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== Initial Setup == === Mass Positioning === To begin we must have at least an idea of where to position the small mass. The large mass must also be placed such that it is in a similar position to the small mass at the opposite end such that the air resistance is similar from velocity. Ideally the masses should also have an identical cross sectional area for the same reason but the uncertainty introduced in the experiment due to this is hopefully small enough to not affect results. The small mass and large mass positions can be placed using trial and error or by using the calculation outlined in the [[Theory]] section. By positioning the large mass such that it touches a knife edge pivot, the small mass can be set somewhere around 2-4cm from the opposite knife edge. This seems to be a good positioning for the large mass. A decision of how the position of the small mass is going to be measured must be made. The value of the measurement is relevant only to the other small mass position measurements but it's precision will affect the fit precision and ultimately the final result. By measuring from the bottom of the small mass, in the small mass up (SMU) orientation, to top flat portion of the closest knife edge, a digital caliper can be used as a precise measuring device. It is important to note, however, that the small mass can slide and pivot slightly even when tightened very well so it is very easy to over estimate the measurements precision. === Wall Mounted Bracket === The wall bracket, which supports the pendulum as it swings, must be mounted firmly on a solid structure. It must be level in both the x and y planes (taking z as up and x as the direction of desired oscillation). If the bracket is not level, the pendulum can "walk" very minutely which can prolong y oscillations which introduce error into the measurements. These oscillations can be practically undetectable to the naked eye. === Period Measurement === [[File:CNUPendulum.jpg|thumb|40px]] A photo-gate is a good way to measure periods of the pendulum as it swings. Considerations for the photo-gate include a rigid base for it to stand on, what part of the pendulum is breaking the beam, and what software is interpreting the photo-gate signal. A solid base is necessary so that movement around the apparatus and natural vibrations of the lab do not cause unwanted motion of the gate. Something other than the bar, which is approximately 2.5 cm thick, should break the photo-gate beam. A thin steel "needle" was fashioned to be attached to each end of the pendulum and can be seen in the image. This allows for much small oscillations meaning that the small angle approximation correction can be much smaller. Another point to consider is the distance from the pivot to the photo-gate. The angle of oscillation should be measured so that the data can be corrected for the small angle approximation. The distance the pendulum should be displaced can be calculated by: : <math>x = y \tan \theta </math> Where <math>y</math> is the distance from the pivot to the photo-gate, <math>\theta</math> is the desired angle of oscillation, and <math>x</math> is the horizontal distance the pendulum should be displaced '''at the height of the photo-gate.''' The software easily available at CNU for interpreting the photo-gates is DataStudio. DataStudio has a photo-gate pendulum setup but use caution as the software interpolates the period based on your reported pendulum thickness. This setting can be used as a rough estimate of the period but using the state setup and taking time from either the leading or trailing edge of the data spikes is preferred.
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