Lab Report 2_ Pendulum I - Frank Dong, Ayesha Minal, and Samantha Lattuca

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Feb 20, 2024

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Lab Report 2: Pendulum I Frank Dong Ayesha Minal Samantha Lattuca January 31, 2023 iOLab Unit #30 Introduction The purpose of this lab is to determine the factors that affect the period of a pendulum, specifically the angle of displacement. In this lab, we will construct a pendulum and perform a series of experiments on it. First, we will find the period of oscillation using a large and small angle, then, we will use our results to find the length of the pendulum using the equation that we derived from the pre-lab. Exercise 1: Measure the Period of Oscillation When the Angle of Displacement is Large E1 - Data Collection In this experiment, a simple pendulum (in which the mass is concentrated at the end point) was constructed using a metal lab stand, string, a weight, and a magnet. We were careful to ensure that the string was connected at a single pivot point on the lab stand to achieve the smoothest oscillations possible. The iOLab magnetometer was then turned on and calibrated in order to analyze the motion of the pendulum. Upon testing different orientations for placing the iOLab remote, we observed that our best data came from when the remote was placed +y orientation. Figure 1: Setting up the pendulum system Furthermore, before running the presented data, we used our phone timer to get a rough estimate of what the period of the pendulum should be around 1.5 seconds. That way, we had a base-level understanding of the values we should obtain. Finally, we recorded a set of many oscillations from the magnetometer sensor and acquired the following data. The data was then zoomed into until clear peaks in the magnetic field could be observed:
Graph was smoothed* Figure 2: Zoomed in data from magnetometer sensor showing clear peaks Using the cursor tool, we were able to determine the time during which each peak in the magnetic field occurred, which were reported in the following table: Peak Number Time (s) 1 1.12 2 2.65 3 4.26 4 5.71 5 7.32 6 8.85 7 10.38 8 11.91 9 13.46 10 14.99 11 16.52 12 18.05 13 19.58 14 21.11
15 22.65 Figure 3: Raw data reporting time and peak number in excel table E1 - Data Analysis From the excel data from Figure 3 the difference in time between each consecutive peak was calculated, giving us 14 measurements. The differences were calculated using the subtraction function on excel and not by hand. Moreover, an average period along with its uncertainty (standard deviation) were also found using excel functions. Peak Number Time (s) Differences (s) 1 1.12 2 2.65 1.53 3 4.26 1.61 4 5.71 1.45 5 7.32 1.61 6 8.85 1.53 7 10.38 1.53 8 11.91 1.53 9 13.46 1.55 10 14.99 1.53 11 16.52 1.53 12 18.05 1.53 13 19.58 1.53 14 21.11 1.53 15 22.65 St. Dev. Avg Period 1.53769231s 0.039613518s Avg Freq 0.65032516Hz Figure 4: Table showing differences in time between peaks
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The reported period from this method was found to be 1.5377 s +/- 0.03961 s Another method of finding the period was by using excel to generate a time of peak vs. peak number scatterplot. From this plot, a line of best fit was inputted, and its equation was included. Figure 5: Scatter plot with equation of line of best fit for time of peak vs. peak number (Experiment 1) The equation of the line of best fit was reported to be: y = 1.5371x - 0.3929 The slope of this line is another method for determining the average period of oscillation, which was found to be: T = 1.5371 s with no uncertainty. E1 - Conclusion In the end, both methods for finding the period of oscillation from a large angle displacement were successful, as both values were very similar to one another. The period obtained from method 1 was 1.5377 s +/- 0.03961 s and the period from method 2 was 1.5371 s. The values only differed by 0.0006 s (very minimal). Moreover, in the beginning when we measured the period using our phone timer, it was reported to be around 1.50 s. That was also close to our obtained periods, further validating this experiment’s success. Exercise 2: Measure the Period of Oscillation When the Angle of Displacement is Small E2 - Data Collection The same pendulum apparatus from Experiment 1 was used in this exercise. In this experiment, however, the pendulum was given a small angle of displacement, and the magnetometer sensor of the iOLab remote was tested at different orientations. We found that
