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Device with transfer of KE-PE each cycle & losses

  1. Jun 9, 2014 #1
    I have a project which is to create a mechanical device that would transfer close to 1 J of energy from one form to another and must be able to show how you calculated the 2 energy individualy and show that the enegy loss between the 2 is within a % difference.

    I posted on here yesterday asking help on calculated the Ep and Ek of a pendulum (which was my initial device idea). Now finding Ep of a pendulum was easy, the real problem came at finding the value of Ek after loss of energy due to air resistance. In order to find Ek we would have to find velocity. since we couldn't just go Ek=Ek and figure out the velocity that
    way because we have to take air resistance and loss of energy due in to consideration, there was really no other way of going about finding velocity at the bottom without some really scientific device. So that idea ended up being a fail.

    Now this project is suppose to be due tomorrow and I have yet to thought of another device that could transfer energy for one form to another and be able to calculate each energy individualy.

    If you guys van give me any suggestions for a simple device, I would be much appreciated. Thanks for the help!
  2. jcsd
  3. Jun 9, 2014 #2


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    Staff: Mentor

    Since this is your schoolwork assignment, we cannot do the work for you. At best, we can offer hints and ask questions that may help you to figure out a suitable mechanism and do the calculations.

    Since friction seems like the most likely way to introduce losses, what oscillatory mechanisms can you think of that have some frictional losses?
  4. Jun 9, 2014 #3
    I have thought of doing a spring of a mass on it and its just bouncing up and down. So that would be from Elastic potential to Kinetic energy. But again the problem comes with finding the velocity right at the middle. Since we have to take that energy will be lost to consideration it will be extremely hard or even impossible to find the velocity and calculate Ek with that velocity.
  5. Jun 9, 2014 #4


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    Staff: Mentor

    I would have chosen a similar mechanism, but I tend to think sideways rather than up and down.

    BTW, how far are you in calculus right now? Have you had some differential equations?
  6. Jun 9, 2014 #5

    I am in grade 10 so I have only pass grade 10 Math.

    I really liked the idea of the pendulum, and the Ep to Ek transformation. But there is really no accurate way of finding out the velocity to calculate Ek.
  7. Jun 9, 2014 #6


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    Staff: Mentor

    Well, without using calculus, you will need to make some simplifying assumptions, IMO.

    One is to avoid using air resistance as the loss mechanism. It is velocity-dependent, which complicates the equations. Using rubbing friction instead should help to simplify things.

    So I'd recommend using a horizontal setup of the spring and mass, on a low-friction surface. If the losses are small for each cycle, you can make some simplifying assumptions about the effect of the losses on the motion of the mass.

    Can you write the equations for when there is no friction? Then what are your ideas for how the equations will change with a very small amount of friction?
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