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Homework Help: Conceptual question - rotational+translational motion

  1. Nov 18, 2013 #1
    So, we are learning about simultaneous rotational and translational motion. I understand that they can be dealt with independently -- for example, if 2 identical rods have a force applied to them at different points, their rotational motion will differ but they will both have the same center-of-mass acceleration. But I am having a really hard time understanding WHY this is. It seems like if a force was applied to the end of the rod, some of the energy given would go towards spinning the rod, and it would move less (translationally) than if a force was applied at the center of one side of the rod. Can anyone clarify why this is not the case?

    Relatedly I am having trouble understanding how 2 identical objects given the same force can end up with different total kinetic energies, due to one of them having a rotational component of KE. It just doesn't make sense to me intuitively.
  2. jcsd
  3. Nov 18, 2013 #2


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    welcome to pf!

    hi rbigongi! welcome to pf! :smile:

    force x time = change in momentum

    force x distance = work done = change in energy​

    if you apply the same force for the same distance, then yes the energy will be the same

    but we usually talk about applying the same force for the same time :wink:

    (the same impulse)
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