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Convert kinetic energy into thermal energy

  1. Apr 12, 2012 #1
    Hi, I need a way to convert kinetic energy into thermal energy as well as the specific heat of the entire Earth's atmosphere. The idea is to see if the heat generated by many meteoroid fragments could possibly account for any climate change.
    Thanks.
     
  2. jcsd
  3. Apr 12, 2012 #2

    mfb

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    1 Joule of meteorite energy will give approximately 1 Joule of heat in an impact.

    80% nitrogen, 20% oxygen are a good approximation.

    However, your approach cannot work. The atmosphere is not an isolated system, it constantly exchanges energy with space and with the surface of the earth. Think about day and night: The temperature differences show you how much energy is exchanged every day. This is several orders of magnitude larger than any long-term climate changes.
    It is better to consider the equilibrium temperature*: The atmosphere will reach this very quickly and follow it, if it changes.
    Meteorite impacts do not change the equilibrium temperature, as soon as their produced dust is gone (only relevant for really large impacts).

    *averaged over natural cycles like days and years. If you want to do it right, this can get quite tricky, but it is possible.


    Short answer:
    No. And your approach to calculate it does not work.
     
  4. Apr 12, 2012 #3

    sophiecentaur

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    As a first approximate approach you could estimate the total energy from meteor fragments and then do two calculations for equilibrium temperature- one using just the Sun's energy input and the other using the Sun's energy plus this extra bit.
    That would just give you the mean surface temperature of a uniform sphere with no atmosphere. I suspect that the difference would be very small (cf 1kW/msquared) so you could then just add this small difference to the temperature 'everywhere'.
    You wouldn't need to go into the complications of weather etc. unless the result of this very simple model was significant.
     
  5. Apr 12, 2012 #4

    mfb

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    But then we need an increased impact rate to change the temperature.
    Anyway, the incoming energy is extremely small compared to the radiation from the sun.

    I found an upper estimate of 10000 tons per day, with ~40km/s this gives a total energy of 8*10^15J. This is the energy the earth gets from the sun within 50 milliseconds. The solar radiation adds 2 million times more energy than meteors, even with this high number of incoming material.
     
  6. Apr 12, 2012 #5

    sophiecentaur

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    I guess that's game set and match against global warming by meteors then.
     
  7. Apr 12, 2012 #6
    Somebody at Wiki needs a proofreader ....
    http://en.wikipedia.org/wiki/Solar_radiation
    The sad part is that this will be copy and pasted to several more sites as it seems to be ONE author being the source of information word for word.

     
  8. Apr 12, 2012 #7

    mfb

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    Apart from the redundancy, where is the problem in the quoted part?
    Uncertainties at the numbers would be nice, but if you really need these values for actual scientific work, take the references given there.
     
  9. Apr 12, 2012 #8
    Did you not notice the 1.366 kW/m² vs 1361 W/m² thats sloppy on the author's part not uncertainty.
     
  10. Apr 13, 2012 #9
    First, let's just try and see how much energy the Earth's atmosphere would gain. THEN, let's consider how much energy the Earth loses and gains over time.

    Do you have a link to that I could look at?
     
  11. Apr 13, 2012 #10

    sophiecentaur

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    What counts is the TOTAL energy arriving at the Earth if you want to find the final surface temperature. Whatever you have on the surface (cloud, black paint or shiny tinfoil) the equilibrium mean temperature due to Solar Energy ends up the same so start with the simplest model to see if it's worth going on with this.

    The Earth is not in Deep Space, light years from any source of Energy; it is right next to the Sun. As stated earlier in this thread, the Solar energy arriving on Earth is millions of times greater than the Kinetic Energy from Meteorites so the effect on mean surface temperature is absolutely minimal - certainly undetectable. What point is there in proceeding further?
     
  12. Apr 13, 2012 #11

    mfb

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    Did you notice that these are two different measurements? It is explained in the quoted part.

    @forumasker:
    Wikipedia with reference to abc.net.au

    This is about two orders of magnitude smaller than the number I used in my calculation.
     
  13. Apr 13, 2012 #12
     
  14. Apr 13, 2012 #13
    I would really like some actual answers out of this entire forum rather than random bickering, because if 951 Gaspara can't even raise Earth's temperature 1 degree after all it's energy was converted to thermal energy, and I calculate it would have transferred 4.94*10^18 joules of thermal energy, then I can say for sure meteoroids can't really effect the climate at their current rate.
     
  15. Apr 13, 2012 #14

    sophiecentaur

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    You have been getting answers but not taking them in. The equilibrium temperature is reached when the total energy in is balanced by radiated energy out. It is a nonsense to ignore the Solar input. Compared with the solar input, the meteor input is vanishingly small.
    Is that not a reasonable answer? If not, what's wrong with it?
     
  16. Apr 14, 2012 #15

    mfb

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    And 1366W/m^2 = 1.336kW/m^2, as dots are used as decimal mark.


    @forumasker: You can use the mass of 951 Gaspara, use the ~40km/s as approximation (might be different for this specific object, no idea), and use the total mass of the atmosphere with the given approximation of 80% nitrogen, 20% oxygen. Use 1kg/cm^2 and the surface of the earth to estimate the total mass of the atmosphere. If you have problems at a specific step, ask about that.
    In addition, a large impact produces a lot of dust, which actually cools the planet.
     
  17. Apr 14, 2012 #16

    sophiecentaur

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    I don't understand why the characteristics of the atmosphere are a vital part of this calculation. The Whole Earth gets the energy and the mean temperature increase will depend upon the total thermal capacity, eventually. (A massively long time constant, but we have millions of years to play with here.)
     
  18. Apr 14, 2012 #17
    You forgot that Earth not only gets but also loose energy and that atmosphere is quite close to steady-state. It is not like a cold room warming up by a heater but like a warm room that already reached its maximum temperature because it loose as much energy through the walls as it gets from the heater. The steady-state temperature of the room is mainly influenced by the power of the heater and the property of the walls. The heat capacity is irrelevant. In case of the climate Sun is the heater and the atmosphere is the wall.
     
  19. Apr 14, 2012 #18

    sophiecentaur

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    I meant that thermal capacity affects the rate of temperature change. I see that I didn't put it it very well. But I still don't see why the atmosphere is getting so much attention.
     
  20. Apr 14, 2012 #19
    Only for fast temperature changes (e.g. between day and night) but not for a long term process like climate change.
     
  21. Apr 14, 2012 #20

    sophiecentaur

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    How about seasonal changes? A gardener would know that.
    But I still don't understand the preoccupation with the atmosphere in this thread.
     
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