Record these in your lab journal next you will need

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Unformatted text preview: obtaining results is the only reliable way to take data. How else can you know if something has gone wrong? This happens so often that it is given a name (Murphy’s Law). It is also a good way to make sure you have learned something, but only if you stop to think about the discrepancies or similarities between your prediction and the results. In order to enter your prediction into the computer, you first need to decide on your coordinate axes, origin, and scale (units) for your motion. Record these in your lab journal. Next you will need to select the generic equation, u(t), which describes the graph you expect for the motion along your x-axis seen in your video. You must choose the appropriate function that matches the predicted curve. The analysis program is equipped with several equations, which are accessible using the pull-down menu on the equation line. The available equations are shown to the right. You can change the equation to one you would like to use by clicking on the arrows to the left of the equation After selecting your generic equation, you next need to enter your best approximation for the parameters A and B and C and D where you need them. If you took good notes of these values during the filming of your video, inputting these values should be straightforward. You will also need to decide on the units for these constants at this time. Once you are satisfied that the equation you selected for your motion and the values of the constants are correct, click "Accept" in the Main Controls. Your prediction equation will then show up on the graph on the computer screen. If you wish to change your prediction simply repeat the above procedure. Repeat this procedure for the Y direction. DATA COLLECTION 217 APPENDIX: SOFTWARE To collect data, you first need to identify a very specific point on the object whose motion you are analyzing. Next move the cursor over this point and click the green ADD Data Point button in Data Acquisition control box. The computer records this position and time. The computer will automatically advance the video to the next frame leaving a mark on the point you have just selected. Then move the cursor back to the same place on the object and click ADD Data Point button again. So long as you always use the same point on the object, you will get reliable data from your analysis. This process is not always so easy especially if the object is moving rapidly. The data will automatically appear on the graph on your computer screen each time you accept a data point. If you don’t see the data on the graph, you will need to change the scale of the axes. If you are satisfied with your data, choose Quit Data Acq from the controls FITTING YOUR DATA Deciding which equation best represents your data is the most important part of your data analysis. The actual mechanics of choosing the equation and constants is similar to what you did for your predictions. First you must find your data on your graphs. Usually, you can find your full data set by using the Autorange buttons to the left of the graphs. Secondly, after you find your data, you need to determine the best possible equation to describe this data. After you have decided on the appropriate equation, you need to determine the constants of this equation so that it best fits the data. Although this can be done by trial and error, it is much more efficient to think of how the behavior of the equation you have chosen depends on each parameter. Calculus can be a great help here. Lastly, you need to estimate the uncertainty in your fit by deciding the range of other lines that could also fit your data. This method of estimating your uncertainty is described in the appendix Accuracy, Precision and Uncertainty. Slightly changing the values for each constant in turn will allow you to do this quickly. For example, the X-motion plots below show both the predicted line (down) and two other lines that also fit the data (near the circles). 218 APPENDIX: SOFTWARE After you have found the uncertainties in your constants, return to your best-fit line and use it as your fit by selecting Accept x- (or y-) fit in the Program Controls panel. LAST WORDS These directions are not meant to be exhaustive. You will discover more features of the video analysis program as you use it. Be sure to record these features in your lab journal. 219 APPENDIX: SOFTWARE MAGNETLAB - MEASURING CONSTANT MAGNETIC FIELD Application Basics Before you begin, you should ensure that you have read the relevant sections of Appendix A to familiarize yourself with the equipment. The software package that works in tandem with your magnetic field sensor is written in LabVIEW™. It allows you to measure and record magnetic field strength as a function of a number of different variables. After logging into the computer, execute the application by double clicking the “MAGNETLAB” icon located in the PhysLab folder on the desktop. Before you start using the program, you should take a moment to identify several key elements. The two most important of these are the Command Panel, shown to the right, and the Guide Box, shown bel...
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This document was uploaded on 02/23/2014 for the course MANAGMENT 2201 at University of Michigan.

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