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Homework Help: Law of Conservation of Energy of a wind turbine

  1. Oct 9, 2015 #1
    1. The problem statement, all variables and given/known data
    "identify the type of energy conversions present in each of the following situations. Some questions may use multiple types of energy."

    1) a wind turbine producing electricity
    2) two children sliding down a hill on a toboggan
    3) a toaster oven browning a bagel

    2. Relevant equations
    There are no equations for this, just definitions for different types of energy!

    -
    elastic potential energy - kinetic energy - electrical energy
    - chemical potential energy - sound energy - radiant energy
    - nuclear potential energy - thermal energy - gravitational potential energy

    3. The attempt at a solution
    These are what I think the answers may be:

    1) Kinetic to electrical energy
    2) kinetic energy to thermal energy
    3) electrical energy to thermal energy

    Im not entirely sure if these answers are correct. It would be much appreciated if someone could help me identify the other types of energy I may be missing in my answers.
     
  2. jcsd
  3. Oct 9, 2015 #2
    Don't take my word for these, but consider that in a real life situation for 1, there would be friction in the moving turbine, and in situation 2 the energy that is moving them down the slope is coming from somewhere.

    I don't answer often, so hopefully I've not given too little or too much information in this response, and hopefully it helps. Cheers!
     
  4. Oct 9, 2015 #3

    andrewkirk

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    In the toboggan case, there's another conversion prior to the one you describe. Where does the toboggan's kinetic energy come from?

    Ah, I see teetar already mentioned this.
     
  5. Oct 9, 2015 #4
    Thanks for the responses, this is what I've came up with after the fact:

    1) kinetic energy to electrical and thermal


    2) gravitational potential energy to kinetic and thermal energy


    3) electrical energy to radiant and thermal energy (Possibly chemical energy as well as the chemical composition of the bagel changes while it is being browned)
     
  6. Jan 22, 2018 #5
    Sorry to resurrect this thread, but I have some problems with this question too. Is what ElegantSir is saying correct because I have come up with

    1. kinetic energy of air to kinetic energy of turbine to electrical energy.

    2. gravitational potential energy to kinetic energy

    3. electrical energy to thermal energy (or is it chemical energy?)

    If someone could help me out on these that would be great!!! Thanks.
     
  7. Jan 22, 2018 #6

    haruspex

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    For 1 and 2, as noted in earlier posts, there are losses, so they should be mentioned.
    3 is a bit tricky. Yes, thermal energy. If any chemical energy is produced then, in principle, that could be harnessed. What are the resulting chemicals? Could energy be recovered from them?
    Also, think about what happens to the moisture content.
     
  8. Jan 22, 2018 #7
    Ok so:

    1. kinetic energy of air to kinetic energy of turbine to electrical energy and thermal energy.

    2. gravitational potential energy to kinetic energy and thermal energy.

    3. electrical energy to thermal energy and chemical energy.

    From looking at the above posts, thermal energy seems to be the one that was missing from the first two. I want to understand why this is, is it because everything is composed of/ has particles moving around in it and therefore everything has thermal energy?
     
  9. Jan 22, 2018 #8

    haruspex

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    You have not addressed my objections to listing chemical energy, nor considered moisture changes.
    Thermal energy can be listed because no conversion is 100% efficient. There is is always some friction, or resistance in electrical cables, etc., though whether the question expects you to worry about that I am not sure.
     
  10. Jan 22, 2018 #9
    Radiant energy should be added as that is how the toast ends up browned, by infrared rays.
    Couldn't our bodies harness the chemical energy as it breaks down the food, and turns it into other kinds of energies? Also doesn't the toaster cause the Maillard reaction, isn't that chemical change, or is it just chemical change that is not producing chemical energy? ( < probably). I don't really know any other way this could be chemical in the toasting process. It sounds like I shouldn't have it in at all.

    3. Electrical to radiant and thermal energy. Is that better?
     
  11. Jan 22, 2018 #10

    haruspex

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    Excellent point.
    That was already in the bagel. Toasting does not add any.
    I think it does not add chemical energy.
     
  12. Jan 22, 2018 #11
    So basically chemical energy does not belong. It should look like this:

    3. Electric to radiant and thermal energy.

    [QUOTE="haruspex, .Thermal energy can be listed because no conversion is 100% efficient. There is is always some friction, or resistance in electrical cables, etc., though whether the question expects you to worry about that I am not sure.[/QUOTE]

    This isn't very advanced physics, will they take off points if I do have thermal energy listed? For other things they have told me not to worry about the extra energy, but they didn't mention anything here......
    In their example they talked about wind turbines and said,'Energy transformations: kinetic energy of air to kinetic energy of turbine to electrical energy.' We discussed 4 types of producing electricity (wind, solar, biomass, and tidal) and what the energy transformations for those where. Only in biomass did thermal energy come up. What do you think about including or not including thermal energy in my answers?
     
  13. Jan 22, 2018 #12

    haruspex

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    Sounds like you can safely omit it for 1 and 2, though obviously not for 3.
    For 3, where do you think most of the heat energy ends up?
    By the way, purists say heat only relates to the transfer of energy. When something is hot, we say it has internal energy.
     
  14. Jan 23, 2018 #13
    Well, I don't know if you read this:
    But these are the only types I was supposed to work with.

    Am I still missing one?
     
  15. Jan 23, 2018 #14
    Does that mean heat energy is not something I should have in there?
     
  16. Jan 23, 2018 #15

    haruspex

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    Sorry, my post was a bit confusing.
    As I wrote, heat only refers to transfer of energy. Once it has been transferred it takes the form of internal energy. Thermal energy is a special case of internal energy; it only relates to temperature changes. When ice at 0C melts to become water at 0C it has gained internal energy but not thermal energy.

    If you were told to consider thermal energy, but not internal energy, that is a bit of a problem for the toasting bagel. But perhaps you have not been introduced to the concept of internal energy, so it is all being called thermal.
    Anyway, can you answer my question, given that hint. Where did most of the energy end up?
     
  17. Jan 23, 2018 #16
    Maybe in the air??? Kinetic energy??? I really don't know.

    And yes I was not introduced to internal energy. Does that make a difference?
     
  18. Jan 23, 2018 #17

    haruspex

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    Which is heavier, a toasted bagel or an untoasted one? What has happened?
     
  19. Jan 23, 2018 #18
    The toasted bagel is lighter. It has dried out. The water/ moisture has been removed. Are you saying an energy symbolizes this? Because I can't figure out which one.
     
  20. Jan 23, 2018 #19

    haruspex

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    Yes. This is the latent heat of vaporisation, which is internal energy but not thermal energy.
    When water is heated, the molecules move faster. This is thermal energy. But they still stay close to each other, held by the hydrogen bonds. As further heat is added, some of the molecules escape. The work done against those bonds in escaping is internal energy, but it isn't thermal energy because the molecular speed does not increase.

    I suggest that in bagel toasting that is where most of the energy ends up.
     
  21. Jan 23, 2018 #20
    But they didn't teach me about internal energy so I shouldn't put it in, right?
     
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