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See saws and fulcrum

  1. Oct 21, 2007 #1
    on a see saw when one person weighs much more than the other, does the heavier person need to move closer to the fulcrum to balance out the weight?
     
  2. jcsd
  3. Oct 21, 2007 #2
    Go to a park and try it.
     
  4. Oct 21, 2007 #3
    I am so sorry to ask such a dumb question. I have a medical condition which prevents me from being able to figure things out as well as I used to. Please forgive me.
     
  5. Oct 21, 2007 #4
    Thinking intuitively:
    Think about two people with equal weights. In this situation, obviously to make them balance each other on a seesaw they would need to be the same distance away from the fulcrum.
    Imagine then that one of those people (Let's say Person A) moves closer to the fulcrum (pivot). Which direction would the see saw move?

    Thinking mathematically:
    Torque = Force x r
    r being the distance from the pivot point.

    To make the seesaw balanced the torque by person A would have to be the same as the one for person B. If person A's weight is bigger, then what do you have to do to r to make it stay constant?
     
  6. Oct 22, 2007 #5
    It is not a dumb question and I did not mean to be insensitive to your medical condition. Much of basic physics can be revealed by simple experiment and I meant to suggest that. I don't know your limitations, but you might be able to find a simple object, for example a metal kitchen ladle, where one end has much more mass than the other (or the mass is more concentrated). Then try balancing it on your finger (or on a pencil or the edge of something). Is the balance point closer to the "heavy" end or the light one?
    Tom
     
  7. Oct 22, 2007 #6
    And, here is an applet that allows you to "play" with this sort of question. Many people find that trying something out makes the equations more sensible.
    http://www.walter-fendt.de/ph11e/lever.htm
    Tom
     
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