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

A little help pls

  1. Dec 21, 2004 #1
    pls help me with this one..

    most doors are fastened to the wall using two hinges, which are placed symmetrically along the length. why do the screws of the upper hinge get
    ripped off first? :confused:
  2. jcsd
  3. Dec 21, 2004 #2
    I think the weight of the door gives rise to a clockwise moment about the lower hinge. The upper hinge therefore must apply some force to keep the door in place. Due to this if the the door is too heavy the screws of the upper hinge get ripped off.
    Last edited: Dec 21, 2004
  4. Dec 21, 2004 #3


    User Avatar
    Gold Member

    Looked at another way:

    Have you ever seen a door hung with *only* the top hinge attached? I do this when installing a door - attach the top hinge first. What does the bottom hinge do? Well, the bottom half of the door "dangles". You can easily move the door and, with just a little effort, actually put it in place, without even attaching the lower hinge.

    Try hanging a door bottom hinge first. You will likely find yourself on the ground with a bump on your noggin and a door with a ripped lower hinge on top of you.

    Point is, it becomes very evident that there is a *much* larger force acting on the top hinge than on the bottom hinge. The door wants to fall over, and in doing so, it will pivot about a point (the bottom corner of the door) which is very near the lower hinge.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook