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Lab Issues


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So... it's sunday night and time for the lab questions! It seems to me that we need loggerpro to make the graphs, because otherwise how can we calculate net torque? For the Part I questions I used the formula we derived in class (I=1/2mR^2 for a thin disk rotating about its center) and the equation from the reading (torque=Ialpha) for all of the masses, which got me a nicely linear graph of net torque versus angular acceleration. I guess this proves that net torque is proportional to angular acceleration, which we already know. What I think the lab wants us to discover is that moment of inertia varies for each set-up, but for us to "discover" this we would need a way to calculate net torque without first finding moment of inertia. Plus, I have no idea how to get the moment of inertia for the trials with the two masses on the end of the rod. We haven't learned how to deal with non-uniform masses and I'm hoping Mr. Fullerton doesn't want us to start by deriving moment of inertia for this one! I did find a couple of lists of moments of inertia on wikipedia, but nothing dealing with uneven distribution of mass. Below is a pretty crazy one- I can't think of any scenarios where it would actually be needed, but the math looks intense. In short, I'll be going in early tomorrow and advocating for a later due date![TABLE="class: wikitable"]

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[TD]Infinite disk with mass normally distributed on two axes around the axis of rotation (i.e. 2aeebd23984647946377dcafbb1da41f.png Where : ρ(x,y) is the mass-density as a function of x and y).

[/TD]

[TD]958d1a48f5df2d9e750c2800edc91a82.png130px-Gaussian_2d.png[/TD]

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To find the net torque, recall that torque is force multiplied by distance when applied at a right angle. You know the radius of the disk, and the force applied (mg for your hanging mass)... use that to find your moment of inertia.

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