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Pushing and pulling forces

  1. Dec 1, 2003 #1
    Hi I am new to physics so be gentle!

    I am involved in training people in lifting, carrying, pushing and pulling.

    My question is: If I wanted to measure the pushing force required to move a trolley/cage/bin on wheels could I use a pair of weighing scales mounted on the trolley/cage/bin to measure the force?

    2nd question: If I know the weight of the trolley/cage and its load weight is it posible to do a basic calculation of the pushing force required to start to move the trolley and the force to keep it moving. Or would I always have to measure it presisely?

    many thanks for your replies.

    Peter
     
  2. jcsd
  3. Dec 1, 2003 #2

    chroot

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    Welcome! Glad to have you here. :smile:
    In principle, yes, you can glue bathroom scales to the trolley and use them to measure the force necessary to get the train moving. All an "ideal" bathroom scale does is display the force applied to its top surface -- in other words, the force "squeezing" its top and bottom surfaces together. In practice, however, bathroom scales may not work mounted horizontally, or they may be wildly inaccurate. Besides, I think bathroom scales only go to a few hundred pounds. A more precise measuring tool is a spring scale -- you attach one end to the trolley, and pull on the free end of the spring. The amount the spring stretches is a measure of the force applied to it. Of course, I'm not sure where you would get such a spring..... maybe someone else has some practical engineering expertise. Strain gauges maybe?
    If the trolley were just a block of wood sliding on a surface, you could easily calculate the force required, considering the coefficient of friction between the wood and the surface.

    However, the trolley is quite a bit more complicated. The friction experienced by the trolley is due to the bearings of its axles and the deformation of the wheels and track as it rolls. These are very complex mechanisms, and probably, well, virtually impossible to calculate with any success.

    - Warren
     
  4. Dec 1, 2003 #3

    jcsd

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    Yes it'd proably be alot easier to use a newtonmeter as they are designed to measure just these sort of things. I've got no idea where to get one of these from, but I don't imagine they're too difficult to get hold of.
     
  5. Dec 1, 2003 #4

    chroot

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    ...but make sure you express your trolley in joules.

    - Warren
     
  6. Dec 1, 2003 #5

    jcsd

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    Another thing about newtonmeters, make sure you get one that can measure the sorts of forces that are involved as they come in all sorts of different ranges.
     
  7. Dec 1, 2003 #6

    jcsd

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    Last edited: Dec 1, 2003
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