Poor accuracy Poor precision

Accuracy vs. Precision Good accuracy Good precision Poor accuracy Poor precision

Differences l l Accuracy can be true of an individual measurement or the average

Differences l l Accuracy can be true of an individual measurement or the average of several Precision requires several measurements before anything can be said about it

Let’s use a golf anaolgy

Let’s use a golf anaolgy

Accurate? No Precise? Yes 10

Accurate? No Precise? Yes 10

Accurate? Yes Precise? Yes 12

Accurate? Yes Precise? Yes 12

Accurate? No Precise? No 13

Accurate? No Precise? No 13

Accurate? Yes Precise? We cant say! 18

Accurate? Yes Precise? We cant say! 18

Accuracy vs. Precision l Accuracy how close a measurement is to the accepted value

Accuracy vs. Precision l Accuracy how close a measurement is to the accepted value l Precision - how close a series of measurements are to each other ACCURATE = CORRECT PRECISE = CONSISTENT(Reproducible)

In terms of measurement l l l Three students measure the width of the

In terms of measurement l l l Three students measure the width of the classroom to be 10. 2 m, 10. 3 m and 10. 4 m across. Were they precise? Were they accurate?

In Chemistry…. 7. 0 does not equal 7. 00 If your lab partner has

In Chemistry…. 7. 0 does not equal 7. 00 If your lab partner has 5. 50 cm as an answer and you have 5. 5 cm, one of you will not earn credit!!! Because in science 5. 50 cm does not equal 5. 5 cm l How are these measurements different?

Significant Digit Rules l All non-zero digits are significant • 145 has three significant

Significant Digit Rules l All non-zero digits are significant • 145 has three significant digits • 1, 376 has four significant digits Courtesy Christy Johannesson www. nisd. net/communicationsarts/pages/chem

2. Zeros a. Leading Zeros – NEVER significant b. Middle Zeros – ALWAYS significant

2. Zeros a. Leading Zeros – NEVER significant b. Middle Zeros – ALWAYS significant c. Trailing Zeros – SOMETIMES significant (Depends on the presence of a decimal point) i. If decimal point is present: IS significant ii. If decimal point is not present: IS NOT significant

Examples 1. 23. 50 4 sig figs 2. 402 3 sig figs 3. 5,

Examples 1. 23. 50 4 sig figs 2. 402 3 sig figs 3. 5, 280 3 sig figs 4. 0. 080 2 sig figs

Let’s Practice!!! l Take 2 minutes to answer the practice problems at the bottom

Let’s Practice!!! l Take 2 minutes to answer the practice problems at the bottom of the page. l Put your pencil down when you are finished and we can check our answers together.

A Memory Trick – The USA Pacific Atlantic If there is a decimal…. If

A Memory Trick – The USA Pacific Atlantic If there is a decimal…. If there is no decimal…. Start on the left and stop at the first non zero. Start on the right and stop at the first non zero. That # and everything after it is significant!! That # and everything after is are significant! EX: . 03560 g EX: 35600 g

Significant Digits and Calculators Many calculators display several additional, meaningless digits. Be sure to

Significant Digits and Calculators Many calculators display several additional, meaningless digits. Be sure to record your answer with the correct number of significant digits. Calculator answers are not rounded to significant digits. You will have to round-off the answer to the correct number of digits.

Significant Digits l Calculating with Significant Digits • Multiply/Divide - The number of significant

Significant Digits l Calculating with Significant Digits • Multiply/Divide - The number of significant digits in the answer should be equal to the number of significant digits in the least accurate factor. (13. 91 g/cm 3)(23. 3 cm 3) = 324. 103 g 4 SF 324 g

Significant Digits l Calculating with Significant Digits (con’t) • Addition and Subtraction - The

Significant Digits l Calculating with Significant Digits (con’t) • Addition and Subtraction - The number of decimal places in the answer should be equal to the number of decimal places in the number with the fewest decimal places 224 g 3. 75 m. L + 130 g + 4. 1 m. L 7. 85 m. L 7. 9 m. L 354 g 350 g