our data was best when the remote was set up with the x-axis facing downward. The data obtained from around 40 s of oscillations resembled that of a sine wave: Figure 6: Frank setting up pendulum apparatus Figure 7: Magnetism and time sine curve Again, in this experiment, raw data was collected obtaining the time in which each peak occurred: Peak Number Time (s) 1 1.45 2 3.05
3 4.51 4 5.99 5 7.59 6 9.07 7 10.53 8 12.14 9 13.6 10 15.08 11 16.68 12 18.15 13 19.62 14 21.09 15 22.69 Figure 8: Raw data with peak number and time from Experiment 2 E2 - Data Analysis From the raw data table, a difference function from excel was used to determine the difference in time between peaks. Furthermore, the average and standard deviation (uncertainty) was calculated: Peak Number Time (s) Differences (s) 1 1.45 2 3.05 1.6 3 4.51 1.46 4 5.99 1.48 5 7.59 1.6 6 9.07 1.48 7 10.53 1.46 8 12.14 1.61 9 13.6 1.46
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10 15.08 1.48 11 16.68 1.6 12 18.15 1.47 13 19.62 1.47 14 21.09 1.47 15 22.69 1.6 St. Dev. Avg Period 1.51714286s 0.066033624s Avg Freq 0.65913371Hz Figure 9: Excel table showing difference in time between peaks on sine curve, as well as the average and uncertainty From this method, the period of oscillation when the angle of displacement is small was found to be T = 1.5171 s +/- 0.06603 s The other method for determining the period of oscillation was graphing a scatter plot from excel for time of peak vs. peak number. From there, a line of best fit was modeled along with its equation:
Figure 10: Scatter plot with equation of line of best fit for time of peak vs. peak number (Experiment 2) By this method, the slope of the line of best fit gave us the period of oscillation, which was found to be: T = 1.5124 s The obtained periods using both methods were similar to one another. In this experiment, another method for obtaining the period was by using the FFT function from iOLab, which was applicable because the curve appeared sinusoidal. We tested FFT values of 256, 512, 1024, 2048, and 4096. As it turned out, we collected enough data to use 4096: Figure 11: FFT function at 4096 for sine curve The reported frequency was 0.670 Hz, which can be converted to period using T = 1/f T = 1/f T = 1/(0.670 Hz) T = 1.4925 s Therefore, the period using this method was found to be 1.4925 s. E2 - Conclusion In the end, all three methods used to find the period of oscillation at a small angle of displacement were successful, the first two methods being more similar. By using the first method, the period obtained was 1.5377 s +/- 0.03961 s (Excel table), the second method (scatter plot) was 1.5124 s. The difference between these periods was about 0.03 s. The third
period (FFT) was 1.4925 s. The difference between the first period and third period is 0.045 s and the difference between the second period and third period is 0.02 s. Overall, all three methods led this experiment to being successful. Exercise 3: Calculate the Length of Your Pendulum E3 - Data Collection In this exercise, we used the period we obtained from exercise 2.2, which was 1.514 s to calculate the theoretical length of the pendulum. The formula T = 2π(L/g) ½ was rearranged to solve for T (as was done in the prelab). The theoretically determined and actual lengths of the pendulum were then reported and compared. Figure 12: Measuring the length of the pendulum E3 - Data Analysis L = (gT 2 )/(4π 2 ) = ((9.81 m/s 2 )*(1.514 s) 2 )/(4π 2 ) L = 0.5696 m Value of L using measuring tape: 57.912 cm = 0.58 m E3 - Conclusion The value of L was calculated to be 0.5699 m, and 0.58 m when it was physically measured with a measuring tape. These values are very close to one another, helping validate the experiment. Final Conclusion Overall, we were very successful in this lab as the values that we found experimentally and through calculations were very similar. We concluded that the equation we previously derived for the length (L) was accurate.The methods we used to calculate the period in both exercises were accurate as we ended up with similar results. In non-perfect conditions like this lab, some
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factors would affect our experiment such as air resistance. This results in the period being slightly inconsistent and decreasing the displacement. Another error we may have come across was the impossibility of maintaining a straight path in the pendulum’s motion, thus skewing our experimental data and creating uncertainty. If this experiment were to be performed again, we would make sure to try and maintain a straighter and more controlled motion.