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Thread: heat question

  1. #1 heat question 
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    If a solid is repeatedly placed under deformative stress but does not infact deform will the repeated stresses result in a rise in temperature within the solid?


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    Yep.


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    That's what I thought. No one seems to consider tidal forces as a contributer to the internal heat of the earth. It seems like it should be a large heat inducer. When I brought it up on the astrophysics board I was told that since the earth was not deformed then there was no heat generated. That did not seem right to me.
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    What? Any astrophysicist knows that there are ample examples of tidal forces generating heat in our own solar system. Not so obvious with Earth, but more so with other bodies.

    https://en.wikipedia.org/wiki/Tidal_heating

    http://www.planetaryexploration.net/...l_heating.html

    Etc...
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  6. #5  
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    Quote Originally Posted by Sealeaf View Post
    That's what I thought. No one seems to consider tidal forces as a contributer to the internal heat of the earth. It seems like it should be a large heat inducer. When I brought it up on the astrophysics board I was told that since the earth was not deformed then there was no heat generated. That did not seem right to me.
    Er, hang on. If the object under stress does not deform, then no work is done and no increase in temperature will result. There has to be some "strain", i.e. movement in response to the applied stress. W = F x d, right? d=0 => W = 0.

    The practical point, though, is that nothing is in reality totally rigid. So the Earth does deform a bit and that will create heat. I feel fairly sure I read somewhere that tidal heating is thought to be quite significant on some of Jupiter's moons, for example.

    (I see that while I was typing this pyoko has made the same point.)
    Last edited by exchemist; March 10th, 2014 at 11:07 AM. Reason: final sentence added
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    I don't know who would say there is no tidal deformation of the Earth. Geologists count it as a form of noise but use it fairly often in calculations of earth movements. It is a large enough movement to be measurable.

    Even the Hyperphysics textbook mentions it.
    Tidal Friction

    Here is Wikipedia on it too.
    Earth tide - Wikipedia, the free encyclopedia
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    In fact, it's stealing tiny amounts of kinetic energy from the Moon's orbit and that's what eventually results in tidal locking of the rotation and revolution periods. And, eventually, in billions of years or so, the Moon's orbit coming inside Roche's limit and the Moon being disintegrated into a ring.

    And of course there is massive deformation of the oceans. You should try pointing that out to them. Sounds like they forgot.
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    Where my thought was going is that we are aware that a strong magnetic field seems to be important to maintaining a favorable environment for life. The strong magnetic field is generated by a fluid iron core spinning within the earth. High internal heat drives volcanism and the magnetic field both of which contribute to maintaining a life supporting atmospher. If the presence of a large satellite is a major contributor to keeping a moving fluid core and thus a life favorable planetary environment, then this is a powerful clue to look for in seeking earth like worlds. ie : not just small, rocky and in the "Goldy locks zone" but also having a large companion body.
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  10. #9  
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    Quote Originally Posted by Sealeaf View Post
    Where my thought was going is that we are aware that a strong magnetic field seems to be important to maintaining a favorable environment for life. The strong magnetic field is generated by a fluid iron core spinning within the earth. High internal heat drives volcanism and the magnetic field both of which contribute to maintaining a life supporting atmospher. If the presence of a large satellite is a major contributor to keeping a moving fluid core and thus a life favorable planetary environment, then this is a powerful clue to look for in seeking earth like worlds. ie : not just small, rocky and in the "Goldy locks zone" but also having a large companion body.
    I presume you mean the role of the magnetic field is to shield us from energetic particles. However my understanding is that the major contributor to the Earth's internal heat is decay of radioisotopes, rather than tidal forces.
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    That the source of Earths internal heat is from the decay of radioisotopes is indeed stated in the literature but I have never seem much evidence supporting this. It is more stated as an explanation of the heat that is known to exist, rather than an actual proof that the heat is due to radioactive decay. The fact of the center of rotation of the Earth/moon system being located thousands of miles away from the axis that the Earth is spinning on has got to be violently stressful. I have a visual of a bicycle with a broom stick through the spokes of the drive wheel.

    If the presence of a large companion body is necessary for the development of Life, then life may be a lot more rare in the universe than we would assume just looking at the number of "sun" like stars. Which in turn is an explanation of the Fermi Paradox.
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    Quote Originally Posted by exchemist View Post
    Quote Originally Posted by Sealeaf View Post
    That's what I thought. No one seems to consider tidal forces as a contributer to the internal heat of the earth. It seems like it should be a large heat inducer. When I brought it up on the astrophysics board I was told that since the earth was not deformed then there was no heat generated. That did not seem right to me.
    Er, hang on. If the object under stress does not deform, then no work is done and no increase in temperature will result. There has to be some "strain", i.e. movement in response to the applied stress. W = F x d, right? d=0 => W = 0.

