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Bloody Newton's 3rd law and the naughty lifter

  1. Aug 3, 2003 #1


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    You know what is lifter right. The tool you use to lift heavy objects.
    How does the 3rd Newton's law (action force = - reaction force) suit in it?What about conservation of energy?
  2. jcsd
  3. Aug 3, 2003 #2
    I can't tell what you're asking. By lifter, do you mean pulleys?
  4. Aug 4, 2003 #3


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    I mean something like the figure on:

    the fig is:coed.jpg
  5. Aug 4, 2003 #4
    I see what you mean, lever. I can't anwser though, I don't understand your question or what he is talking about in the paragraph above the picture, sorry.
  6. Aug 6, 2003 #5


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    Staff: Mentor

    It sounds like you have an idea here. So you tell us. What about conservation of energy?

    Or better yet, why even bother with energy? If you take a static view of a lever, there is no energy involved, just forces. Add 'em all up and they equal zero. Its pretty simple.
  7. Aug 6, 2003 #6


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    Re: Re: Bloody Newton's 3rd law and the naughty lifter

    I'll talk about the fug coed.jpg on my site:

    as it's obvious |Fa| <> |Fr| and |Da| <> |Dr| but...
    if you want to make |Fa|=|Fr| then you'll have to make |Da|=|Dr|
    it's so cause Ea = Fa x Da = Fr x Dr = Er.
    the equation Fa x Da = Fr x Dr means:
    smaller distance coresponds to larger force and
    larger distance coresponds to smaller force.

    Newton III is special case of my saying and it is when |Da|=|Dr|
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