Presentation is loading. Please wait.

Presentation is loading. Please wait.

Chapter 2 Measurements and Calculations Or It all adds up!

Similar presentations


Presentation on theme: "Chapter 2 Measurements and Calculations Or It all adds up!"— Presentation transcript:

1 Chapter 2 Measurements and Calculations Or It all adds up!

2 Accuracy and Precision Accuracy is how close your results are to the accepted value. If the accepted value is 12, then 11.99 is accurate.

3 Accuracy and Precision Precision is how close the number are to each other. 7.99, 8.01 and 8.00 are precise. But what if the accepted value is 12?

4 Accuracy and Precision Section 3 Using Scientific Measurements Chapter 2

5 Remember !! Precision Bombing is not necessarily Accurate.

6 Error Error = accepted value – experimental value. Or: What you want – what you got. %Error = (absolute value of error/accepted value)x100 OR [(What you want – what you got) divided by what you want] times 100

7 Accuracy and Precision, continued Sample Problem C A student measures the mass and volume of a substance and calculates its density as 1.40 g/mL. The correct, or accepted, value of the density is 1.30 g/mL. What is the percentage error of the student’s measurement? Section 3 Using Scientific Measurements Chapter 2

8 Accuracy and Precision, continued Error in Measurement Some error or uncertainty always exists in any measurement. skill of the measurer conditions of measurement measuring instruments Section 3 Using Scientific Measurements Chapter 2

9 Accuracy and Precision, continued Sample Problem C Solution Section 3 Using Scientific Measurements Chapter 2

10 Significant Figures Significant figures in a measurement consist of all the digits known with certainty plus one final digit, which is somewhat uncertain or is estimated. The term significant does not mean certain. Section 3 Using Scientific Measurements Chapter 2

11 Reporting Measurements Using Significant Figures Section 3 Using Scientific Measurements Chapter 2

12 Significant Figures Every nonzero reported is a significant figure. Example: 6.938726 How many significant figures? 7 sig figs

13 Significant Figures Zeros between sig figs are significant. Example: 6.1002 How many sig figs? 5

14 Significant Figures Leftmost zeros appearing in front of nonzero digits are not significant. They are placeholders. Example: 0.00035 How many sig figs? 2

15 Significant Figures Zeros at the end of a number and to the right of a decimal place are always significant. (the money rule) 4.00, how many sig figs? 3

16 Significant Figures Zeros at the rightmost end of a measurement that lie to the left of an understood decimal are not significant. They are placeholders. 560,000 sig figs? 2

17 Significant Figures In an exact count, there are an unlimited number of significant figures. Example: 60 minutes in an hour. 2 sig figs

18 Significant Figures, continued Determining the Number of Significant Figures Section 3 Using Scientific Measurements Chapter 2

19 Significant Figures, continued Sample Problem D How many significant figures are in each of the following measurements? a. 28.6 g b. 3440. cm c. 910 m d. 0.046 04 L e. 0.006 700 0 kg Section 3 Using Scientific Measurements Chapter 2

20 Significant Figures, continued Rounding Section 3 Using Scientific Measurements Chapter 2


Download ppt "Chapter 2 Measurements and Calculations Or It all adds up!"

Similar presentations


Ads by Google