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This Unit's

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History Lecture

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Lab

Parents' Notes

Natural Science Unit 6 Laboratory Activity:
Understanding Error in Experimental Data

Goal: To identify sources of error and understand propagation of error.

Materials and Equipment:

• A rectangular or square object
• A round object
• A cylinder (like a tuna or soup can)
• A ruler marked in centimeters or millimeters, or in ¹/₈ inches
• One or more helpful observers

Procedure:

1. Have each observer measure all four sides of your rectangular (or square) object. Record each measurement.
2. Have each observer identify the center of your circular object and measure its radius in at least three different directions from the center to the edge of the object. Record each measurement.
3. Have each observer measure the radius of your cylinder and its length.

Data Analysis:

• What is the greatest difference between your measurements of the same side of the rectangle? For example, if you have three measurements for the same side and they are 15.3cm, 15.5cm, and 14.9cm, the greatest difference will be between 14.9cm and 15.3cm, in the amount of .4cm. Note this value for each of the four sides that you measured.
• Using the smallest side measurements, calculate the area of your rectangle. For example, if you have a square and you use the 14.9cm measure for a side, your area will be 14.9cm * 14.9cm = 222.01cm*sup2;.
• Using the largest side measurements, calculate the area of your rectangle. For example, if you have a square and you use the 15.3cm measure for the side, your area will be 15.3cm * 15.3cm = 234.09 cm².
• Figure the difference for the area of the rectangle between your "high" measurements and your "low" measurements. In our example, the amount is 234.09 - 222.01 = 12.08cm²
• Figure the percentage error as a fraction using the difference divided by the smallest area. In our example, this would be 12.08cm² / 222.01cm*sup2; = 0.054 = 5.4%.
• Repeat your analysis for the circle you measured, calculating a maximum area, a minimum area, the difference, and the percent of error.
• Repeat your analysis for the cylinder you measured.

Report:

• Lay out your data in a well-organized table.
• Show at least one set of calculations, and the results of all calculations in the table.
• What are the sources of your errors in measuring?
• How could you reduce the amount of error and increase the precision of your measurements?

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