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Homework Help: Centripetal Force Lab Questions?

  1. Dec 15, 2013 #1
    So we did a lab in physics today and it was a contraption where we had a stopper on one get of the string, and weights on the other, and we spun the stopper around, and there's 4 questions that i don't under stand, so if you could help me with this, and please explain as i want to know how to do this, that'd be awesome!


    1. In an experiment using this apparatus the mass and centripetal force are kept constant, by how much must the velocity change to increase the radius a factor of four(4X)?

    2. You calculated the acceleration of the stopper for both lengths. What factors determine the acceleration and rank the factors from greatest to least.

    3. Suppose you find that a centripetal force of 12 Newtons is required to keep a given object in a particular circular path when it is moving with uniform speed. Assume you are able to double the mass, velocity, or radius individually at will.
    a) What will the magnitude of the centripetal force be for each of these individual changes?

    b) Which change modifies the centripetal force the most and why?

    4) Write the equation for centripetal force in terms of: mass, revolutions, radius, and period (using any constants needed).
    a) What effect would an error in time measurement have on the F in time was too large?
    b) What effect on the calculated F would a radius have if the value used for radius was too small?
  2. jcsd
  3. Dec 15, 2013 #2


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    To my mind this is a really poor experiment but it's the one everyone gets told to do. It must be that the equipment is so easy to make. The problem is that the weight of the stopper is constant so you have to vary string length AND rotation rate to fit the same centripetal force. It would be much better if you could have the string of a fixed length and measure the force for a given rotation rate. The way you did it is (imo) more demanding and it gives 'them' a chance to make you think more (God forbid!!!)
    Look at this link. It tells you the relationship between V and r and string tension (centripetal force = stopper mass times acceleration).
    That equation is what you need in order to answer the questions. Re-arranging it to put what you want on one side will tell you how to answer.
    Come back with some thoughts on this as I don't want just to give you the answer.
  4. Dec 15, 2013 #3
    Here's what i got for my answers
    1. 8 times



    3b. The mass, and the velocity, the higher the mass the more higher of velocity you need to maintain the speed

    4. F(of centripetal force) = m4(pi^2)rf^2

    and i'm working on 2 and 3a ... still
    Last edited: Dec 15, 2013
  5. Dec 15, 2013 #4
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