2. Accuracy, Precision, Estimation, Measurements!!! 9/14/09

4. Accuracy The degree of closeness of a measured or calculated quantity to its actual (true) value.

5. Precision Also called reproducibility or repeatability, the degree to which further measurements or calculations show the same or similar results.

6. Accuracy and Precision Instruments have a defined PRECISION like  0.02 or  0.05 109.80  0.05

7. Accuracy and Precision Which data set is more precise? Why? TrialMeasurement 1100.01 2 3 99.98 4100.00 Avg100.00 TrialMeasurement 1100.10 2100.00 3 99.88 4100.02 Avg100.00

8. Estimation The calculated approximation of a result which is usable even if input data may be incomplete or uncertain. Common Estimates: –Meter –Centimeter –Millimeter

9. Estimation Use of estimates –Allows you to confirm correct units are being used –Allows you to confirm that you have reached a reasonable answer –Allows you to determine distance or length without taking actual measurements –Allows you to understand/interpret distances or lengths

10. Measurements Main Scientific Units (Si units) –Length – Meters (m) –Volume – Liters (L) –Time – Seconds (s) –Mass – Grams (g) –Force – Newtons (N)

11. Remember your Sig Figs! Significant Figures (Significant Digits) - the digits of a number that carry meaning contributing to its precision Using Sig Figs. How long is this paperclip?

12. Remember your Sig Figs! How long is this paperclip? Are you sure?

13. Remember your Sig Figs! How long is this paperclip? Are you sure?

14. Remember your Sig Figs! How long is this paperclip? Are you sure?

15. Remember your Sig Figs! How long is this paperclip? Are you sure?

16. Remember your Sig Figs Recording Sig Figs –Always write the number of digits you KNOW plus ONE guess –Remember your units!!!

17. Remember your Sig Figs Reading Sig Figs –Remember, the last number is the guess. So the more digits, the more precise the measurement was! –Pacific Atlantic Rule

18. Remember your Sig Figs Using the Pacific-Atlantic Rule! If decimal point is Present start on the Pacific side. If decimal point is Absent, start on the Atlantic Side. Start counting at the first number that isn’t 0 and don’t stop counting! The more significant figures present, the more precise the measurement!

19. Converting Metrics First of all, forget the English system. –1 inch = 2.54 cm –1 mile = 1.61 km –2.2 pounds = 1 kg –33.8 ounces = 1 L –Etc. etc. etc.

20. meter liter gram second kilo hecta deka deci centi milli kmkm cmcm m l dldl mlml kgkg mgmg msms g s m

21. Converting Metrics REMEMBER 10!!! Metric units are based on the powers of ten

22. Converting Metrics

23. Ya Gotta Know... 1000 meters= 1 kilometer 1 meter= 10 decimeters 1 meter= 100 centimeters 1 meter=1000 millimeters

24. Converting You can multiply anything by 1 without changing it Anything divided by itself is 1 I can "cancel" common factors when multiplying fractions

25. Converting 53 centimeters = ??? meters 53 cm X ------------- = m

26. Converting 53 centimeters = ??? meters 53 cm X m ------------- cm = m

27. Converting 53 centimeters = ??? meters 53 cm X 1 m ------------- 100 cm = m

28. Converting 53 centimeters = ??? meters 53 cm X 1 m ------------- 100 cm = 0.53 m

29. Conversion Factor 53 centimeters = ??? meters 53 cm X 1 m ------------- 100 cm = 0.53 m What I want ----------------- What I have X X

30. 27 meters = ??? millimeters 27 m X ------------- = mm What I want ----------------- What I have

31. 27 meters = ??? millimeters 27 m X mm ------------- m = mm What I want ----------------- What I have

32. 27 meters = ??? millimeters 27 m X 1000 mm ------------- 1 m = mm What I want ----------------- What I have

33. 27 meters = ??? millimeters 27 m X 1000 mm ------------- 1 m = 27,000 mm What I want ----------------- What I have X X

34. ??? seconds = 450 milliseconds 450 ms X ------------- = 0.4 50 s What I want ----------------- What I have

35. ??? seconds = 450 milliseconds 450 ms X s ------------- ms = s What I want ----------------- What I have

36. ??? seconds = 450 milliseconds 450 ms X 1 s ------------- 1000 ms = s What I want ----------------- What I have

37. ??? seconds = 450 milliseconds 450 ms X 1 s ------------- 1000 ms = 0.450 s What I want ----------------- What I have

38. 0.087 kilometers = ??? centimeters 0.087 km X cm ------------- km = cm

39. 0.087 kilometers = ??? centimeters 0.087 km X m ------------- km = m = cm cm ------------- m X m

40. 0.087 kilometers = ??? centimeters 0.087 km X = 87 m = 8,700 cm 100 cm ------------- 1 m X 87 m 1000 m ------------- 1 km