Lab1 Experimental Errors and Uncertainty Worksheet

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Pueblo Community College *

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111

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Mechanical Engineering

Date

Feb 20, 2024

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docx

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3

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Lab 1: Experimental Errors and Uncertainty – Informal Report Worksheet Name: Ashley Gulick Date: 01/26/24 Pre-Lab Questions 1. Explain the difference between accuracy and precision. Answer: The difference between accuracy and precision is that accuracy is a measured quantity that measures how close results are to the exact or true value and precision measures how close measurement results are to one another. 2. Name a statistical quantity that can be used to indicate an accuracy level. Answer: A statistical quantity that can be used to indicate an accuracy level is to compute the percent error between the average measurement and an accepted or theoretical value. 3. Name a statistical quantity that can be used to indicate a precision level. Answer: 4. To what level of accuracy (1 cm, 0.1 cm, 0.01 cm, 0.001 cm) can the ruler used to measure the lengths of the pencil in Table 1 of the Lab 1 Instructions Sheet be read? Answer: Post-Lab Questions Part 1 A student measures the value of the acceleration due to gravity several times and obtains the following results (all in m/s 2 units): 9.95, 10.10, 9.97, 9.99, and 10.02 Given: The accepted value for the acceleration due to gravity on Earth is 9.81 m/s 2 .
PHY 1111 Lab 1 Worksheet 1. Determine the uncertainty range for this set of data, using any calculation tool at your disposal. Please record the uncertainty range here with appropriate significant figures and units as discussed in the above pages. Answer: 2. Determine both the accuracy and precision levels in percentage form. Show your work here. Answer: 3. Do random errors alone seem to account for any inaccuracies from the accepted value, or does a systematic error appear to be present? Explain your reasoning. Answer: Part 2 We may not always be able to determine an accuracy level using a percent error calculation when an accepted value for a quantity is unknown. However, if we have multiple ways of determining a quantity, such as independent measuring methods or theories, we can compare two different results for the same quantity using a percent difference. Comparing the uncertainty range between the two methods is very useful as well. Later on in Module 2, we will study frictional forces along with coefficients of friction which are unitless numbers that describe the amount of friction between various surfaces. Let us compare a set of measurements for a friction coefficient between a wooden and rubber surface using two different methods of measurement: a simple pulling technique, and an incline sliding technique. Here's the data: Coefficients of Friction between wood and rubber surfaces Direct Pulling Method Incline Plane Method 0.72 0.71 0.70 0.91 0.79 0.66 0.74 0.79 0.75 0.87 1. Complete the values in the table for the uncertainty ranges and precision levels for each set and find the percent difference between the two sets. Show your worked out calculations below.
PHY 1111 Lab 1 Worksheet Coefficients of Friction between wood and rubber surfaces Direct Pulling Method Incline Plane Method 0.72 0.71 0.70 0.91 0.79 0.66 0.74 0.79 0.75 0.87 Uncertainty Range Precision Level (%) Percent Difference 2. Which data set seems to be more reliable and why? Does this set have less random or systematic error? Answer: 3. Given the percent difference between the two sets, do you think the two sets provide a statistical different value for those coefficients, or do you think they are statistically the same? Use the uncertainty ranges to help explain this. Answer: 4. Comparing the two uncertainty ranges, does any of the data appear to be suffering from any systematic effects? Why or why not? Answer:
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