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Forces on a hanging string

  1. Sep 6, 2013 #1
    I thought about this when hanging my belt on to the towel holder. If i put too much of the belt on one side, that side would fall down. Why does this happen? Shouldn't the towel hanger just put up an equal force to the total weight of the belt keeping it up?

    I understand a little when we say that the towel hanger acts as a pulley so the direction of the force can be changed but i still don't get why an upwards force isn't present to hold the belt up actually.

    Thanks for the help :)
     
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  3. Sep 6, 2013 #2

    SteamKing

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    It's not that the hanger isn't exerting enough force on the belt to hold it up. A physicist would rely on his powers of observation to formulate a theory.

    Ask yourself, why does the belt fall if the amount of weight isn't balanced between the two sides? What happens where the belt is resting on the holder? Is there anything on the holder which can resist the motion of the belt if, for whatever reason, the belt starts moving? Can the belt be placed on the holder in another way such that it will not slip off?
     
  4. Sep 6, 2013 #3
    Hi thanks for the reply :)

    Using the tension and forces we learned, it would be because one side of the rope has more weight than the other so it would have a net downwards force while the other side would have a tension that would pull the lesser weight up. But while these 2 processes occur, does the holder exert an upwards force too?

    Thanks for the help
     
  5. Sep 7, 2013 #4

    SteamKing

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    Indubitably. Draw a free body diagram of the belt and the holder.

    Look, your holder is not magic. The belt and the holder both probably have slick surfaces. The belt falls off the holder, if it is not evenly hung, because the unbalanced weight causes the belt to slide.
     
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