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Units and Measurement

Units and Measurement. Physics Mrs. Coyle. International Space Station http://apod.nasa.gov/apod/image/0706/iss_sts117_big.jpg. It All Starts with a Ruler!!!. Math and Units. Math- the language of Physics SI Units – International System MKS Meter m Mass kg Time s

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Units and Measurement

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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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