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4th Class Levers?

  1. Jun 9, 2014 #1
    I'll assume that we all know of 1st, 2nd and 3rd Class Levers.

    Years ago I saw a brief remark in a magazine that I was browsing at the supermarket.

    It said that there was an obscure "4th Class Lever"—essentially what you get with a whip where the relative lengths of the Lever Arms are constantly changing and one end is accelerated far faster than the traditional levers would allow.

    {The book was purportedly discussing the Physics of Martial Arts and he was supposed to be applying the principle of the 4th Class Lever to whipping punches like a flicking backfist...

    Relatively few Martial Arts writers also have PhDs in Physics—so maybe the Dude was in error...}

    Anyway, I've never come across reference to 4th Class Levers—although an instructor at a Trade School who had a Masters Degree in Mechanical Engineering said that he Thought that there were several Obscure Levers that seldom get discussed.

    Anyone seen a Mathematical Treatment of 4th Class Levers?

    Have you even heard the term before?


    Saxon Violence
  2. jcsd
  3. Jun 9, 2014 #2


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    The lever classes are classified by the relative positions of the applied force, the fulcrum, and the resisting force. By symmetry...there is only 3 possibilities for these 3 things. How would you classify a 4th?
  4. Jun 9, 2014 #3
    You may be right.

    Nonetheless—lets imagine a teeter-totter with a 1:1 Mechanical Advantage, Lever at the rest position.

    However the Fulcrum is also a roller on a cam and when you lift, the relative position of the Fulcrum changes. The farther you lift the load the greater your Mechanical Advantage grows.

    Just to make it interesting, the Rate that the Mechanical Advantage grows increases exponentially with the distance the work end of the Lever has moved.

    Up to some sort of practical limit—otherwise you'd be dealing with Infinite Mechanical Advantage, Force or Velocity.

    Isn't that kinda what the end of a whip does as it is cracked?

    Saxon Violence
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