In this experiment we will use rotational tables with shaft encoders on them.
The software is EncoderAD4.exe downloadable from the Resource page or here.

One wants to determine the moment of inertia of the disc assembly in this experiment.

• the diameter of all discs seems to be 254 mm, or 10.0 inches
• the mass of the dark plastic discs by themselves is around 843 g
• the aluminum assembly with (I assume) a brass shaft is about 78 g
• a dark disc plus shaft assembly has a mass of 926 g plus or minus about 3 g
• the diameters on the aluminum piece seem to be 3.0, 4.0 and 5.0 cm
• the mass of the rectangular iron piece is about 707 g.

The plan is

• use a string wrapped around one part of the axle and connect the string via a pulley to a hanging mass
• make an estimate of the drag torque in the apparatus
• by taking data as the wheel coasts to a stop
• by averaging data between mass falling and mass climbing
• take data for 3000 points using program EncoderAD4
• from this determine the angular acceleration
• do this from the angular velocity, time graph [what kind of fit?]
• also do this from the angle, time graph [what kind of fit?]
• check out one radius fully before trying the second radius, two trials.
• If time permits, do two two trials at a second radius

alpha  = mgr/(mr^2 + I), where m is the hanging mass, and r is the radius of the point of application of the force. (We used this for the bicycle wheel data.)

• measure alpha and calculate I from it
• for each r, calculate I the moment of inertia of the large plastic disc with aluminum assembly
• this disc has a mass around 900 g and a radius around 127 mm, with a thickness of 12 mm or so
• calculate I for the disc from mass and radius.
• if you do things right there will be a discrepancy of more than a factor of 2 between I from the acceleration and I from the mass and radius
• knowing this, try to figure out where such a discrepancy could arise (last year we had problems with the program, but now those problems are repaired)

• Try hard to keep the write-up to 1 1/2 hours or less.
• Err on the side of giving me something a little crude.
• Make yourself stop after 1 1/2 hours and turn in what you have so I can comment on it, even if it is not finished
• Give a few sentences (up to 5 or so) generally describing what went on in the experiment.
• Make a sketch of the apparatus (don't make it tiny)
• State what you did
• Give a brief phrase saying what each step was
• Include data, with units. Make sure it is clear where the data came from.
• Analyze the data. In this case you wish to calculate I from your data.
• Give one sample calculation, so I can see your numbers and units.
• Give an estimate of how good you think the answer is (within 5% of the truth? 2%? 10%)
• If you can support this estimate, please do that
• Explain the original discrepancy between the I values, and how you straightened it out.