Alternatively when allowing the string to unwind from

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string after each trial. Alternatively, when allowing the string to unwind from the hub, stop the hub from rotating just before the end of the string has been reached, so that the string doesn’t fall off of the peg. This will allow you to more easily rewind the string around the hub for each of your remaining trials. DO NOT tie the string to the hub, as this can cause the string to slip into the axle, and become permanently stuck.
9) Calculatethe mean of your ten accelerations. Then, use this mean to calculate an angular acceleration of the hub/platform (see Figure 13.3 and the Goals and Introduction for help thinking through this). 10) Measure and record the diameter of the hub using the caliper (or ruler if no caliper is present). Then, calculatethe radius of the hub, labeling it as r11) Using your driving mass and Equation 7, calculatethe torque that is being applied to the hub (we have already compensated for friction). 12) Now, using your torque, your angular acceleration, and Equation 6, calculatethe moment of inertia of the hub/platform. 13) Now, we will add a disk to the platform. Measure and record the mass of the disk (M) and the diameter of the disk. Then, calculate the radius of the disk, labeling it as 14) Calculate the predicted moment of inertia of the disk, Idisk, using Equation 8. 15) Calculate the predicted total moment of inertia when the disk is added to the hub/platform, using your calculated moment of inertia for the hub/platform, and your predicted value of the disk’s moment of inertia. Label this as Ipredict16) Place the disk on the platform. Using an analysis similar to one you just applied, determine the necessary driving mass to cause the hub/platform/disk system to rotate with an angular acceleration equal to your mean value found in step 9. Recordthe driving mass and label it as mhub2. 17) Measure and recordthe mass of the heavier of the two mass holders. Then, hang it from the free end of the cord as shown in Figure 13.2. Label this as mheavy18) Using the heavier mass holder, by trial and error, determine the amount of additional mass necessary to cause the hub to rotate with a constant velocity when the holder and the additional mass fall. Record the total mass (the mass of the holder and the additional mass added) necessary to compensate for friction now that we have added the disk to the platform. Label this as mf219) Add your driving mass, mhub2, to mf2and hang this total mass from the free end of the cord. 20) Hit the greenbutton on the top-center of the screen in LoggerPro and then release the mass/holder, allowing it to fall to the floor. Then hit the redbutton to stop the data collection. . R. . . .

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