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Difficulty with non-inertial frames

  1. Feb 22, 2008 #1
    I seem to be having some trouble processing non-inertial frame homework problems. I hear that sometimes attempting to explain the problem helps with the understanding so here goes. I don't think I have any difficulty visualizing the problems. Creating free body diagrams (FBD) from the non-inertial (NI) reference frame are pretty easy using fictitious forces. And I know I'm o.k. at FBD's from inertial (I) reference frames. But I seem unable to combine them properly mathematically to obtain a correct final solution. A good example:

    A kid is on a water slide riding high on a horizontal curve raising her head to look past her toes. With the given radius and velocity I have no trouble obtaining centripetal accel. and the radial force. Knowing that her neck muscles exert a given force while at rest (lying down) to lift her head normally I need to determine the force req'd to look past her toes on the slide. My first attempt used the assumption that I needed to determine the mass of her head and multiply that by the centripetal accel. to find the force req'd to lift her head at that velocity against the "centrifugal" force. It seems I didn't need the mass and I should have used only accel. components. And I foolishly assumed gravity wasn't an issue. I also think I forgot about basic vector addition in solving, arrrgh! Finally, the solution used the ratio of accel. of -NI- vs. -I- to determine a multiple for the original force to lift her head to obtain the final answer. I'm not sure I would have thought of that.

    I suppose my main questions are; What suggestions can anyone give as to a good course of action to better solve these types of problems? And, if no suggestions is it better to just continue to plug and chug a lot of these till I get the hang of it.
     
  2. jcsd
  3. Feb 22, 2008 #2
    Welcome to PF.
    YOUR PROBLEM DOES NOT LIE IN NON INERTIAL FRAMES BUT RATHER THE ABILITY TO EXPRESS IT MATHEMATICALLY.ROTATION AND CONCEPTS OF ANGULAR VELOCITY ARE VERY IMPORTANT COURSE AND BEFORE YOU PROCEED TO SOLVE ANY NUMERICALS ALWAYS HAVE THE THEORY WITH YA.

    http://www.mel.nist.gov/div822/basic.htm
     
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