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course Phy 231
12/06/2011 @ 9:05p.m.
Oscillating Candy Bar
You suspended a candy bar from a rubber band chain and counted its oscillations for a minute. You did the same for a stack of 2 dominoes, and for a stack of four dominoes.
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The lab was very simple; I constructed a rubber band chain six bands long with a total length of 39cm. I then hung a Snicker’s bar from the chain and began gently oscillating the chain to maintain a constant rate of oscillation. I did this for 1 minute, and counted the number of oscillations. I then hung 4 dominos from the chain, then 8 dominos from the chain and measured the change in length.
Snickers: 80 oscillations/minute
4 Domino Length: 50 cm
8 Domino Length: 69 cm
Each Domino weights about 15.75g and adds about .86cm to the chain length
This means the chain stretches about .055cm per gram added.
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For each number of dominoes, determine the force constant k, based on your observations of the number of oscillations in a minute (which you can use to find the angular frequency omega) and the mass of the domino stack.
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For 4 dominos, I calculated k = 5,600 dynes/cm. For 8 dominos, I calculated k = 4,100 dynes/cm
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You don't say how you calculated this, but from two length vs. force points you can get only one value of k.
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Are your values of the force constant reasonably consistent?
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The values of K are within about 25% of one another. I believe this is due to variations in the masses of the dominos having a larger influence using less dominos.
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Based on your best estimate of the force constant and your observation of the frequency of the oscillations of the candy bar, what is the mass of the candy bar?
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If omega = 8.12 rad/sec (oscillations per sec converted to rad per sec), and K = 4100dynes/cm…then solving for m in the following equation gives us our mass.
8.12 rad/sec = sqrt.(4100dynes/cm / m)
M = 62g
According to nutrition facts, a bar has a mass of 57g, so I was off by about 9%...which doesn’t seem too bad given the measuring tools.
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Yes, this one works out pretty accurately.
However your differing values of k should be reconciled.
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