Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Contraption to apply constant force

  1. Nov 9, 2013 #1
    What is a contraption I can make at home somewhat easily to apply a constant force to a block? I am doing an experiment on how far the block will slide. I was thinking about making some sort of pendulum but would love to hear some of yours guys ideas.

    Thanks
     
  2. jcsd
  3. Nov 9, 2013 #2

    UltrafastPED

    User Avatar
    Science Advisor
    Gold Member

    Springs are good ...

    Or you can get a pulley, a wire, and a bag of sand; you may have to build a platform.
     
  4. Nov 9, 2013 #3
    Would a spring work better than a pendulum?
     
  5. Nov 9, 2013 #4

    UltrafastPED

    User Avatar
    Science Advisor
    Gold Member

    I don't see how you plan to use a pendulum as a force ... or do you plan to just use the bob? In that case it's like the bag of sand ...

    For a spring the force is proportional to the extension/compression.
     
  6. Nov 9, 2013 #5
    I was planning on putting something on the end of the pendulum and raising it to a certain point every time and letting it hit the block at the bottom.
     
  7. Nov 9, 2013 #6

    UltrafastPED

    User Avatar
    Science Advisor
    Gold Member

  8. Nov 9, 2013 #7

    K^2

    User Avatar
    Science Advisor

    Not in general. The force that would actually be transfered to the block is tension in the string. While tension in the string is equal to m(g-a) of the weight. If acceleration of the block and the suspended weight are constant, then yes, the force applied will be constant. If for whatever reason, acceleration is not uniform, than neither will be the applied force.

    If you want to look at it another way, no matter how much weight you suspend, you'll never have the block accelerate past g.

    In all fairness, this is probably good enough for whatever OP is doing. But he should consider his exact experimental conditions and how precise things need to be.

    In engineering applications, when it is necessary to provide a large, constant force to a moving object, hydraulics are used. For example, arresting gear on aircraft carriers will typically use a hydraulic system. It is relatively easy to set the relieve valve to desired pressure, and that means the piston will not apply a force in excess of that set.

    Of course, here, you also have to take into account mass times acceleration of the piston itself. But it is usually negligible compared to the force applied.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: Contraption to apply constant force
  1. Force applying (Replies: 5)

Loading...