Welcome to Day 8 Aug 26 th , 2009!

1. Welcome to Day 8 Aug 26th, 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. 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) - Accuracy, Precision and % Error

6. 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) Accuracy, Precision and % Error

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

8. 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. Accuracy, Precision and % Error

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

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. Percent Error %E = Vactual – Vmeasured X 100 Vactual |-------| Accuracy, Precision and % Error

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

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

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

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

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

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

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

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

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

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

25. IP

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