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Move a Part at Constant Speed Under its Own Weight

  1. Nov 3, 2009 #1
    How can I make a hanging weight attached to a wire move at a constant speed under its own weight? The mass of the weight may vary and is not known beforehand.
  2. jcsd
  3. Nov 3, 2009 #2


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    Staff: Mentor

    Move where? What are the constraints on control? You haven't provided enough details for us to know what you are trying to do and what the constraints are.
  4. Nov 3, 2009 #3


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    Homework Helper

    My guess is to assume a frictionless environment. The question then becomes what is the shape of the curve that provides constant speed under the influence of gravity. The answer is a horizontal line, essentially eliminating any influence from gravity.

    If friction or aerodyanmic drag is allowed, than any straight line path will result in some terminal velocity, but initially the object will be accelerating.
  5. Nov 7, 2009 #4
    It is a little ambiguous what exactly is being asked. Constant velocity implies no net force, so your question makes me think about terminal velocity which is established through air resistance, or some sort of friction between the wire and something else. Alternatively, perhaps a counter weight of identical mass on the other side of a pulley is what your getting at.
  6. Nov 8, 2009 #5
    Ok. Sorry, you guys are right my first question was really vague. Here's a better description of what I'm trying to achieve. I want to design a wire apparatus that lowers a weight using the mass of the weight as the force, but then somehow achieves a balance of forces when the velocity reaches 1 m/s. This is simple enough using friction (I think), but the problem is that different weights will be put on this apparatus under different conditions, and the terminal velocity for each has to be 1 m/s.
  7. Nov 8, 2009 #6


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    Gold Member

    How about a variation of a flyball governor, wherein the flying weights have brake pad material on the leading edges and contact a surrounding cylinder? The faster it tries to fall, the more braking force is applied.
  8. Nov 8, 2009 #7
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