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Moment of Inertia-Soup Cans

  1. Feb 13, 2006 #1
    This is probably a very very lame question, as it's probably a very basic concept, but I have been quite ill and missed wednesday through monday's physics lessons. Basically, if I have 2 soup cans- one empty, one with soup in it, and set them on an inclined plane, which will hit the bottom first?

    My initial interpretation of moment of inertia seems to be that I'm looking for the object that will most resist motion. If it were a solid base inside a can going against a liquid soup can, then I'd say the liquid one would win, as it would not have to roll it's mass along with the can, as a solid base would. However, in this case, though I don't have a way to explain why, my guess would still be in favor of the liquid-filled can, perhaps because the mass is more centered in its case? Sorry, my head is really fogged up here. I'd love to hear that this theory is correct, but if not I'd also love to hear an explanation that I can make sense of. Thanks!
  2. jcsd
  3. Feb 13, 2006 #2
    To help you out, take the solid disk and hollow ring example. A hollow ring's general moment of inertia equation is [tex]I=mr^2[/tex] and the disk's equation is [tex]I=\frac{1}{2}mr^2[/tex]. By looking at these equations, you can tell which one has the greater moment of inertia. Think about why a hollow ring has more moment of inertia than does a solid ring (also called a disk). Think about the location of the object's mass from its center.
    Last edited: Feb 13, 2006
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