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Force Required

  1. Sep 22, 2011 #1
    What would be the approximate force required on the perimeter of a 30 ft diameter table that weighs 200,000 lbs to move it? The table is sitting on twelve wheels (10" diameter each) that are mounted to ball bearings.
     
  2. jcsd
  3. Sep 22, 2011 #2
    A quick approximation would be:

    Force = coefficient of static friction X weight.

    The rubber-to-road friction is likely larger than the bearing friction (assuming the bearings are in good condition).

    My old physics textbook lists for coefficient of static friction = 1 for rubber on dry concrete.

    Edit:

    The method above will significantly over-estimate the force since this would only apply if the tires could not roll.

    I will look into this a little more...
     
    Last edited: Sep 22, 2011
  4. Sep 23, 2011 #3
    The rolling resistance coefficient (RRC) for rubber automobile tires is about 0.01 (less if the tires are inflated more). Thus for a car weighing 3000 pounds, the horizontal force needed to push the car (overcome the RRC) is about 30 pounds.

    For your case, I would guess about 0.01 x 200,000 pounds = 2,000 pounds tangential force on the perimeter of the table.

    Bob S
     
  5. Sep 24, 2011 #4

    AlephZero

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    I don't think you are going to support 200,000 lbs on 12 10-inch-diameter rubber tires. The weight on each tire would be about 7.5 tons. Compare "one 10-inch diameter wheel" with the wheels and tires on a typical 7-ton road truck!

    The question is impossible to answer unless we know more about the wheels, and what surface they are running on. You would probably need a specially built track to support that weight with such a small contact area. Otherwise, the most of the force will be overcoming the deformation of the ground and/or the wheels, not overcoming rolling resistance or friction in the bearings.
     
  6. Sep 24, 2011 #5
    Where the heck do you have a 100 ton table and why would such a table have wheels?
     
  7. Sep 25, 2011 #6

    AlephZero

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    There are plenty of mobile engineering structures that weigh more than 100 tons. That is only the weight of three large "standard" road trucks. But supporting them on twelve 10-inch diameter wheels is not so common.
     
  8. Sep 25, 2011 #7
    I don't mean to get off track here, but I hotly disagree that there are plenty of 100 ton TABLES that are required to be mobile, 10 inch wheels or not.
     
  9. Sep 27, 2011 #8
    The gross weight limit of a standard US rail freight car is about 286,000 pounds, supported on eight 33" diameter steel wheels (35,750 pounds each). The rolling resistance coefficient of steel wheels on a steel rail (without deformation) is about 0.1%.
     
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