    The practical point, though, is that nothing is in reality totally rigid. So the Earth does deform a bit and that will create heat. I feel fairly sure I read somewhere that tidal heating is thought to be quite significant on some of Jupiter's moons, for example.

    (I see that while I was typing this pyoko has made the same point.)
    One other point I'd like to make on this subject is that you can have deformation without generating heat if you do not exceed the elastic limit of the material. The heat is generated when the material is permanently deformed.
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    Quote Originally Posted by Harold14370 View Post
    One other point I'd like to make on this subject is that you can have deformation without generating heat if you do not exceed the elastic limit of the material. The heat is generated when the material is permanently deformed.
    Harold, as you know, my grasp of even elementary physics is tenuous at best, however this runs counter to my practical understanding. Perhaps something else is going on that I'm not grasping.

    In oilfield drilling we frequently use downhole motors that generate rotation and torque by passing the drilling fluid through a power section. This consists of a lobate stator within which is a lobate rotor with one fewer lobe. The difference in lobes creates a series of cavities down which the mud passes and in so doing converts the hydraulic energy of pressure and flow to mechanical energy of rotation and torque. The rotor is of steel and the stator of an elastomer. When operating the elastomer experiences flexing that leads to a temperature build up, one of the key design and operating issues of these motors. However the elastomer is not permanently deformed. This seems to run counter to what you are saying. Where am I going astray?
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  14. #13  
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    Quote Originally Posted by John Galt View Post
    Quote Originally Posted by Harold14370 View Post
    One other point I'd like to make on this subject is that you can have deformation without generating heat if you do not exceed the elastic limit of the material. The heat is generated when the material is permanently deformed.
    Harold, as you know, my grasp of even elementary physics is tenuous at best, however this runs counter to my practical understanding. Perhaps something else is going on that I'm not grasping.

    In oilfield drilling we frequently use downhole motors that generate rotation and torque by passing the drilling fluid through a power section. This consists of a lobate stator within which is a lobate rotor with one fewer lobe. The difference in lobes creates a series of cavities down which the mud passes and in so doing converts the hydraulic energy of pressure and flow to mechanical energy of rotation and torque. The rotor is of steel and the stator of an elastomer. When operating the elastomer experiences flexing that leads to a temperature build up, one of the key design and operating issues of these motors. However the elastomer is not permanently deformed. This seems to run counter to what you are saying. Where am I going astray?
    Good point. If you compress a gas in a cylinder, adiabatically (so no heat is lost) the temperature of the gas goes up during compression and returns to what it was when the stress is removed. So long as the insulation is perfect, the process is reversible. If you compress a perfectly elastic solid spring, then you would say the work done goes into potential energy stored in the spring. But can we exclude the possibility that there might also be an element of adiabatic temperature rise, as there is in the gas case? Far less of course, as it is a solid and won't compress so much, but is it really zero?
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    Quote Originally Posted by exchemist View Post
    Good point. If you compress a gas in a cylinder, adiabatically (so no heat is lost) the temperature of the gas goes up during compression and returns to what it was when the stress is removed. So long as the insulation is perfect, the process is reversible. If you compress a perfectly elastic solid spring, then you would say the work done goes into potential energy stored in the spring. But can we exclude the possibility that there might also be an element of adiabatic temperature rise, as there is in the gas case? Far less of course, as it is a solid and won't compress so much, but is it really zero?
    It says here that rubber acts a lot like a gas in the way that it stores energy.
    Rubber elasticity - Wikipedia, the free encyclopedia
    The result is that an elastomer behaves somewhat like an ideal monatomic gas, inasmuch as (to good approximation) elastic polymers do not store any potential energy in stretched chemical bonds or elastic work done in stretching molecules, when work is done upon them. Instead, all work done on the rubber is "released" (not stored) and appears immediately in the polymer as thermal energy. In the same way, all work that the elastic does on the surroundings results in the disappearance of thermal energy in order to do the work (the elastic band grows cooler, like an expanding gas). This last phenomenon is the critical clue that the ability of an elastomer to do work depends (as with an ideal gas) only on entropy-change considerations, and not on any stored (i.e., potential) energy within the polymer bonds. Instead, the energy to do work comes entirely from thermal energy, and (as in the case of an expanding ideal gas) only the positive entropy change of the polymer allows its internal thermal energy to be converted efficiently (100% in theory) into work.
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    Wikipedia has a good article on the Earth's internal heat budget: Earth's internal heat budget.

