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Doubling a load.

  1. Sep 13, 2013 #1
    I came across a diagram of a release mechanism, which shows the operator how to double a release load. I have taking a basic physics course (not advanced) and I can't seem to make any sense of this. I am just trying to understand this diagram; is it correct? Sorry for the drawing; hopeful that it is understandable.

    The diagram states that the release load of a single unit can be doubled by rigging the release as shown in the diagram.

    My Thinking: It seems that the static load will be shared by the chain and the release unit. This does not mean that the release load of the release unit will be doubled. The release load is set by the capacity that the release unit can handle (release mechanism motor). The load is attached to the link in the middle of the chain. The top has three shackles that is attached to a stationary object.

    I cannot seem to wrap my head around this; can someone please give me some (physics) knowledge on how this can work or doesnt work?
    This seems like basic knowledge, so would like to have a refresher course with details on how this works or doesnt work.

    Thanks in advance.

    Attached Files:

  2. jcsd
  3. Sep 13, 2013 #2


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    Science Advisor

    Consider the chain as a single loop that is free to flow through the shackle at the bottom end.
    Since the tension in the chain supports the load, and the chain is a loop, each side of the loop is carrying half the total load. The release mechanism is in one side of the chain only, so it will release at half the total load. After release the free end of the chain must pass through the shackle to complete the release.
  4. Sep 16, 2013 #3
    I started with the similar thinking when it came down to releasing the load. The only difference is in thinking was that once the load started releasing then this would put all the load on the release mechanism side. I understand the load sharing due to the tension on the chain side; but then once the load begins to release, i figured that the loop in the middle of the chain (holding the load) would slide (lean) towards the release mechanism therefore putting all the load on the release side.

    Can you tell me where I might find an explanation of this in a physics textbook? What concept/lesson would be a great explanation for this?

    Thanks for you input.
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