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# PP2_-_2_Units_and_Measurement.ppt

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# PP2_-_2_Units_and_Measurement.ppt

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### PP2_-_2_Units_and_Measurement.ppt

1. 1. Units and Measurement Physics Mr. Berman International Space Station http://apod.nasa.gov/apod/image/0706/iss_sts117_big.jpg
2. 2. It All Starts with a Ruler!!!
3. 3. Math and Units • Math- the language of Physics • SI Units – International System – MKS •Meter m •Mass kg •Time s • National Bureau of Standards • Prefixes
4. 4. SI Unit Prefixes - Part I Name Symbol Factor tera- T 1012 giga- G 109 mega- M 106 kilo- k 103 hecto- h 102 deka- da 101
5. 5. SI Unit Prefixes- Part II Name Symbol Factor deci- d 10-1 centi- c 10-2 milli- m 10-3 micro- μ 10-6 nano- n 10-9 pico- p 10-12 femto- f 10-15
6. 6. The Seven Base SI Units Quantity Unit Symbol Length meter m Mass kilogram kg Temperature kelvin K Time second s Amount of Substance mole mol Luminous Intensity candela cd Electric Current ampere a
7. 7. Derived SI Units (examples) Quantity unit Symbol Volume cubic meter m3 Density kilograms per cubic meter kg/m3 Speed meter per second m/s Newton kg m/ s2 N Energy Joule (kg m2/s2) J Pressure Pascal (kg/(ms2) Pa
8. 8. SI Unit Prefixes for Length Name Symbol Analogy gigameter Gm 109 megameter Mm 106 kilometer km 103 decimeter dm 10-1 centimeter cm 10-2 millimeter mm 10-3 micrometer μm 10-6 nanometer nm 10-9 picometer pm 10-12
9. 9. • 9 min video about powers of 10 in length. • http://powersof10.com/film
10. 10. Scientific Notation M x 10n • M is the coefficient 1<M<10 • 10 is the base • n is the exponent or power of 10
11. 11. Other Examples: • 5.45E+6 or • 5.45 x 10^6
12. 12. Numbers less than 1 will have a negative exponent. A millionth of a second is: 0.000001 sec 1x10-6 1.0E-6 1.0^-6
13. 13. Factor-Label Method of Unit Conversion • Example: Convert 5km to m: • Multiply the original measurement by a conversion factor. NEW UNIT 85km x 1,000m = 85,000m 1km OLD UNIT
14. 14. Factor-Label Method of Unit Conversion: Example • Example: Convert 789m to km: 789m x 1km =0.789km= 7.89x10-1km 1000m
15. 15. Convert 75.00 km/h to m/s 75.00 km x 1000 m x 1 h___ = 20.83m/s h 1 km 3600 s
16. 16. Limits of Measurement • Accuracy and Precision
17. 17. • Accuracy - a measure of how close a measurement is to the true value of the quantity being measured.
18. 18. Example: Accuracy • Who is more accurate when measuring a book that has a true length of 17.0cm? Susan: 17.0cm, 16.0cm, 18.0cm, 15.0cm Amy: 15.5cm, 15.0cm, 15.2cm, 15.3cm
19. 19. • Precision – a measure of how close a series of measurements are to one another. A measure of how exact a measurement is.
20. 20. Example: Precision Who is more precise when measuring the same 17.0cm book? Susan: 17.0cm, 16.0cm, 18.0cm, 15.0cm Amy: 15.5cm, 15.0cm, 15.2cm, 15.3cm
21. 21. Example: Evaluate whether the following are precise, accurate or both. Accurate Not Precise Not Accurate Precise Accurate Precise
22. 22. Significant Figures • The significant figures in a measurement include all of the digits that are known, plus one last digit that is estimated.
23. 23. Centimeters and Millimeters
24. 24. Finding the Number of Sig Figs: • When the decimal is present, start counting from the left. • When the decimal is absent, start counting from the right. • Zeroes encountered before a non zero digit do not count.
25. 25. How many sig figs? 100 10302.00 0.001 10302 1.0302x104
26. 26. Sig Figs in Addition/Subtraction Express the result with the same number of decimal places as the number in the operation with the least decimal places. Ex: 2.33 cm + 3.0 cm 5.3 cm (Result is rounded to one decimal place)
27. 27. Sig Figs in Multiplication/Division • Express the answer with the same sig figs as the factor with the least sig figs. • Ex: 3.22 cm x 2.0 cm 6.4 cm2 (Result is rounded to two sig figs)
28. 28. Counting Numbers • Counting numbers have infinite sig figs. • Ex: 3 apples
29. 29. Solving Word Problems • Analyze – List knowns and unknowns. – Draw a diagram. – Devise a plan. – Write the math equation to be used. • Calculate – If needed, rearrange the equation to solve for the unknown. – Substitute the knowns with units in the equation and express the answer with units. • Evaluate – Is the answer reasonable?