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Static equilibrium and a ladder

  1. Nov 21, 2006 #1
    A ladder leans against a frictionlee wall. If the bottom of the ladder is pushed closer to the wall (so theta increases) which of the following change? Why or why not? Assume the ladder is in static equilibrium.

    a) Normal force exerted by the ground

    b) Normal force exerted by the wall

    c) Friction force exerted by the ground

    The correct answer is that the a will not change but b and c will change.


    This is my reasoning...

    The normal force exerted by the ground will not change. All it does is to balance out the force of gravity. If the ladder falls, it will be rotated about the point at the bottom of the ladder touching the ground. Therefore, it doesn't contribute to torque.

    The normal force exerted by the wall will change if the ladder is pushed closer to the wall. The normal force is trying to resist gravity as well as the clockwise torque. It provides a counter clockwise torque to prevent the ladder from falling. As theta increases, this normal force will decrease.

    The friction force exerted by the ground will be affected. It prevents the ladder from falling. It needs to balance the normal force from the wall in order to prevent the ladder from falling counterclockwise.

    Is my reasoning correct? I think I am missing something, but I am not sure.
     
  2. jcsd
  3. Nov 21, 2006 #2

    PhanthomJay

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    See mark up in red above.
     
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