Recently had a lab on Rotational motion and mass distribution (strange as it wasn’t covered in class yet), and there were a few questions I needed to answer. I’m doing my best to understand the lab and concept, and I was hoping that someone could possibly broaden my understanding and tell me if I am on the right track:(adsbygoogle = window.adsbygoogle || []).push({});

The lab consisted of an apparatus with rotating platform. Near the bottom on the spindle, there is a string that is attached to it and a hanging mass, which is here:

http://home.earthlink.net/~copper017/Class/Physics/lab/RotatingPlatform.jpg [Broken][/URL]

I performed 3 trials with different radius sizes R on the platform (first was 0.25m, second was 0.30m, and third was 0.35m) with a hanging mass that was 2.67kg. I noticed as the platform’s radius got larger, it took more time for the mass to fall, and the acceleration (a) became smaller. However, as the radius became larger, the moment of inertia (I) became larger. So the bigger the radius, the longer it would take for a rotating object to reach its moment of inertia, right?

Here are my calculations and lab questions:

1. Does the plot of R2 versus I pass through the origin? Why?The plot does not pass through the origin. Passing through the origin would suggest that there is no moment of inertia at a given moment during rotation.

2. Could you measure the distance the mass falls by counting the number of rotations the rod makes? Would this be a better way to measure the distance?It is possible to find the distance if the radius of the spindle is known and its circumference is found. The difference of the height of the mass would be equivalent to the circumference of the spindle multiplied by the number of rotations around the spindle. Directly measuring and subtracting the initial and final height of the mass during the experiment would be a simpler way of finding the distance that the hanging mass falls.

http://home.earthlink.net/~copper017/Class/Physics/lab/table-3.jpg [Broken][/URL]

http://home.earthlink.net/~copper017/Class/Physics/lab/chart-3.jpg [Broken]

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# Homework Help: Rotational Motion Lab

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