Significant Digits Practice Problems 5. (15. 30 g) ÷ (6. 4 m. L) 4

Significant Digits Practice Problems 5. (15. 30 g) ÷ (6. 4 m. L) 4 SF 2 SF = 2. 390625 g/m. L 2. 4 g/m. L 6. 18. 9 g - 0. 84 g 18. 1 g 18. 06 g 2 SF

Reporting Measurements l Using significant figures l Report what is known with certainty l

Reporting Measurements l Using significant figures l Report what is known with certainty l Add ONE digit of uncertainty (estimation)

Significant Digits l The purpose of significant digits is to indicate the precision of

Significant Digits l The purpose of significant digits is to indicate the precision of a measurement. l Recording Significant Digits • Significant digits in a measurement include the known digits plus a final estimated digit 1. 19 cm 0 Centimeters 1 2 3 4 5

Practice Measuring 0 cm 1 2 3 4 5 4. 5 cm 0 cm

Practice Measuring 0 cm 1 2 3 4 5 4. 5 cm 0 cm 1 2 3 4 5 4. 54 cm 0 cm 1 2 3 4 5 3. 0 cm

Group 1 word word word word word wordGroup 1 word word word word word word
Measurements in Experiments Measurements in Experiments Scientists performMeasurements in Experiments Measurements in Experiments Scientists perform
Measurements Measurements Learning Objectives EQ Why are scientistsMeasurements Measurements Learning Objectives EQ Why are scientists
WHY DO SCIENTISTS TAKE MEASUREMENTS MEASUREMENTS Every measurementWHY DO SCIENTISTS TAKE MEASUREMENTS MEASUREMENTS Every measurement
WHY DO SCIENTISTS TAKE MEASUREMENTS MEASUREMENTS Every measurementWHY DO SCIENTISTS TAKE MEASUREMENTS MEASUREMENTS Every measurement
Word Meaning Word Meaning Two approaches to wordWord Meaning Word Meaning Two approaches to word
How do Humanists Social Scientists and Scientists UseHow do Humanists Social Scientists and Scientists Use
How do Humanists Social Scientists and Scientists UseHow do Humanists Social Scientists and Scientists Use
How Scientists Work q Scientists use the scientificHow Scientists Work q Scientists use the scientific
Fundamental Techniques and Measurements Mass Measurements Volume MeasurementsFundamental Techniques and Measurements Mass Measurements Volume Measurements
Fundamental Techniques and Measurements Mass Measurements Volume MeasurementsFundamental Techniques and Measurements Mass Measurements Volume Measurements
CHEMISTRY 161 Chapter 3 Measurements Measurements measurements areCHEMISTRY 161 Chapter 3 Measurements Measurements measurements are
MEASUREMENTS Measurements are fundamental to science Measurements mayMEASUREMENTS Measurements are fundamental to science Measurements may
Measurements 1 Background on SI Units Scientists useMeasurements 1 Background on SI Units Scientists use
Making Measurements Two Types of Measurements Qualitative QuantitativeMaking Measurements Two Types of Measurements Qualitative Quantitative
Chapter Two Measurements In Chemistry Measurements in ChemistryChapter Two Measurements In Chemistry Measurements in Chemistry
I MEASUREMENTS A ALL MEASUREMENTS MUST HAVE TWOI MEASUREMENTS A ALL MEASUREMENTS MUST HAVE TWO
MEASUREMENTS Measurement Measurements are uncertain for two reasonsMEASUREMENTS Measurement Measurements are uncertain for two reasons
Scientific Method Scientists use two main approaches toScientific Method Scientists use two main approaches to
Concept 1 3 Scientists use two main formsConcept 1 3 Scientists use two main forms
Scientific Method Scientists use two main forms ofScientific Method Scientists use two main forms of
Scientific Method Scientists use two main forms ofScientific Method Scientists use two main forms of