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Atwood Machine Lab

  1. Jan 30, 2016 #1
    1. The problem statement, all variables and given/known data
    I am given the equation (m1 – m2)g = (m1 + m2 + I/R2)a and the experiment is to validate this equation.

    2. Relevant equations

    3. The attempt at a solution
    After following the lab guide, it tells you to plot the weight difference (m1– m2)g against acceleration and determine the slope and y-intercept.

    If my graph is correct, than my equation is: y = 34.3x + 56.409

    And from here we are asked to solve for I (moment of inertia of the pulley). It also tells us that the equation predicted a zero y-intercept, however a non-zero is expected. why?

    I have no idea what to do with the slope or y-intercept in this situation. I was hoping for the radius of the pulley, but that is not given to us, nor is the mass of the pulley.

    Please Help.
  2. jcsd
  3. Jan 30, 2016 #2

    Simon Bridge

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    You have t think about what the equations are telling you about the physics ... when a=0, this is a constant speed.
    What does the theory tell you needs to happen for a=0, and what does your experiment tell you?
    Hint - look at the relationship between m1 and m2.

    Did you have the option to measure the dimensions of the pulley?
  4. Jan 30, 2016 #3
    The idea was that you would transfer a dime from one mass to the other to get an increased acceleration from one trial to the next. It accelerates the system twice the weight on the dime faster as its removed from one and placed on the other, so the mass of the system is always constant. Now sure how that relates to the rest... As for the pulley, no I don't have that option as I do not have the lab kit anymore - just going off of data I collected
  5. Mar 29, 2016 #4

    I'm working on a similar lab. Did you happen to get a negative value for your moment of inertia?
  6. Mar 29, 2016 #5

    Simon Bridge

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    You should not get a negative moment of inertia for the pulley... if you did, then you misplaced a minus sign somewhere.
  7. Mar 29, 2016 #6


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