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Homework Help: Lab - elevator questions.

  1. Feb 2, 2004 #1
    I'm stuck on some lab questions I have to answer in my physics class.
    In the lab we held a spring scale in an elevator. We recorded his weight of the scale to be 9.5 newtons. We rode the elevator up and down and recorded the maximum and minimum readings on the scale. The maximum reading up was 11 newtons and the minumum was 8 newtons. The Maximum reading down was 10 Newtons and the minimum reading dwon was 9 newtons.

    1) Estimate the maximum acceleration and deceleration rates of the elevator from your results obtained using the spring scale.

    2) If the elevator cables broke and the safety brake failed such that the elevator's acceleration down is equal to "g", what should you expect the scales to read?

    3) If you measure or weigh an object or time an event here in the laboratory then we say that those measurements are conducted in the lab frame of reference. For most purposes we can consider the lab at rest or moving with uniform velocity through space. Galileo said these two conditions are equivalent and Newton said the results predicted by his laws are the same in either event. We see all reference frames moving with unifrom velocity inertial or Galiean frames. You just conducted an experimetn in a non-inertial frame--the accelerating or decelerating elevator. Discuss how this affected you perception of the gravitational field strength in the elevator.
  2. jcsd
  3. Feb 3, 2004 #2


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    I'll try to get you started without giving you the whole answer.

    consider what it is a spring scale measures:

    W = mg

    Now, draw force diagrams of the accelerating elevator, be sure to set up a consistent coordinate system, show the acceleration of the elevator and the acceleration due to gravity.

    The earth is exerting a force and the elevator is exerting a force, combine them to get something like f=(a+g)m.

    Note that you will need to consider your coordinate system to get the above equation correct. (ie, that + sign may not be what you want.)
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