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BellWork, Thurs 8/24

Explore the concepts of accuracy and precision through a hands-on experiment using a target, paper wads, and measuring tools. Calculate mean, median, mode, and percent accuracy to analyze results.

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BellWork, Thurs 8/24

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  1. Which of these pictures shows accuracy? Which of these pictures shows precision? BellWork, Thurs 8/24 D B A C

  2. Which of these pictures is most accurate? Which of these pictures shows precision? BellWork, Thurs 8/24

  3. The accepted value is 29.35. Which correctly describes this student’s experimental data? Bell Work Friday 8/25 A- accurate but not precise B- precise but not accurate C-both accurate and precise

  4. The accepted value is 29.35. Which correctly describes this student’s experimental data? Bell Work Friday 8/25 A- accurate but not precise B- precise but not accurate C-neither accurate nor precise

  5. Accuracy - how close a measurement is to the accepted value • Precision - how close a series of measurements are to each other ACCURATE = CORRECT PRECISE = CONSISTENT

  6. your value accepted value B. Percent Error • Indicates accuracy of a measurement

  7. % error = 2.9 % B. Percent Error • A student determines the density of a substance to be 1.40 g/mL. Find the % error if the accepted value of the density is 1.36 g/mL.

  8. Things you should know… • Mean:The average Equation: Add the values and divide by the number of values. Of the set of values 2, 6, and 7, the sum is 15. There are 3 values, therefore 15 ÷ 3 = 5; the mean is 5. • Median:The middle value in an ordered set of values Of the set of values 2, 6, and 7, the median is 6. • Mode:The most frequent value in a set of values Of the set of values 2, 6, and 7, there is no mode. Of the set of values 2, 6, 7, and 6, the mode is 6. • Range:The change or difference between extremes in a set of values Equation: Subtract the lowest value from the highest value. Of the set of values 2, 6, and 7, 7 – 2 = 5; the range is 5.

  9. Materials (per group) • 4 Paper Wads • Poster Paper • Tape • Meter Stick • Yarn, 20 cm • Marker

  10. Step One • Construct a target of 3 concentric circles around a center point (aka a bulls eye). • Measure a length of yarn and use the pen to mark distances 10, 20, and 30 cm from the end. • Tape the end of the yarn to the center point of the paper, but have one team member hold the yarn in place • Another student, keeping the string taut, rotates the string around the center point. • As the string moves, the third member of should trace the route of a mark on the yarn. The student repeats the process for each mark. Students can make a continuous line or points along the circle to connect after removing the yarn.

  11. Measure the distance between the closest edge of each paper ball and the center point of the target. Record under center.

  12. Calculations • Find the following for your team • Mean • Median • Mode • Percent accuracy: Number of hits to target ÷ total number of throws • Identify any outliers

  13. Exit:Questions to Answer • Which value represents accuracy: the mean, median, mode, or range from center • Which value represents precision: the mean, median, mode, or range from center • Was your team or an individual more accurate with each trial? Explain what contributed to becoming more or less accurate. • Was your team or an individual more precise with each trial? Explain what contributed to becoming more or less precise.

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