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Units and Measurement

Units and Measurement. Kinds of Units. Base Derived. Math and Units. SI Units – International System MKS (Base Units) Meter m Mass kg Time s. Derived SI Units (examples). Units. Derived Units Velocity = Distance /Time => Unit of Velocity is _____

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Units and Measurement

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  1. Units andMeasurement

  2. Kinds of Units • Base • Derived

  3. Math and Units • SI Units – International System • MKS (Base Units) • Meter m • Mass kg • Time s

  4. Derived SI Units (examples)

  5. Units • Derived Units Velocity = Distance /Time => Unit of Velocity is _____ Density = Mass/ Volume => Unit of Density is _____ Rule: You EXPRESS the quantity in terms of Mass, Kilogram and Second

  6. The Seven Base SI Units

  7. SI Unit Prefixes - Part I

  8. SI Unit Prefixes- Part II

  9. SI Unit Prefixes for Length

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

  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. 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. Example: Convert 789m to km: 789m x 1km =0.789km= _____?? 1000m

  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. Limits of Measurement • Accuracy and Precision

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

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

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

  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. 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 • WHY?

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