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Mastering Units and Measurement: A Comprehensive Guide

Learn the language of physics through SI units, prefixes, conversions, significant figures, and word problem solving. Understand the accuracy, precision, and limits of measurements to ace your physics class!

danacoleman
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Mastering Units and Measurement: A Comprehensive Guide

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  1. Units andMeasurement PhysicsMrs. Coyle International Space Stationhttp://apod.nasa.gov/apod/image/0706/iss_sts117_big.jpg

  2. It All Starts with a Ruler!!!

  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. SI Unit Prefixes - Part I

  5. SI Unit Prefixes- Part II

  6. The Seven Base SI Units

  7. Derived SI Units (examples)

  8. SI Unit Prefixes for Length

  9. Scientific Notation M x 10n • M is the coefficient 1<M<10 • 10 is the base • n is the exponent or power of 10

  10. Other Examples: • 5.45E+6 or • 5.45 x 10^6

  11. 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

  12. 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

  13. Factor-Label Method of Unit Conversion: Example • Example: Convert 789m to km: 789m x 1km =0.789km= 7.89x10-1km 1000m

  14. 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

  15. Limits of Measurement • Accuracy and Precision

  16. Accuracy - a measure of how close a measurement is to the true value of the quantity being measured.

  17. 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

  18. Precision – a measure of how close a series of measurements are to one another. A measure of how exact a measurement is.

  19. 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

  20. Example: Evaluate whether the following are precise, accurate or both. Accurate Not Precise Not Accurate Precise Accurate Precise

  21. Significant Figures • The significant figures in a measurement include all of the digits that are known, plus one last digit that is estimated.

  22. Centimeters and Millimeters

  23. 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.

  24. How many sig figs? 100 10302.00 0.001 10302 1.0302x104

  25. 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)

  26. 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)

  27. Counting Numbers • Counting numbers have infinite sig figs. • Ex: 3 apples

  28. 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?

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