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Does this make sense

  1. Dec 9, 2009 #1
    Four hundred years ago Sir Isaac Newton pointed out that Work equals Force times Distance. Work is the energy needed to carry a heavy load over the landscape. The weight of the load is the Force against gravity. Each step forward requires a small Distance upward and here is where the work is done. Indeed the old-as-dirt adage that "a pound on your feet equals five on your back" follows because on average feet move, say, five inches upward with each step forward. Meanwhile the pack moves but an inch upward in the process. Thus the Work needed to move one pound of footwear one step is five times the Work needed to move one pound of pack weight, because the feet are lifted five times the Distance the pack is lifted. At least that's how I figure it.

    I understand that work is only done when there is a force to resist it but will weight on you feet really wear you out on the end of a hike as much as fives times that weight in your pack?
     
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  3. Dec 9, 2009 #2

    berkeman

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    Welcome to the PF. So are you saying that pushing the weight on a cart with wheels on a level road requires no work?
     
  4. Dec 9, 2009 #3
    i dont know, i am just asking if weight on the feet will end up costing you more energy (proportional to the distance it is moved against gravity) than the weight added to a backpack.
     
  5. Dec 9, 2009 #4
    Hey buddy. I hope I'm qualified to answer your question...

    But yes you would be saving a significant amount of energy, not necessarily due to the increase in vertical height, as it is mostly to due with acceleration and deceleration, and the implications they bring. You realize, your feet have to stop and accelerate (quite quickly unless you want to trip,) to over double your body's speed in order to catch up and keep you upright. That stop and go would be difficult with any weight, but if you use the same weight and kept its inertia going at a relatively steady pace, it will seem much more effortless.

    All about mass x acceleration!
     
  6. Dec 9, 2009 #5

    arildno

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    Nope.

    Coriolis formulated "Work equals Force times Distance" , not Newton.

    And Coriolis did that just 180 years ago, in a paper from 1829 or so.
     
  7. Dec 12, 2009 #6
    thanks impavid
     
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