Downward force, please help

  1. I am making a soil container of size 1meter x 1 meter x 0.60 meter or (3.2feet x 3.2 feet x 1.9 feet)
    with soils in it, it weights approx 2000 pounds/900 kg.

    I want to know, how can i reduce the downward force of that 900kg.
    (the bottom of the container can be slide open, hence i need a lower downward force, so that its lighter to slide)

    I found a way to do that by putting a beam on the middle of the container, is there a more effective way?

    Thank you geniuses
     
  2. jcsd
  3. Simon Bridge

    Simon Bridge 15,043
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    Welcome to PF;
    You can't.

    The force is due to gravity acting on the mass - so you could reduce the soil volume.

    What you want it to make it easier for the bottom to slide open.
    Assuming contact with the ground is not the problem, but soil pressing from above, you need to reduce the pressure of the soil.

    You can do that by:
    1. tilting the container so the bottom is no longer horizontal;
    2. placing something between the sliding thing and the soil (to reduce the friction);
    3. change the sliding whatever with a hinged one - then the weight will help it open;
    4. make the slider smaller.
     
  4. you can increase the bottom surface area of container, so the pressure on bottom decrease.
    to maintain the constant amount of soil, you can decrease the height of container.
     
  5. Thank you for the detailed reply. Is there any way that the pressure will reduce by changing the shape?
     
  6. I have no idea what "putting a beam on the middle of the container" means.
    1. A horizontal plate, moving under soil, experiences frictional forces. As Simon says, reducing the coefficient of friction, by lubrication, or say, using a plactic sheet will reduce the force necessary to move the plate. Teflon is expensive but will do the best job here.
    2. You would reduce the force if you put a grate above the plate to help support the dirt. Depending on how cohesive the soil is, this may work...but then again will prevent at least some of the soil from falling.
    3. Its not clear to me why you failed to describe your set up. How is the bottom plate/floor/panel supported???
    Lets say it is only supported by the groove it slides into on the side-walls. There are two possible sources for additional forces: one is our old friend friction - lubricants, and ball (or roller) bearings would reduce that as above. The other possibility is that the weight of the soil is deforming the plate so that it is in contact with the groove (binding). Increasing its rigidity (thickness or supporting 'rafters') would reduce deflection which might be binding it in its groove.
     
  7. Simon Bridge

    Simon Bridge 15,043
    Science Advisor
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    But: reduce pressure by increasing the area of the bottom for the same mass - this means shallower soil.

    But I suspect your problem is more related to friction.
    The door slides along a track of some sort (whatever it is that stops the door just falling out) with soil pressing on the other side?

    You can lubricate the track
    You can put bearings on the track
    You can include a lever or other simple machine to multiply your effort.

    A smaller door in the bottom - maybe two half-size doors instead of one big one.
    Use a completely different design of door - hinge or iris perhaps.

    You can construct a sloping bottom (say, like an inverted pyramid or prism) - put the sliding door in the sloping sides.

    You are basically spoiled for choice here - what is the context for this project?
     
    Last edited: Apr 19, 2014
  8. My idea is not good as of Simon Bridge's idea.
     
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