Straw Test Report

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Table 8. Average & standard deviation of shared data

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Result

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Figure 1. Plot from Obtained Data with Error Bar

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Figure 2. Plot from Outside Data with Error Bar

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Figure 3. Plot of All Data

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Discussion

Prior to the test, three group members are in charge of three different lengths of straw cutting and pinning separately. When performing the experiment with the test machine, the group is divided into three for three different lengths in order to increase the efficiency. It was agreed by the group that the error of the fit should be used when determining the failure load of the truss. Since it’s not the how the data points are scattered about the mean that is relevant but the range of values that the true mean is likely to occupy[1]. Comparing to the error bars in the plot, the error of the fit is very small.

Outside data of three different lengths of straws are obtained from another group. By inputting the three new lengths into the line fit, the difference in recorded buckling load and theoretical results can be calculated. There were discrepancies between two results, the major reason is suspected to be human errors from both groups when measuring the data.

While there are two variables of the measurement (repetition and number of source) can be controlled, it’s believed by the group members after discussion that by increasing the number of lengths tested will result a more certain estimate of buckling load versus length. Generally, there’s little doubt that systematic repetition constantly reduces errors in experiments, but that only provides a more accurate mean. Whereas having multiple lengths to test provides more points on the graph and a better curve fitting.

The method that was used in the analysis adopts mean and standard deviation, which reduces the variations in resulted by human error and other deficiencies. Echoing with preferable measurement discussed in last paragraph, all the class data with various lengths can cover a significant number the discrete points on the graph, and a more accurate linear relationship between bulking load and straw length.

Conclusion

Through the experiment and analysis, we get the equation y = -1.466x+ 32.00. In the processing of collecting data during experiment and calculating the data after lab, accuracy is always important. The buckling strength for straws will have a significant impact on the following steps of the project. By using this function, the buckling strengths of straws with different lengths can be obtained, which are foundational to determine the failure load for truss.

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