1. Welcome to Day 8 Aug 26 th, 2009! SWBAT distinguish between accuracy and precision SWBAT compute percent error SWBAT make correct measurements Catalyst Create a hypothesis, IV, DV, Control group for the following question… -How does a car’s gas mileage change as the tires pressure changes? -- If you have SCIENCE FEE MONEY turn it in -- If you have AGENDA MONEY turn it in

2. Agenda Catalyst (10min) Accuracy, precision (10min) Bulls-eye activity (15min) Measurements (10min) Measurement activity (30min) Percent error ?? Exit Ticket (10min)

3. 5 Bonus Points (next week – 1 pt off everyday) Lab Fee, Safety Contract, Notebook Set-up & Extra Item

4. Accuracy, Precision and Percent Error

5. Accuracy, Precision and % Error Key Point #1: Accuracy is how close you are to the correct or accepted value of a measurement. - (Ex. - throwing a dart close to the bulls eye) -

6. Accuracy, Precision and % Error Key Point #2: Precision is how close a series of measurements are to one another. -REPEATABILITY! (Ex. - throwing a dart and hitting the same spot 3 times in a row)

7. Accuracy, Precision and % Error Accuracy/Precision Worksheet - You will need a ruler and a marker

8. Accuracy, Precision and % Error 1)What was the range (biggest - smallest) of the values for your three trials? 2) How accurate were your drops? Explain. 3) Were your drops precise? Explain.

9. Measurement Notes Key Point #3: Science use International System of Units also known as (SI) WHY?

10. UNITS Volume uses Liters (L) or (mL) Mass uses Grams (g) Length uses Meters (m) Temperature uses Degrees Celsius (  C)

11. Measurement Skills Measuring Mass: (1) Zero Scale (2) Record Mass (3)If non-digital Estimate last digit Measuring Volume: (1) Note increments on graduated cylinder (2) Read bottom of meniscus at eye-level (3) Estimate last digit

12. Measuring Temperature: (1) Note increments on thermometer (2) Estimate last digit

13. Percent error Key Point #3: percent error is a quantitative comparison between your value for a measurement and the true value –Tells you how far off your answer is from the true value.

14. Accuracy, Precision and % Error Percent Error %E = V actual – V measured X 100 V actual |-------|

15. Accuracy, Precision and % Error Percent Error You may never have a negative answer with % error, just drop the negative!

16. Accuracy, Precision and % Error % error: Measuring a string you get 18 cm, but Mr. McKnight tells you the string is actually 20 cm long.

17. Accuracy, Precision and % Error % error: [(20 – 18)/20] x 100

18. Accuracy, Precision and % Error % error: [(20 – 18)/20] x 100 = 10%

19. Accuracy, Precision and % Error % error: Measured: 88 mL Actual: 83 mL

20. Accuracy, Precision and % Error % error: 6.0%

21. Accuracy, Precision and % Error % error: Measured: 140 g Actual: 122 g

22. Accuracy, Precision and % Error % error: 14.8%

23. Accuracy, Precision and % Error % error: Measured: 3438 m Actual: 4888 m

24. Accuracy, Precision and % Error % error: 29.7%

25. IP

26. Write down if it is good or bad accuracy and precision Exit Ticket If you measure the mass of Mr. McKnight to be 222g, but his actual mass is 92g, what is your percent error?