Physics Tools and Standards

1. Physics Tools and Standards Each discipline has a language. The language of physics is math! What are the mathematical tools you need to succeed?

2. Measurements • We need a way to standardize measurements • Compare to a known quantity • Must be constant, repeatable, and agreed upon by all users

3. Measurements • Constant, repeatable, agreed upon • Divide into groups of 3 • What is the size of the lab tables? • What is the time it takes for a pencil to fall from the 2nd story to the ground?

4. Measurements • Was your data reproducible? How could you test this? • How did you agree upon the standard? • Did you use estimates if your measurement was not an exact number of your standard? How did you estimate? • How accurate were you? How could you be more accurate?

5. Metric System and SI Units • Standard measurements based on powers of 10 • SI units standardized and accepted by scientists worldwide • All your answers will include the SI unit!

6. Derived units are combinations of the base units. Ex: speed is measured in meters per second or m/s

7. SI Prefixes

9. How To: Converting Units • Remember factor-label method? • Multiply your quantity in one unit by a conversion factor that =1 to convert to another unit • REMEMBER- units are your friend! Keep them involved and you will succeed.

10. How to: Converting Units Ex: convert 10 m to cm 1. Draw a big T 2. Put your starting number in the top left and its same unit in the bottom right

11. How to: Converting Units 3. Write the unit that you want in the top right 4. Add numbers to your conversion factor to make it =1. (how many cm in a m or vice versa)

12. How to: Converting Units 5. Multiply through and cross out units that cancel out. *** You can do these conversions in multiple steps***

13. Practice Problems p. 7 #5-8

14. UNITS ARE YOUR FRIEND!!! Treat units as algebraic quantities in your calculations and keep them superglued to their numbers! When you do this and the units of your answer are correct, then your answer should be as well.

16. Scientific Notation • Really big or really small numbers can be a bummer to write and work with • You can get either really big numbers by using positive powers like 1 x 105 = 100 000 • You can also show really small numbers by using negative powers like 1 x 10-5 = 0.00001 • Don’t worry about using your calculator to figure out what these mean- just move the decimal point left (negative exponent) or right (positive exponent) the number of spaces given by the exponent

17. The Power of Powers • Powers of 10 used in scientific notation mean big differences in th evalue of a number • For example: • 106 sec is about 12 days • 109 sec is about 32 years • 1012 sec is about 32000 years!

18. How to Read Scientific Notation Now try 2 x 10-9

19. How to Write Scientific Notation • Move decimal so only 1 nonzero # is to the left of the decimal • Count how many spaces you moved the decimal- if you moved right the exponent is negative and if you moved left it is positive • Get rid of any nonsignificant digits (more on this later) • Write the number multiplied by 10 to the power of however many spaces you moved in step 2

20. Practice Problems 1. Write the following numbers in scientific notation. 1.156 21.8 0.0068 27.635 0.219 444 2. Write out the following numbers in full with the correct number of zeroes. 8.69x104 9.1x103 8.8x10-1

21. Scientific Notation and Calculators • On your calculator, scientific notation is often shown using the letter “E” • So 9.2 x 10-4 would be written 9.2 E -4 • To enter a number look for the EE or Exp key

22. Try it on your calculator • To check yourself, multiply 6.0 x 105 times 4.0 x 103 on your calculator. Your answer should be 2.4 x 109.

23. Accuracy and Precision No measurement is perfectly exact!

24. Precision • Degree of exactness • Written as +n ex: 40.1+1mm • Increase precision by finer divisions of the scale • This meter stick has divisions down to the mm so you can be precise to 0.5mm

25. Accuracy • Are your measurements correct? • Calibration checks measuring tools against a standard

26. Significant Digits • Valid digits in a measurement • Depends on the scale used • Using top ruler, we are certain of 2.5 and are guessing 2.55 so 2 sig digs • Using the bottom ruler we are certain of 2 and are guessing 2.5 so 1 sig dig

27. Sig Digs • What if your measurement falls exactly on the line of 2.5mm? • Record it as 2.50mm because you are certain to within 0.01mm

28. Sig Digs: the rules • Nonzero digits always sig • Final zeros after a decimal pt always sig • Zeros btwn other sigs are always sig • Final zeros that are not after a decimal pt are unknown- • 3400 could have 2,3,or 4 sig digs • Write it in scientific notation to clarify

29. Working with Sig Digs • RESULTS NEVER HAVE MORE SIG DIGS THAN YOU STARTED WITH • Do the math first: • Add/subtract: perform operation and then round to lowest decimal sig figs that you started with • Multiply/divide: perform operation and then round to lowest total sig figs that you started with Write 4 numbers on a piece of paper and trade it with your neighbor- decide how many sig digs

30. The bottom line on sig digs: Don’t write out everything your calculator displays!!! Your answer should only include the sig digs.

31. Review • You have 2 measurements: A=1.24m and B=0.23cm • Which has more sig digs? • Which is more precise?

32. Review • You put your backpack on a scale and find that it weighs 14.2kg. What is the range of weights implied by this measurement? How would you write that? • 14.2+.05kg (1/2 of the smallest division of measurement)

33. Graphs • Remember the basics of experiments? • Independent variable is manipulated • Dependent variables change as a result • Graph independent vs dependent

34. Linear relationships • y=mx+b • Slope=m= y/ x • Remember + slope is up to the right, • -slope is down to the right

35. Nonlinear relationships • Quadratic- when one variable depends on the square of another- y=ax2+bx+c • Inverse- when y variable depends on 1/x

36. Practice: graphs • Practice problems p. 18 # 24