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Homework Help: Some help with a circular motion lab

  1. Oct 6, 2006 #1
    First off, I obtained results that were way off. We were to study the effects of force, mass, and radius on the frequency of a spinning object.
    We were supposed to obtain slopes of 1/2 for the graph of each relationship, my radius graph was pretty good(0.56), my force graph wasn't very good(0.08), and my mass graph, to be honest, was a complete disatser, I somehow obtianed a slope of 30. I could understand it being a little mroe off then the others because it was the end of the period, and everyone was rushing to get the data, but the result was 60 times as much as it should be, which I found completely ridiculous, I even checked over my work, and everything seemed alright, the final answer was way off. Can anyone suggest why my answer might've been so far off? I can post my work, if you want.

    Second, this part has me stumped. We have to explain how the experiment displays each of Newton's laws. I'll explain exactly we did the experiment:

    We had a tube that we put a string through, at one end of the string, we tied rubber stopper(s), and the other end had weights attached to increase the tension. We had to swing the rubber stopper around, and then figure out frequency from timing how long it took the stopper to make 20 complete cycles.

    For Newton's first law, I said something along the lines of this:

    The object does not have a net force of zero acting on it, so by Newton's first law, it should be accelerating(not having a constant velocity). It is known that the object does not have a net force of zero acting on it because it is constantly changing direction.

    I'm not sure if that's the best way to put it, but that's what I have.

    Newton's second law:

    The object is always accelerating towards the centre, which is in the same direction as the force, thus demonstrating Newton's second law.

    Newton's third law:

    I had no clue how to explain this. What reaction forces are going on here? of course there's going to be reaction forces, but I didn't think that any would really contribute to the understanding of the system very well.
  2. jcsd
  3. Oct 6, 2006 #2


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    It would be useful to look up the definition of tension
  4. Oct 7, 2006 #3


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    Did you draw a graph of frequency (dependent variable) against radius (independent) and got a gradient of 0.5?

    For N1 I would think it is more correct to reason along these lines: The direction of the velocity of the stopper is always changing so we can conclude that it is accelerating. This means that a resultant force is acting on it.
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