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Do Now & Announcements Grab a Handout (for after the quiz)
Turn in HW to be checked Clear desks and prepare for quiz Unit 1 Test MON 8/31
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Units *Unit= any standard that is used for comparison in numbers or measurement Whenever you report a measurement, you report a number followed by the unit
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System International (SI) Units: an international system of measurement based on the metric system. Some common ones we’ll be working with are: Measurement Base Unit Symbol Length meter Mass gram Volume Liter Temperature Kelvin Energy Joule Frequency Hertz Pressure Pascal Amount of Substance Mole Density grams/milliliter or grams/centimeter3 m g L K J Hz Pa mol g/mL or g/cm3
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Prefixes: placed before the base unit to indicate a larger or smaller quantity; based on powers of 10.
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x1000 x10 x10 x10 x10 x10 x10 x1000 x1000 Prefixes at the top of the chart represent a larger amount or quantity. Prefixes at the bottom of the chart represent a smaller amount or quantity.
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Accuracy vs. Precision
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Accuracy vs. Precision Accuracy=how close the results are to the correct answer (Bull’s eye!) To determine accuracy, we look at the average of our results. Precision= how often the same results are measured/obtained To determine precision, we look at the consistency of our results.
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AVERAGE ACCURATE NO
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each trial/measurement
precise NO
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Accuracy vs. Precision Practice
YES YES
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Accuracy vs. Precision Practice
4.67 NO 99 YES YES NO
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Percent Error A quantitative way we can look at the accuracy of a set of data if the true value is known For this class, we’ll say the data is accurate if the percent error is less than 5%
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The freezing point of water is 273. 2 K, but it was measured at 250
The freezing point of water is K, but it was measured at K. What is the percentage error? Calculate the top part first, then divide! ×100% 250.1− ×100%= =0.084×100% =𝟖.𝟒% NOT ACCURATE
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Percent Error Practice
2) 4.49 % 3) 888% 4) 3.88%
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Measurement: When using tools with graduated “tick marks”, you should estimate one decimal place beyond the value of the smallest tick mark! 0.7 cm Each tick mark represents 1 cm round to nearest 0.1 cm
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Each tick mark represents 0.1 cm
round to nearest 0.01 cm
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Reading Graduated Cylinders:
Liquids form a curved surface when in graduated cylinders. As a standard, you should read the liquid level from the bottom of the meniscus
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