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Intro to Measurement

Intro to Measurement. Isn’t it just reading the ruler?. Where do the numbers come from?. The numbers used in science class are measurements of some aspect of the universe What does this require? A system to make sure everybody measures the same thing the same way. SI System.

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Intro to Measurement

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  1. Intro to Measurement Isn’t it just reading the ruler?

  2. Where do the numbers come from? • The numbers used in science class are measurements of some aspect of the universe • What does this require? • A system to make sure everybody measures the same thing the same way

  3. SI System • A system agreed upon by scientists to produce consistency in measurement • Based on some aspect of the physical universe that is easily verified and always constant • Length (meter): The distance light travels in a certain amount of time • Time (second): The amount of time it takes for a molecule to “vibrate” a certain number of times

  4. Base Units • Base Units are the fundamental measurements that we use to describe an object

  5. SI Base Units

  6. Derived Units • Base Units are the fundamental measurements that we use to describe an object • Derived Units are a combination of two or more base units • Some things can’t be described by only one unit • Ex: Speed measures the distance you travel and the amount of time it takes to travel that distance (meters per second)

  7. Why Units? • Units are required on (almost) EVERY number that we use in science class • Remember, numbers are measurements • What is it exactly that you are measuring? • Units will tell you this!!

  8. Components of Measurement • What is required for all measurements • Numerical quantity • Unit • Name of substance • For example, • 325.0 mL water Numerical quantity unit Name of substance

  9. How to Measure • Certain Digit: What part of the measurement do you know FOR SURE!! • Uncertain Digit: What is your best guess as to the actual value of the measurement • No measurement is exact – they are only as good as the tools we use and the person using those tools

  10. How to Measure We know FOR SURE that the line is between 5 cm and 6 cm, therefore, we have one CERTAIN DIGIT: 5.?

  11. How to Measure It looks to me that the line is about 70% (or 7/10) of the way from the 5 cm line to the 6 cm line. We now have one UNCERTAIN DIGIT 5.7 cm

  12. Certain vs. Uncertain Digits • The number of CERTAIN digits will vary, depending on the measuring tool used • There will ALWAYS be only one uncertain digit, which is an estimation of how far between the last certain digit and the next certain digit the actual measurement is

  13. We know FOR SURE that the line is between 7.7 cm and 7.8 cm, therefore, we have TWOCERTAIN DIGITS: 7.7? How to Measure

  14. How to Measure It looks to me that the line is about 20% (or 2/10) of the way from the 7.7 cm line to the 7.8 cm line. We know have one UNCERTAIN DIGIT 7.72 cm

  15. How to Measure Each line represents 0.01 g Definitely between 7.10g and 7.11g, so 7.10? About 50% of the way, so 7.105 g

  16. How to Measure Each line represents 0.01 g Looks to be almost exactly on the 7.16 g line 7.160 g

  17. Accuracy vs. Precision • Accuracy is the closeness of a measured value to the ACTUAL value • Precision is the closeness of a bunch of measured values to each other

  18. Accuracy vs. Precision Could measurements be precise, but not accurate? Accuracy & Precision “Incorrect Ruler” Scenario

  19. Accuracy vs. Precision • Accuracy is the closeness of a measured value to the ACTUAL value • Precision is the closeness of a bunch of measured values to each other • Precision can also refer to the number of decimals places / significant digits that a measurement contains • 8.568s has a higher degree of precision than 8.56s

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