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course phy 231
Brief rotating strap and magnetsUses toy car, magnets, rubber bands, rulers
See also Pictures related to Straps and Toy Cars
Toy car and magnets
Uses toy car, magnets, rubber bands, rulers
Using one magnet to repel the other, which is attached to the car, use magnet separations 8 cm, 5 cm and 3 cm to propel the car. Measure how far the car then coasts for each separation. Sketch a graph of coasting distance vs. separation.
Use your graph to predict coasting distances corresponding to separations of 4 cm and 6 cm.
Give your data and your estimates:
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At 8 cm separation, the car drifted 12cm
At 5cm separation, the car drifted 28 cm
At 3cm separation, the car drifted 54 cm
I fiddled with changing e^x, and I got 150e^(-.325x) to fit my points pretty well. And using this graph for 4 and 6 cm displacement, I got:
For 4 cm separation estimation: 41cm
For 6 cm: 21.5 cm
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Because of the geometry of the magnets, the force function is fairly complicated. You won't find a simple function to model it. The exponential function does as well as most of the available options, but the force function is not exponential in nature.
Analysis:
Now assume that the car and magnet have mass 80 grams, and that the coefficient of rolling friction is .03.
What is the force of friction?
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For each trial, how much work is therefore done against friction as the car coasts to rest?
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We can assume that all the potential energy in the magnets, before release, ends up being dissipated against friction after the car is released.
For each trial, how much potential energy do we infer the system has at the instant of release?
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Sketch a graph of PE vs. the separation of the magnets. You will have three points.
Find the average slope between the first and second point, and between the second and third point. Be sure to detail your reasoning of the first slope, including all the quantities used to find the slope, with units at every step.
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What do you think your slopes represent?
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How much potential energy did the magnet system gain between your first separation and your second?
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How far are the magnets displaced between your first separation and your second?
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What therefore is the average magnetic force between these separations?
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Using the same reasoning, find the average magnetic force between the second and third separation.
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At what point after its release do you think the car reached its maximum velocity? What could you easily measure to obtain a reasonable prediction of the point at which this should occur?
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Good data. See my note, and the appended instructions for analysis.
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