    The total heat emerging from the Earth's interior is about 47 TW. The total incoming solar radiation is about 173,000 TW. The internal heat is about 0.03% of the total.

    The heat is a combination of primordial heat from the Earth's creation and a substantial contribution from internal radioactivity. Rock is a very good insulator, and although radioactivity is low, there's just so dang much of it. Our entire biosphere is this thin scum on top of all the hot rock. If the Earth were a ball 20 feet across the entire distance from the bottom of the Challenger Depth of the Marianas Trench, to the top of Everest, would be thinner than a coat of paint.
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  17. #16  
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    Quote Originally Posted by Sealeaf View Post
    That the source of Earths internal heat is from the decay of radioisotopes is indeed stated in the literature but I have never seem much evidence supporting this. It is more stated as an explanation of the heat that is known to exist, rather than an actual proof that the heat is due to radioactive decay. The fact of the center of rotation of the Earth/moon system being located thousands of miles away from the axis that the Earth is spinning on has got to be violently stressful. I have a visual of a bicycle with a broom stick through the spokes of the drive wheel.

    If the presence of a large companion body is necessary for the development of Life, then life may be a lot more rare in the universe than we would assume just looking at the number of "sun" like stars. Which in turn is an explanation of the Fermi Paradox.
    I'd like to hear you actually articulate your idea properly, instead of just hinting at what it might be.

    Are you saying you think that radioactivity may not be important and that therefore the Earth's core would have solidified, causing the loss of the protective magnetic field, were it not for tidal heating effects from the moon? Or if not, then what?

    If that is what you are saying, there are several things we can explore to test your hypothesis. One is to look at the heat balance and work out what rate of decay in the moon's orbit would be needed to provide the necessary degree of heating. Then we could find out whether this is astronomically significant and if it tallies with astronomers know of the history of the moon's orbit. My guess is won't stand up, or it would have been part of the theory already, but we can see.

    Until that is settled, it seems to me that the speculation you seem to be so keen to get onto, about the putative importance of satellites to life, is not worth considering.
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    Quote Originally Posted by Schneibster View Post
    In fact, it's stealing tiny amounts of kinetic energy from the Moon's orbit and that's what eventually results in tidal locking of the rotation and revolution periods. And, eventually, in billions of years or so, the Moon's orbit coming inside Roche's limit and the Moon being disintegrated into a ring.

    And of course there is massive deformation of the oceans. You should try pointing that out to them. Sounds like they forgot.
    The moon is retreating. Its orbit increasing in exchange for a slowing Earth.
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    Indeed. I'm not sure how the moon is meant to be stealing kinetic energy from the Earth when the Earth is busy transferring angular momentum to the moon. Perhaps what you mean Schneibster, is that theoretically once tidal lock between the two bodies is achieved, then the moon reverses and begins to approach the Earth. However the timing for this places it billions of years after both have been destroyed by the expansion of the sun at the end of its life.
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    Nuclear reactions in the earth are much more important than the tidal forces.
    Evidence of locations that had ore bodies capable of forming natural reactors indicates the nuclear heating was stronger in the past too because more of the fissionable isotopes were available to decay and produce heat.

    http://large.stanford.edu/courses/2013/ph241/masters2/

    The idea of a naturally-occurring fission reaction had been postulated in 1953 by Wetherwill and Inghram and further studied in 1956 by Kuroda. [2,4,5] As discussed elsewhere, the Gabon sites (16 in total, between the Oklo mine and the neighboring Okelobondo uranium mine) satisfied the conditions (e.g., appropriate size, presence of a moderator, and absence of neutron poisons) that had been proposed for natural fission reactors. [1] One criterion is particularly of note - while a modern, natural uranium deposit could not become a reactor due to its decreased U-235 content (0.720 percent), at the time that the Gabon reactors were operational, natural uranium contained approximately 3 percent U-235. This higher concentration enabled the self-sustaining fission reactors; in fact, it is comparable to the level of U-235 enrichment of the uranium fuel used in most modern nuclear power stations. [2]
    Last edited by dan hunter; March 16th, 2014 at 01:54 AM. Reason: problems pasting wiki quote
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