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Homework Help: Physics Lab on Cans & Liquids

  1. Sep 10, 2008 #1
    1. The problem statement, all variables and given/known data
    You are given two cans to roll down a 1m ramp at angle 15 degrees [and then at 30 degrees for a check].
    Can A has a less viscous fluid, broth.
    Can B has a more viscous fluid, cream of mushroom soup.

    Now through constant experimentation we find that, can B rolls down the ramp and ends up further than A, even though A accelerates much faster than B down the ramp.
    And, what is the pathway of energy [where energy goes from X to 0, where X is the initial energy of both cans at the top of the ramp]

    2. Relevant equations
    GPE : mgh
    Linear KE: 0.5mv^2
    Angular KE: 0.5Iw^2
    [Whatever else applies]

    3. The attempt at a solution
    For the why, a theory is devised:
    Neglecting friction, and gravitational force due to the can's having the same mass, and the liquid's mass having a difference of less than 1%, we look into just the Kinetic energies.

    We can choose two extremes to represent the viscosity: water[A] and honey.
    Therefore, since this is a blackbody problem we can only assume, that the liquid in A remains at the bottom and thus linear. However, the liquid in B is more viscous, therefore it rolls with the can to a certain extent, or at least more than the low visous water.

    This means, by the end of the ramp, we can assume that A has more linear kinetic energy, while B has more angular kinetic energy, for the reasons above.

    And through various trials, it was seen that linear kinetic energy is easier to diminish than angular kinetic energy. Therefore, Can B rolls further than Can A, even though Can A moves faster down the ramp.

    This is a theory, and we [my lab group and I] could use some feedback/comments/questions/concerns/la di da.

    As for the energy pathway.
    We don't want to draw the entire thing here, but just raise some points.
    Firstly, the energies we see affecting the cans are:
    Potential Energy [Gravitational], Kinetic Energy, Energy Loss due to Friction, Energy Loss due to Drag.
    Is there any other energy we are missing?

    Any ideas how we can show, via data, how these are lost/spent/gained throughout the lab?

    Thank you for your help =).
  2. jcsd
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