Lab: Measurement: Accuracy and Precision
When scientists collect data, they must determine the accuracy and precision of their measurements. Accuracy refers to how close the measured quantities are to the actual or true value. Precision refers to the closeness of each of the data sets to one another. To distinguish between these two terms, it is useful to think of a target and the position of the measurements on the target. If the measurements are clustered together but away from the center of the target, then we would say the measurements are precise, but not accurate. If the data hits the center on the target, the measurements are precise and very accurate, i.e. the values collected are close to the true value one should obtain. In today's lab, you will make measurements and perform calculations to the appropriate number of significant figures. You will then determine if your measurements are precise and/or accurate. Before doing this though, you will have several exercises that test your knowledge of significant figures.
Measurements
1. Below are data sets from three students who were measuring the length of a piece of string.
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Student A:
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Student B:
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Student C:
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8.2 cm
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5.2 cm
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6.1 cm
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8.4 cm
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3.4 cm
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5.9 cm
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7.9 cm
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7.2 cm
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6.2 cm
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a. The true length of the string is 6.2 cm. Which student(s) measurements is/are accurate?
b. Which student(s) measurements is/are precise?
c. Are any of the students' measurements both precise and accurate? Please explain.
2. Length
a. Fold a piece of notebook paper into eight uniform rectangles, and then cut them out. Take one of the rectangles and using a best guess, try drawing a 6.5 cm line on it without using any measuring device. Set this paper aside. Without looking at this piece of paper, try drawing another 6.5 cm line on 3 more rectangles. Now, using a ruler, measure the exact length of each of your lines to the appropriate number of sig figs, and record them in the table below.
b. Calculate the average of your results. To receive credit, you must show your work.
c. What is your percent error? Show your work.
d. Comment on the accuracy and precision of your measurements.
e. On the remaining 4 rectangular pieces, try again to draw a 6.5 cm line on each of them. Again, do not use any measuring device when drawing the lines and do not refer to previous drawings. When you have finished, again measure the actual length of the lines and record your results in the table below.
f. What is the average and percent error of your measurements? Again, work must be shown to receive credit.
g. How do your results compare to your first set of measurements? Which set is more accurate? More precise? Please explain.
3. Time
a. Using a stopwatch, close your eyes, and try to estimate the passing of 30 seconds. Record the actual time that has passed in the table below. Repeat this 3 more times.
b. What is the average and percent error of your measurements?
c. Did your accuracy improve with subsequent trials?
Attachment:- Measurement_Accuracy_and_Precision.pdf