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Need help with homework

  1. Dec 13, 2006 #1
    Okay here is my question.:shy:

    If Total Energy should be constant, because the loss in Potention energy should equal a gain in Kinetic Energy, where does the missing total energy go to ?

    Here is my data;
    TOTAL ENERGY: MISSING ENERGY:
    .1254 .00132
    .1236 .00103
    .1239 .00106
    .11883 .0062
    .1241 .00085
    .1049 .02007
    .12254 .00246
    .1189 .00608
    .1153 .00961
    .1191 .00586
    .10509 .0191

    To obtain my missing energy I took the highess total energy which is the top of the pattern, .1254 MINUS the other results to obtain my missing energy.

    DESCRIPTION: In our lab we used a ball and let it accelerate down a slope that starts high, goes DOWN and back UP with a smaller height and goes back down.

    MY question is: If Total Energy should be constant, because the loss in Potention energy should equal a gain in Kinetic Energy, where does the missing total energy go to ?

    HERE is some hints that our teacher gave us to get through the question

    A) Where is the ball missing the least amount of energy? Why ?

    B) How else is the ball using energy ?

    C) If friction only creates heat in kinetic mode does friction created heat account for the missing energy ?

    D) Is the ball missing more and more energy from one end of the track to the other how can it get energy back once its gone ?

    Really hope you can help, if you need further data just let me know I can provide some more including the height from which we drop the ball from, the balls mass, speed and time through photogates from the stop.

    Thank you. :approve:
     
  2. jcsd
  3. Dec 13, 2006 #2

    berkeman

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    Staff: Mentor

    Hint #1 -- How would the results be different if this experiment were done on the moon?

    Hint #2 -- How would the results be different for a steel ball on a steel track, versus a soft rubber ball on a steel track?
     
  4. Dec 13, 2006 #3
    Well in the moon wouldn't the speed be constant no matter what ?

    And a steel ball... dosen't it depend on its mass... I mean shouldn't it have more PE to convert to KE then the rubber ball???

    AM I right or does this make total nonsense lol ?
     
  5. Dec 13, 2006 #4

    berkeman

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    Why do you say that? You are correct in one sense, but maybe not in all cases.

    I wasn't referring to the difference in mass directly. What else is different about how a rubber ball rolls as opposed to a steel ball?
     
  6. Dec 13, 2006 #5
    Different friction between 2 objets maybe ? IDK lol :S! :cry:
     
  7. Dec 13, 2006 #6

    berkeman

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    Last hint -- What makes the sound as a ball rolls down the track? And do the rubber ball and steel ball make different sounds?

    There are at least 3 effects that I've hinted at. Think more about the hints, and see if you can come up with all 3.
     
  8. Dec 13, 2006 #7
    OK, :confused:

    Don't give up on me, here's my try.

    1) I think on the moon, if there was no force applied on the ball, it would move slower because the gravity is lower than earth ?

    2) A steel ball has greater acceleration than the rubber because they have different friction.

    3) REALLY I can't think of anything about the sounds because its my 1st year at an english school and I'm french and I really am struggling in physics so my guess is that a steel ball has more potentional energy because of its width.

    Yeah its all nonsense, I have to get back to my english homework, hopefully you can give me an easier hint. :yuck:
     
  9. Dec 13, 2006 #8

    berkeman

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    1) No, that's not what I'm talking about. What else is different about the moon, other than the 1/6 gravity?

    2) No, assume that they both have enough friction on the ramp so that they do not slip. What is the main difference between steel and rubber (other than mass density)?

    3) What is sound?
     
  10. Dec 13, 2006 #9
    I really don't know, we haven't worked with sound yet... I'd say steel surface is different than rubber... :S
     
  11. Dec 13, 2006 #10

    berkeman

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  12. Dec 14, 2006 #11
    Wait, sound dosen't produce by itself... it must have something to make it happend... wouldn't that something be kinetic energy ? WHICH would explain why there is missing energy ! IS that it!!?
     
  13. Dec 14, 2006 #12

    berkeman

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    That's part of it. Now what about 2) and 1) in my hints in Post #8?
     
  14. Dec 14, 2006 #13
    1) No, that's not what I'm talking about. What else is different about the moon, other than the 1/6 gravity?
    Its lighter
    2) No, assume that they both have enough friction on the ramp so that they do not slip. What is the main difference between steel and rubber (other than mass density)?
    Steel is harder and rubber is softer
    3) What is sound?
    Already got this one!
     
    Last edited: Dec 14, 2006
  15. Dec 14, 2006 #14

    berkeman

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    1) No. Let's try this another way. What if you did the rolling ball experiment under water?

    2) Yes! So what happens to the shape of the softer ball when it rolls? What does that mean in terms of how much energy gets converted into ______?
     
  16. Dec 14, 2006 #15
    1)Well depending on steel's density, it would either find itself at the botom of water or float to the top without even following the pattern

    2)Friction ?
     
  17. Dec 14, 2006 #16

    berkeman

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    1) No! :grumpy: Assume the dang steel ball is denser than water. When you do the experiment under water, does the steel ball accelerate faster or slower than in air (or on the moon)? Why?

    2) No. Modified hint -- which rolls more easily: a car tire that is properly inflated, or an underinflated tire? Why? What is important about the "more easily" part?
     
  18. Dec 14, 2006 #17
    1) Slower, because the water makes it hard to accelerate which I don't know how to explain

    2) The car tire that is properly inflated because... AIR!
     
    Last edited: Dec 14, 2006
  19. Dec 14, 2006 #18

    berkeman

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    1) Why does a dog's face look funny when it sticks its head out the window of a moving car. And don't just say "air" What ABOUT air?!
     
    Last edited: Dec 15, 2006
  20. Dec 15, 2006 #19

    andrevdh

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    Homework Helper

    Could you provide us with a little bit more information about the experiment please?

    1. Do the track form one continous curve from one side to the other (maybe something like a section of a circle)?

    2. Did you release the ball at different heights on the same curved track?

    3. Did you release the ball out of rest?

    4. Is the total energy of the ball its potential energy at point of release?

    5. How did you determine the missing energy?
     
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