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Homework Help: Soup Can Race

  1. Jan 20, 2005 #1
    In physics class, we had a soup can race to see which can of soup would get to the bottom of the ramp first.....

    the length or height of the ramp was given but there were 2 kinds of soup used

    one was french canadian pea soup and one was chicken broth

    the chicken broth got to the bottom first by quite a bit for such a short ramp

    now, i have to explain why this happened

    i am currently debating the viscosity of the fluids and that sort of thing and looking at what else may have an influence

    does anyone else have any other ideas?
  2. jcsd
  3. Jan 20, 2005 #2
    What about the moment of inertia and rolling?
  4. Jan 20, 2005 #3
    i was thinking about that but then came up with since the friction is proportional to the normal force, and normal force is proportional to gravity, and gravitational force is proportional to mass, mass therefore affects friction and the more total energy it takes away from the input force

    i had to think in terms of conservation of energy :grumpy:
  5. Jan 20, 2005 #4


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    I think you're on the right track with the viscosity of the fluids.

    futbol touched on the key to the problem - the one with the greatest moment of inertia accelerates slower.

    The problem with caclulating the moment of inertia of soup is that it always moves inside the can while the can is rolling.

    Of the two, calculating the moment of inertia of chicken broth would be the easiest, since you can pretty well count on all of it winding up at the lowest spot inside the can. On the other hand, French Canadian pea soup is particularly hard to calculate a moment of inertia for. You don't know how much has fallen to the lowest spot in the can and how much is still sticking to the high side of the can.
  6. Jan 20, 2005 #5


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    Wouldn't both cans be full? I would agree the viscosity would be a factor, but am not sure there's going to be any difference in the amount of soup at the top or bottom of the can, but instead how easily it rotates around inside. Though, on the other hand, chicken soup would have more solids that I would expect to keep settling toward the bottom, while pea soup might remain more uniform. Hopefully you don't actually have to calculate actual values for the two soups and can just answer in words. I like this demo though...sounds fun to have soup can races!
  7. Jan 20, 2005 #6
    Would be fun to have it at my school. :rofl:
  8. Jan 20, 2005 #7


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    Shake 'em and see. I know Clark's chicken broth isn't quite filled to the rim (you can hear it shake inside). Campbell's vegetable soup shakes, but much less than Clark's chicken broth. Cream of celery and cream of mushroom don't shake inside at all, that I can tell.

    Tomato juice definitely is not filled to the very top. I've done tomato can races with a frozen can of tomato juice and a normal can of tomato juice and you get the same drastic difference that marko_tomas_13 got. Except when both cans have the same thing inside, the reason for the difference is a little more obvious. (By the way, make sure the tomato juice can is standing upright when you freeze it. I saw someone try to do this demo with a can of tomato juice that had been laid in the freezer on its side - it's pretty humorous for the class (the can won't roll, it just slides down the table), but it's kind of embarrassing for the person doing the demo.
  9. Jan 20, 2005 #8


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    I guess they can't fill them all the way when people are running around freezing the cans! :biggrin: Sounds really cool. I actually like the idea of adding the can frozen on its side to the demo! It would be helpful then to have a can opener ready to show the different pattern the soup was frozen inside between the two. Why didn't I have cool demos like this in school?!
  10. Jan 21, 2005 #9
    Yeah, that would be cool!! :rofl:
  11. Jan 21, 2005 #10
    shaken, not stirred lol

    i actually did shake them....and we agreed that each can of soup had the same volume (according to the label) but also that they had the same ammount of soup inside

    when the broth was shaken it could easily be heard...when the pea soup was shaken, i could still feel it moving around, but it could not be heard like the broth because it is more viscous

    that plays a big role

    and in fact we dont have to calculate, we just have to explain in words in terms of conservation of energy....Et1 = Et2
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