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The physics of a swinging door

  1. Dec 15, 2009 #1
    the physics of a swinging door !!!

    1. The problem statement, all variables and given/known data
    why is it that its easier to open a swing door by pushing on the open side rather than the hinge side


    2. Relevant equations

    no equations

    3. The attempt at a solution

    a swing door has no latch so thus maybe its to do with force or rotational motion but im not sure please explain
     
  2. jcsd
  3. Dec 15, 2009 #2
    Re: the physics of a swinging door !!!

    Have you studied moments, torques and moment of inertia?
     
  4. Dec 15, 2009 #3
    Re: the physics of a swinging door !!!

    yes i have studied torque.. but still im not sure what the question is really askin.. can u please eloborate or give me some hints atleast
    thnksss
     
  5. Dec 15, 2009 #4
    Re: the physics of a swinging door !!!

    think about inertia and torque especially.
     
  6. Dec 15, 2009 #5

    DaveC426913

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    Re: the physics of a swinging door !!!

    When you tighten a bolt with a wrench, do you hold the wrench near the head, or near the tail?

    When you saw a seesaw, do you sit near the centre, or near the end?

    Which way is easier? Why?
     
  7. Dec 15, 2009 #6
    Re: the physics of a swinging door !!!

    on the seesaw we sit on the edge and that is because equal amount of torque net force acts on each individual. i studied the troque but im not sure what they are askin on my question about the door., it wil help me out if you can answer the question and i will try to understand it
     
  8. Dec 15, 2009 #7

    ideasrule

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    Re: the physics of a swinging door !!!

    OK, here's what the question's asking.

    You push sideways on an open door. It's easier to close the door if you push near the doorknob than if you push near the hinge. Why?

    To answer it, what's Newton's second law for rotational motion?
     
  9. Dec 16, 2009 #8

    DaveC426913

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    Re: the physics of a swinging door !!!

    Right. But what if one of you sat near the centre while the other one stayed at the edge?

    Would this work? Why not?

    What's different in terms of the forces the two sitters can apply?
     
  10. Dec 16, 2009 #9
    Re: the physics of a swinging door !!!

    it easier to push the door and open it if we use the door knob.. because the hinge is the axis upopn which the rotation occurs. using the door knob we can apply force easier and get higher acceleration.. and newtons second law of rotational motion is

    external torque net = moment of inertia * angular acceraltion

    from this i think i can conclude that the moment of inertia for the door is when no one exerts any force on it and angular acceration is how much the door opens.

    I have tried to get answer please help me more please.. i really want to answer this feed back please
     
  11. Dec 16, 2009 #10
    Re: the physics of a swinging door !!!

    There's another equation for torque.
     
  12. Dec 16, 2009 #11
    Re: the physics of a swinging door !!!

    can some one please give me an answer... im in need of an answer, we have all the relevant points ..
     
  13. Dec 16, 2009 #12
    Re: the physics of a swinging door !!!

    Torque = Distance cross Force. Assume your pushing at 90 degrees. So Torque = Distance times Force. Distance is the distance between the axle and where you push. You can see that D increase cause Torque to increase, when Force stays the same.
     
  14. Dec 16, 2009 #13
    Re: the physics of a swinging door !!!

    I guess they no longer teach

    "give me a lever long enough and I can move the earth.." Archimedes
     
  15. Dec 17, 2009 #14
    Re: the physics of a swinging door !!!

    instead of posting stupid quaotes on this ..y didnt some one put an answer..
     
  16. Dec 17, 2009 #15

    DaveC426913

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    Re: the physics of a swinging door !!!

    Because you're the one who's in school, smartass. :grumpy:

    When you're out there building a drawbridge for your wife and babies to drive over, are you going to stop the next guy on the street and ask him to show you how to build a bridge?

    Maybe crack open your textbook?
     
  17. Dec 17, 2009 #16
    Re: the physics of a swinging door !!!


    That wasn't meant as a put down. I am an instructor who is in the trenches every day busting my butt to teach to teach med school level physiology to a group of students who were sold down the river many years ago. I recall in the second grade being taught about the seven simple machines and recall this quote from the sixth grade.

    I actually use a door as an example in teaching basic physics where I pick out the biggest bruiser in the class but who is restricted to pushing against me on one side of the door at 1/3 the width while I gain the utmost mechanical advantage on the opposite side--so far I have been lucky but no one yet has had three times my eroding strength. :smile:

    Sorry if my remarks were misinterpreted... It wasn't meant as personal in any way, shape or form--just bemoaning the current lack of scientific literacy in the US. If you had the fairly ordinary education I had and most of my generation, you most likely would have known the answer w/o even thinking.
     
  18. Dec 17, 2009 #17

    DaveC426913

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    Re: the physics of a swinging door !!!

    I don't think it was interpreted as a put down at all. I think Idrees is just mad that we don't ... how did he put it? ... "just give him the answer".
     
  19. Dec 17, 2009 #18
    Re: the physics of a swinging door !!!

    Physics can be frustrating. I think the OP was given both broad hints and exact solutions several times, and actually assumed the thread was flayed horsemeat twice diced. Yet I here his frustration as I see it everyday.
     
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