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

Bloody Newton's 3rd law and the naughty lifter

  1. Aug 3, 2003 #1


    User Avatar

    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


    User Avatar

    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


    User Avatar

    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


    User Avatar

    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|
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?

Similar Discussions: Bloody Newton's 3rd law and the naughty lifter
  1. Newtons 3rd law (Replies: 4)

  2. Newton's 3rd Law (Replies: 17)