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Why do we need to be able to measure things?

Learn how to make sense of measurements by incorporating both numbers and units, understanding precision and accuracy, and converting between units in the SI System. Master the basics of length, volume, and mass measurements.

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Why do we need to be able to measure things?

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  1. To make sense, all measurements need both . . . Suppose we wanted to measure a 2 x 4 for building a house. Numbers by themselves don’t make sense. Units by themselves don’t make sense. A Number and a Unit! A board is 350 long . . . . A board is meters long . . . . Any Ideas? Whydo we need to be able to measure things?

  2. Precision is a description of how close measurements are to each other. Accuracy is comparing your measurement to the actual or accepted value. Precision and Accuracy

  3. Length: measures distance between objects Volume: measures the amount of space something takes up Mass: measures the amount of matter in an object Other Types of measurement include: • time • temperature • density • PH Basic Types of Measurement

  4. Measurement System Comparisons All Measurement systems have standards. Standards are exact quantities that everyone agrees to use as a basis of comparison.

  5. This system works with any SI measurement. The UNIT becomes whichever type of measurement you are making. (mass, volume, or length) It is the same system regardless if you are measuring length, mass, or volume. The SI System uses the following prefixes:

  6. It works for all types of measurement. If you’re measuring . . . Length then it is the meter (kilometer, decameter, etc.) Mass then it is the gram (centigram, milligram, etc.) Volume then it is theliter (deciliter, hectoliter, etc.) centi gram The first part of the term indicates the amount, the second part indicates the type of measurement.

  7. Unlike the English system converting in the SI System is very easy. For Example in the English system if you wanted to know how many inches in 2 miles what would you do? Take the number of miles (2). Multiply it by the number of feet in a mile (5,280). Multiply that by the number of inches in a foot (12). How does converting units work? ANSWER: 126,720 inches in 2 miles

  8. For example in the metric system if you wanted to know how many centimeters were in 3 meters, what would you do? Find the unit you have (meters). Find the unit you are changing to (centimeters). Count the number of units in-between (2). Move the decimal point that many spaces, in the same direction you counted (right). The SI system is much easier. 3 meters = 300 centimeters Kilo Hecto Deca UNIT Deci Centi Milli

  9. More Conversions . . . 2,321.0 millimetersto meters = 2.321 meters 521.0 grams to hectograms =5.21 hectograms NOTE:The digits aren’t changing, the position of the decimal is. In the English system the whole number changes. Kilo HectoDecaUNITDeciCentiMilli

  10. Things to Remember • All measurements need a number and a unit! • Basic units of Measurement (meter, liter, gram) • How to convert metric units

  11. Length: measures distance between objects Volume: measures the amount of space something takes up Mass: measures the amount of matter in an object In SI the basic units are: • Length is the meter • Mass is the gram • Volume is the liter (liquid) • Temperature is Celsius Basic Types of Measurement

  12. Measurement Review • Measurements need a number and a unit! • Basic units of Measurement(meter, liter, gram) • How to convert metric units • Be able to make basic measurements of volume, length, and mass • Vocabulary words

  13. Conversion Factors Fractions in which the numerator and denominator are EQUAL quantities expressed in different units Example: 1 in. = 2.54 cm Factors: 1 in. and 2.54 cm 2.54 cm 1 in.

  14. How many minutes are in 2.5 hours? Conversion factor 2.5 hr x 60 min = 150 min 1 hr cancel By using dimensional analysis / factor-label method, the UNITS ensure that you have the conversion right side up, and the UNITS are calculated as well as the numbers!

  15. Sample Problem • You have $7.25 in your pocket in quarters. How many quarters do you have? 7.25 dollars 4 quarters 1 dollar = 29 quarters X

  16. A rattlesnake is 2.44 m long. How long is the snake in cm? a) 2440 cm b) 244 cm c) 24.4 cm

  17. Solution A rattlesnake is 2.44 m long. How long is the snake in cm? b) 244 cm Kilo HectoDecaUNITDeciCentiMilli

  18. Amount of People in the World. • There are 6,900,000,000 people in the world. • What is a better way to write this HUGE value? • Scientific Notation • 6.9 X 109 People • Why are we able to write the number like this?

  19. Significant Figures – long story short, this is how well you measured something. The most confusing parts are the zeros • Rules

  20. No decimal – trailing 0 – not sig. Ex: 7400 --- 2 sig. figs - zeros between nonzero are sig. Ex: 308562 --- 6 sig. figs Decimal ‹ 1– start from left, count all nonzero + zero between Ex: 0.00506 --- 3 sig. figs. Ex: 0.001400 --- 4 sig. figs Decimal › 1 – all count Ex: 40.070 --- 5 sig. figs

  21. How many significant figures are in the following: • 203.4 • 7600 • 0.000035

  22. How many significant figures are in the following: • 203.4 --- 4 Decimal › 1 – all count • 7600--- 2 No decimal – trailing 0 – not sig. - zeros between nonzero are sig. • 0.000035--- 2 Decimal ‹ 1 – start from left, count all nonzero + zero between

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