1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: Force acting on a pivot

  1. Jul 19, 2011 #1
    Hi there,
    I have a two part question, just for my understanding not homework. Say you had a see-saw type lever like in my attachment. The yellow ball represents a 1N force and the green 2N and they are both 1m from the pivot. The blue bar is a beam attached hanging down directly off the lever so that it keeps the lever perfectly horizontal. My questions are:

    1. What force does the blue bar exert on the red support? (My guess is 1N to the left.)
    I think i'm confusing myself because it's directly under the pivot and therefore i'm thinking it has no torque, but surely it is exerting a force?

    2. What force is exerted down on the pivot? (My guess is 3N straight down.)
    But my thinking is maybe the red support is taking some of the load off the pivot so maybe less than 3N?

    Any help is appreciated, i'm an absolute novice trying to teach myself with an old textbook.

    Attached Files:

  2. jcsd
  3. Jul 19, 2011 #2
    got 1) you should know how to play with torque :)

    its obvious that the blue and red bar will meet at a point (ad not a surface) ... calculate the distance of this point from the pivot ... the force due to this contact provides restoring torque such that it balances the torques due to the 2 balls.

    2) help coming up

    for this just use simple newton's laws ...
    upward force due to pivot balances the plank and the yellow and green ball's weights.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook