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A top with liquid inside

  • 04-01-2014 12:16pm
    #1
    neufneufneuf
    Registered Users, Registered Users 2 Posts: 321 ✭✭


    A top with water inside turn. It's on Earth under gravity. A part of top has an object with density near 0. I thought it's necessary to put the main axis at the center of mass but like the top is a gyroscope the force move the gyroscope in another plan.

    First image:

    1/ the force F can works ?
    2/ if the force works, this change the angular speed of the top ?

    Second image:

    It seems the sum of centripetal forces are not 0, Fc1 and Fc2 compensate around themselves, but what compensate Fc3 ? If Fc1 compensate exactly Fc2 and Fc3, if there is no gravity, the Fc3 don't pass through the center of mass, so the top turn alone ?


Comments

  • #2
    dlouth15
    Registered Users, Registered Users 2 Posts: 1,169 ✭✭✭dlouth15


    neufneufneuf wrote: »
    A top with water inside turn. It's on Earth under gravity. A part of top has an object with density near 0. I thought it's necessary to put the main axis at the center of mass but like the top is a gyroscope the force move the gyroscope in another plan.

    First image:

    1/ the force F can works ?
    2/ if the force works, this change the angular speed of the top ?
    Is F pointing towards the axis of the top?


  • #3
    neufneufneuf
    Registered Users, Registered Users 2 Posts: 321 ✭✭neufneufneuf


    For F yes. I don't draw forces that pointing to the center of the circle, because it's an axis, the force is canceled by the center I think ?

    For the second case, I simplify the study with only solid. I turn at x rpm 2 masses M situated at d from axis of rotation, these masses can only turn around one axis. This need energy E1. I give freedom of axis, the torque from centrifugal forces give additionnal rotation, the system have more energy ?


  • #4
    dlouth15
    Registered Users, Registered Users 2 Posts: 1,169 ✭✭✭dlouth15


    neufneufneuf wrote: »
    For F yes. I don't draw forces that pointing to the center of the circle, because it's an axis, the force is canceled by the center I think ?
    If you have a force pointing at the pivot would you expect that force to have an effect on the angular momentum?


  • #5
    neufneufneuf
    Registered Users, Registered Users 2 Posts: 321 ✭✭neufneufneuf


    Yes, it's not possible ?


  • #6
    neufneufneuf
    Registered Users, Registered Users 2 Posts: 321 ✭✭neufneufneuf


    In fact, it's easier to understand with 2 masses only, no liquid, no gravity, no friction, only one case. Look at image, the masses create a torque, this rotate the system and add additionnal velocity ?


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