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Homework Help: Factors affecting acceleration in a pulley system

  1. Sep 29, 2009 #1
    1. The problem statement, all variables and given/known data
    My group in physics conducted a lab which is described below:

    The lab was to investigate a factor affecting the accel. of an object. We were supposed to change only one factor to see how acceleration would be affected. My group had decided to use a simple static pulley system with one side kept a constant mass and the other was used to change the masses and see how changing the mass on that one side affected acceleration
    with F=ma (which can be rearranged in the pulley situation to g(m2-m1)/(m1+m2)

    I am just now realizing that we might have also changed the force by changing the mass on one side of the pulley system and therefore changed two factors instead of one. Is this true?

    The data that we have is the time it took the side with changing masses to rise to a certain distance. Is there anything we can do to show how acceleration is affected by the change of masses?

    If we totally messed up the lab, does anyone have any recommendations on how we can use our data in the best way to answer the question: How does changing mass affect acceleration?

    2. Relevant equations

    F = ma ; g(m2-m1)/(m1+m2)

    Δy = vₒt + ½ at² ? (not sure about that one and if it can relate)

    3. The attempt at a solution

    I'll be honest, I don't know where to go with this information. I have been playing around with my data for a few hours now trying to figure out how to figure out if my group even did this lab the least bit correct. As of right now I am just using g(m2-m1)/(m1+m2) , and comparing that value (which i think is theoretical) to the experimental value of acceleration from the kinematic.

    Any and all help is appreciated. My group really messed up on this one and it is due tomorrow. I know, labs shouldn't be done this way, but I really am asking for help right now.
  2. jcsd
  3. Sep 29, 2009 #2


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    Homework Helper

    I would say force is a responding variable rather than a manipulated one, so no problem.

    Go ahead and calculate the acceleration resulting from your change of a mass.
    Use Δy = vₒt + ½ at²
    The Vo will be zero, so if you know how far the mass went up and the time it took, you can calculate "a" easily. Then check to see if g(m2-m1)/(m1+m2) predicted it correctly.

    Do you do any error estimation in your labs? The thing is measurements are never exact so you really should make some effort to see if your measured acceleration matches the predicted value "to with measurement error". You could estimate how accurately you measured the time and distance and do the calculations again with the highest and lowest values that fall within the range of your estimated measurement error. Then see if the range in the calculated acceleration overlaps the predicted acceleration value.
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