Staple your papers together in the upper left-hand corner. Include the lab number and title. Lab 2: Acceleration Due to Gravity Don’t forget your name, lab partners, date, class, and section number. John Smith, with Steve Jones and Rob Brown June 21, 2013 General Physics Lab I Section 3 Purpose is clear and concise, so we can discuss the success of the experiment later. Additionally, the purpose wasn’t copied verbatim from the lab manual. Lab title is repeated. Title: “Lab 2: Acceleration of Gravity” Purpose: Each section of the lab is labeled. Boldface type helps the labels stand out from the text. Measure the acceleration due to gravity of a freely falling body near the Earth’s surface (g) using a Picket Fence and a Photogate. Data and Calculations: Below is a diagram of the apparatus for this experiment: Picket fence A neatly handdrawn, labeled diagram of the apparatus is shown. While not necessary for our purposes, it is a nice touch. Qualitative observations are reported. The distance vs. time graphs are parabolic (see attached graph), and the velocity vs. time graphs are linear. The purpose of the following data is to determine the acceleration due to gravity at the Earth’s surface. Purpose of the table is Tables are a quick and clear way to show your data. Original data is shown. * Trial 1 2 3 4 5 6 2 * C (m/s ) 4.907 4.899 4.796 4.905 4.905 4.910 stated. 2 ** g (m/s ) 9.814 9.798 9.592 9.810 9.810 9.820 Table heading has appropriate units. This is the data taken from the plot of distance vs. time. See attached graph for Trial 1. This column was calculated from the data taken in the lab from the equation g = -2 C. ** Discussion in this section is limited to how the data was handled. Save the rest of the discussion for the Conclusion. Inspecting the data shows that Trial 3 is significantly lower than the other five trials. We expect that the Picket Fence was tilted and fell through the Photogate at an angle, resulting in a lower value of g (see the Conclusion section for more information). Since that value is probably from an incorrectly performed trial, it has been rejected and the rest of the calculations ignore it. Sample calculations are shown and clearly indicated. The rest of the calculations were done in the lab notebook. Therefore, the minimum, average, and maximum values for the trials are: 2 Acceleration (m/s ) * Average* 9.810 m/s2 Minimum 9.798 m/s2 Maximum 9.820 m/s2 The average was calculated from: (9.814 m / s ) + (9.798 m / s ) + (9.810 m / s ) + (9.810 m / s ) + (9.820 m / s ) 2 g= Again, use tables. g = 9.810 m / s 2 2 2 2 5 2 From the maximum, minimum and average values, we get our best answer and uncertainty for the acceleration due to gravity: Statements of uncertainty are shown in table form. Acceleration due to gravity (g) Precision* Percent Error** (9.81 ± 0.01) m / s 2 0.1% 0.0% * The precision was calculated as follows: 0.01 m / s 2 Precision = × 100% = 0.1% 9.81 m / s 2 ** The percent error was calculated as follows (9.81 m / s 2 ) − (9.81 m / s 2 ) % error = × 100% = 0.0% 9.81 m / s 2 Results: Results and Conclusion measure the success of the lab based on the Purpose section above. Sample calculations are shown and clearly indicated. The Results section briefly restates the important results found in the Data and Calculations section. Figures of uncertainty are included. Arguably, this section could be combined with the Conclusion. From the data taken for this experiment, we determined that the acceleration due to gravity at the Earth’s surface is (9.81 ± 0.01)m/s2. The value was measured to a precision of 0.1% and a percent error with the accepted value of 9.81 m/s2 of 0.0%. Additionally, the accepted value lies within the uncertainty ± 0.01 m/s2 of the experiment. Conclusion: OOPS!! The data didn’t come out as expected! The conclusion discusses a reasonable and defensible way that this mistake was handled. The acceleration of gravity measured in this lab verified that the accepted value of g is 9.81 m/s2 to within the uncertainty of the experiment. Additionally, our measurement was precise, with a small uncertainty of 0.01 m/s2. In performing our calculations, it was noted the value of g in Trial 3 was unusually low compared to the other values. This is probably because the Picket Fence was dropped at an angle that increased the distance, and therefore the measured time, between dark and transparent bands. This results in a lower calculated value of g for this trial. Since Trial 3 was done incorrectly, we rejected the data from this trial and calculated our final result from the other five trials. This paragraph correctly argues why the result of Trial 3 was lower, rather than higher, than expected. Questions posed in the lab manual are completely and concisely answered in a few sentences in the Conclusion. There are two main sources of error in this experiment. First, there is air resistance present in the measurement. Secondly, it is difficult to make certain the Picket fence is dropped perfectly vertically every time. Both of these could contribute to the uncertainty of the experiment. However, since the uncertainty was small, they cannot have contributed much, except as explained for Trial 3. The distance vs. time graphs are parabolic because the motion is uniformly accelerated. Additionally, the velocity vs. time graphs are linear for the same reason. For Trial 6, the Picket Fence was thrown downward, but let go before it entered the Photogate. This does not change the acceleration, because the Picket Fence was still only under the influence of gravity as it fell through the Photogate. Graphically, this is because the slope of the velocity vs. time graph does not change, only the values on the graph change. The Conclusion, and the lab as a whole, is short and to the point, but still manages to be complete. The phrase “Economy of Words” should come to mind. Sources of error are discussed. Graphs can be attached to the end of the lab report as appendices. If you want, you may also include them in-line with the text of the Data and Calculations section if your word processor will let you. Distance vs. Time for Picket Fence Graphs should be a full page and should be clearly labeled. Labels should include a title, x-variable and y-variable with units in parenthesis, and scales on each axis. 0.4 0.35 y = 4.9070 x2 + 0.7776 x + 0.0002 0.3 Equation of best fit line is displayed. Distance (m) 0.25 0.2 0.15 0.1 0.05 0 0 0.05 0.1 0.15 Time (s) 0.2 0.25
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