Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Distance amplifiers

  1. Sep 9, 2006 #1
    Question: Just as there are block & tackle that amplify weight handling, for example, a man pulls down on a rope with 10 lbs of force and lifts 100 lbs as a result: Are there mechanical devices that amplify distance? E.G. a man moves down a 100 lbs weight 4 feet and thereby moves upward a 10 lbs weight 8 feet or 10 feet or 12 feet, etc. The block & tackle system sacrifices distance for weight amplification. The distance amplifier sacrifices weight for increased distance?
    Anything in classical mechanics or Newtonian physics that has been overlooked?
  2. jcsd
  3. Sep 9, 2006 #2


    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    The lever: Put the fulcrum nearer the end of the effort arm. You get a mechanical advantage < 1, but a velocity ratio > 1.

    Gears: Ever ridden a multiple gear bicycle on a high gear ratio?
  4. Sep 9, 2006 #3


    User Avatar

    Staff: Mentor

    Or take your block and tackle and swap the ropes that the man and the load are attached to.
  5. Sep 10, 2006 #4
    in all cases, energy is conserved...
  6. Sep 11, 2006 #5


    User Avatar
    Science Advisor

    In a sense, the same block and tackle (lever and fulcrum, screw, ramp, i.e. all simple machines) that "amplify" force also "amplify" distance. Unfortunately, because energy= force*distance is conserved to do one, you have to "undo" the other. If I hoist a weight using a block and tackle with n "lines", I only have to apply force equal to 1/n times the weight but I only lift it 1/n times the distance I pull. If I attach the weight to the end I was pulling on and go pull on the other end (what jtbell said), I reverse that: I lift the weight n times the distance I pull, but I have to apply n times the weight in force.

    Similarly, as Gokul43201 said, using a lever "the wrong way around" will "amplify" distance moved at the cost of using addtional force.
  7. Sep 11, 2006 #6


    User Avatar
    Gold Member

    This is also the basis of most hydraulics in heavy construction equipment, the 'Jaws of Life' and other such devices. The cylinder might have a stroke of only a foot or so, but moves the load 10 feet. Hydraulics have such enormous force that the trade-off is acceptible.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook