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Can I get some help with my investigation?

  1. Sep 18, 2014 #1
    Fist off, this isn't homework, so...

    I'm doing an investigation, calculating gravity, and I have 2 experiments ready, with everything accounted for. However, I do not know some variables for my other 2 experiments.

    1. Ball on a Slope.

    I am rolling a ball on a slope through 2 light gates, and calculating the final velocity and time it took for the ball to pass through. However, I understand how friction would be a factor, and so I tried to derive an equation that combined gravity with friction, but I couldn't get one that worked.

    Could anybody help?

    2. Secondly, I wanted to use a Kater's Pendulum, but I can't find any experiments that I could do using one online, and I have no idea how it works. I was just told by my teacher that it is the most accurate method.

    Thank you for any help you provide!



    I am doing an SQA Advanced Higher

    I am rolling it down a slope, because it is a part of my required investigation; I need to use it as an integral part (The introduction.) I need to have an investigation that isn't very accurate, as to provide something for my discussion section to reflect on.

    Secondly, I have got a Simple Pendulum and a Compound Pendulum already, and I need a Kater's Pendulum Experiment.
    Last edited: Sep 18, 2014
  2. jcsd
  3. Sep 18, 2014 #2


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    Hi and welcome to PF

    I do not know what your level of Physics is but, assuming it is not too advanced:

    1. Is there a reason for preferring a ball rolling down a slope to a ball simply falling between two light gates? A slope will involve friction but air friction at low speeds can be neglected.
    2. A simple pendulum (mass on steel wire) will give a pretty good value for g if you eliminate draughts and the temperature does not vary the length of the wire. Before you use Kater's method, you should be in a position to understand it; I think your teacher should have avoided telling you about it unless he / she knew you could cope with the Maths and be fully conversant with Moment of Inertia.

    Once you have obtained results by the above simple methods then you could progress further. But, the way college and school projects go, you will probably find that the allocated time would be taken up with the simple versions.
    Last edited: Sep 18, 2014
  4. Sep 18, 2014 #3


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    If the ball falls rather than rolls you also eliminate any issue with the moment of inertia of the ball.
  5. Sep 18, 2014 #4


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    You can account for the moment of inertia of the ball. It's more complicated, but not too much more. There's a frictional force pointing uphill which is just strong enough to enforce the no-slip condition.
  6. Sep 18, 2014 #5


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    Staff: Mentor

    Welcome to the PF. I've moved your thread to the Homework Help forums, where all posts about schoolwork belong. :smile:

    Now, what equations are you using in these experiments to calculate the acceleration of gravity? Finding those equations is part of your project, and we need you to show the effort of finding those equations.
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