1. Units, Measurement, Significant Figures & Conversions Physics

2. SI Units The SI Units we will be concerned with mostly are: QuantityUnit Length/Distance Time Mass Temperature meter [m] second [s] kilogram [kg] Kelvin [K]

3. SI Units All of our other units will be based on meters, kilograms, seconds, and Kelvins. This is referred to as the mks unit system Other systems: cgs; ft/lb/s

4. Making Measurements All measurements must contain both 1. A number 2. A unit Measured values are reported such that only the last digit is uncertain. ALL digits of a measurement, including the last one, are called significant figures. Aka: Sig figs

5. Measuring Length Length measurements are made in units of meters.

6. Length Measurements 1011121314  What is the measurement? A) 12.92 m B) 12 m C) 12.9 m

7. Length Measurements 1011121314  What is the measurement? A) 10.3 m B) 10.28 m C) 10 m

8. Length Measurements 1011121314  What is the measurement? A) 11.5 m B) 11.55 m C) 11 m

9. Sig Fig Rules All nonzero digits are significant. Ex: 2.54 has ____ sig figs Ex: 167.965 has ____ sig figs Zero Rules A zero is significant when it appears between two nonzero digits Ex: 2.04 has ____ sig figs Ex: 10.065 has ____ sig figs 3 6 3 5

10. Sig Fig Rules Zero Rules cont. A zero is significant when it appears at the end of a number AND to the right of the decimal Ex: 4.900 has ____ sig figs Ex: 17.0 has ____ sig figs 4 3

11. Sig Fig Rules Zero Rules cont. A zero is NEVER significant when it appears in front of a number Ex: 0.007865 has ____ sig figs Ex: 0.09 has ____ sig fig 4 1

12. Sig Fig Rules Zero Rules cont. A zero is SOMETIMES significant when it appears at the end of a number AND to the left of the decimal For this course, assume these zeros ARE NOT significant unless you read “precisely” or “exactly” in front of the number Ex: 20 has ____ sig fig Ex: 3400 has ____ sig figs 1 2

13. Sig Fig Rules A good rule-of-thumb for the zeros in sig figs is this: Convert the number to scientific notation and if the zeros drop out then they are not significant Ex: 0.007865 = 7.865 x 10 -3 So it has 4 sig figs Ex: 3400 = 3.4 x 10 2 So it has 2 sig figs

14. Try it! How many sig figs are in each of the following? 1. 0.000743 A) 3B) 6C) 7

15. Try it! How many sig figs are in each of the following? 1. 0.000743 2. 10.47 A) 2B) 3C) 4

16. Try it! How many sig figs are in each of the following? 1. 0.000743 2. 10.47 3. 219,976.900 A) 5B) 9C) 11

17. Try it! How many sig figs are in each of the following? 1. 0.000743 2. 10.47 3. 219,976.900 4. 4.00000009 A) 2B) 8C) 9

18. Try it! How many sig figs are in each of the following? 1. 0.000743 2. 10.47 3. 219,976.900 4. 4.00000009 5. 0.0072 A) 2B) 4C) 5

19. Accuracy & Precision Two types of numbers in scientific work: 1. Exact numbers 2. Inexact numbers Measurements are inexact due to equipment and human error. Precision & accuracy are used to describe the uncertainty of measured values.

20. Accuracy & Precision Precision refers to how reproducible individual measurements are Accuracy refers to how closely individual measurements agree with the “true” or accepted value

21. Accuracy & Precision Precise but not accurate Accurate but not precise

22. Accuracy & Precision Neither accurate nor precise Both accurate and precise GOOD BAD

23. Unit Conversions Notes on board

24. Try It! 183 cm equals how many meters? First, choose a conversion factor: A)B)C) Then do the calculation: A) 1.83 m B) 18.3 mC) 18300 m 1 m 100 cm 10 mm 1 cm 1,000 m 1 km

25. Try It! 8,700 milligrams is how many grams? First, choose a conversion factor: A)B)C) Then do the calculation: A) 0.87g B) 87.0 gC) 8.7 g 1000 mg 1 g 1000 kg 1 g 1000 mg

26. Try It! 4.3 Astronomical Units (A.U.) is equal to how many kilometers? First, choose a conversion factor: A)B)C) Then do the calculation: A) 6.4 km B) 6.432 x 10 8 km C) 6.4 x 10 8 km 1 A.U. 149,597,870.7 km 1 A.U. 149,597.8707 m 1 A.U.