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If enough heat is applied to an object, will it reach escape speed?

  1. Nov 20, 2013 #1
    This is just something I'm wondering, if we apply enough heat to an object, and since the speed of the molecules inside it is directly measured by temperature, will the molecules inside the object move fast enough to reach the escape speed of the planet that it is on? I know that this is the case for why many planets don't have an atmosphere (because their escape speed is too low to hold an atmosphere due to their weak gravity) and I'd also think that when enough heat is applied to a solid object, it turns into a gas and (if heated enough) will continue rising up above the planet's surface until it "breaks free" of the planets gravity, thus, reaching escape velocity. Although, I don't know if these assumptions are true.
     
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  3. Nov 20, 2013 #2
    Uhh no. If you apply heat to an object, it will vibrate more. You won't change it's speed.
    However, heated gas becomes more dilated, so, depending on the mass of the planet, it can escape - but not because it reached escape velocity

    Also, the correct term is escape velocity, not speed.
     
  4. Nov 20, 2013 #3

    ZapperZ

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    I don't know what you mean by "escape speed" here, but you might want to look up "thermionic emission". That is a common electron source used in old TV and CRT tube and old diodes. The heated filament is the electron source.

    However, applying this to celestial bodies is a completely different matter and physics.

    Zz.
     
  5. Nov 20, 2013 #4
    What? I'm talking about the molecules moving faster (in km/s for gasses) inside the object if it is being heated, not the actual object moving as a whole... well, it does move as a whole through states
    I learned that from a homework assignment that I had for astronomy - the question talked about the moon Titan and the molecules inside its atmosphere having a speed of about 0.4 km/s (while Titan's escape velocity is 2.6 km/s I think), the question asked me to compare the molecules' speed with Titan's escape velocity and the speed needed for the molecules in its atmosphere to evaporate (or move faster than Titan's escape velocity so that they evaporate/escape Titan)
     
    Last edited: Nov 20, 2013
  6. Nov 20, 2013 #5
    I mean the escape velocity (you guys get too hung up on terminology, I know its important too but try to focus more on the meaning) of a planet, and I also don't see what "thermionic emission" have to do with what I'm asking, it would be helpful if you can elaborate.
     
    Last edited: Nov 20, 2013
  7. Nov 20, 2013 #6

    ZapperZ

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    First of all, I wasn't the one who was "hung up" on the terminology.

    Secondly, I was giving an example of how electrons can escape a solid simply via heat, which is analogous to what you were asking.

    Thirdly, you might want to consider the fact that "objects" melt or vaporize at some point as you increase the temperature. So consider the average KE at those critical temperatures.

    Finally, molecules, atoms, and particles of such size do not have free, unimpeded travel from earth's surface to the upper atmosphere to escape, even if it has enough speed to escape the earth's gravity in the first place. The presence of air means that it will have a mean free path that is sufficiently short, it won't be able to travel far before it encounters collisions with other particles.

    Zz.
     
  8. Nov 20, 2013 #7
    I see that english is not your native language. It is not my native language either, but anyway, that question does not make any sense. Titan's atmosphere is made out of gas (obviously, duh). So how can it evaporate? And what does speed have to do with that? Only liquids can evaporate
     
  9. Nov 20, 2013 #8
    So what you mean is that when molecules obtain more speed due to the increased temperature, they will just collide more with each other and not actually change their place as a 'whole'? Because I was thinking that the reason why gasses rise in the air is because their molecules are moving faster than a solid or a liquid object on the ground (which I think leads to lighter or heavier density, but that's another story), which also means that the faster the molecules move (or the higher the temperature), the higher the gas will rise above the surface; although, I could (and probably) be completely wrong, which is why I'm asking you guys. And also, I did "consider the fact that 'objects' melt", I stated in a previous post that "objects move through states".
     
    Last edited: Nov 20, 2013
  10. Nov 20, 2013 #9
    Here is the question exactly: "Saturn’s moon Titan is the only moon in the solar system with an atmosphere, which is 95% nitrogen molecules (N2), similar to Earth’s atmosphere. At Saturn’s distance from the Sun, the temperature of the atmosphere is only 95 K (−180C), and the molecules have an average speed of about 0.4 km/s. How does this speed compare with the speed needed for the molecules to escape from Titan and evaporate into space? Show how you got your answer."

    p.s I've been speaking English for over 8 years now, so I'll try not to take that as an insult (I also don't see how my English is inferior in anyway, but that's not the focus here).
     
  11. Nov 20, 2013 #10

    ZapperZ

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    This appears to be a HW/Coursework-type question. If this is the impetus of your question, then you've posted it in the wrong section. You should have started with this in the very beginning, rather than asking a rather puzzling question, and you should have posted this in the HW/Coursework forum.

    Zz.
     
  12. Nov 20, 2013 #11

    russ_watters

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    Regardless of the framing, the question points to a discussion of how our atmosphere got its current composition:
    The molecular weight and temperature of molecules does indeed determine their speed and if the speed is high, they can indeed escape. That's why our atmosphere has few light gases and Mars is almost entirely carbon dioxide.

    For large objects, there is no bulk motion, so the idea does not apply.

    Confused framing or not (that's why the question is being asked!), this is not a complicated or controversial enough subject to have been worthy of such aggressive replies. Calm down and consider who you are talking to, people.
     
  13. Nov 20, 2013 #12
    ... Ok, here's what happened: I started with this question about a week ago and I needed help with it so I did post it in the homework section to ask for help. But, after I finished the assignment and got all the help I needed (a few days ago), I started thinking more about the question and thought that the concept implied in the question (which is the relation between molecules' speed and escape velocity) could also be applied to all objects. So, to feed my own curiosity, I decided to post the question that I thought of here (in this section), but my question originated from the assignment question that I posted, but it is not directly related to it at all.
     
  14. Nov 20, 2013 #13

    russ_watters

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    I prefer "escape speed" because "escape velocity" wrongly implies that direction matters.
     
  15. Nov 20, 2013 #14
    That's exactly what I was saying, that "if the speed is high, they can indeed escape" the celestial body that they are on. Therefore, with high enough temperature (combined with low molecular weight), a gas can reach and go beyond escape velocity, right? But what I'm not sure of is that if escape velocity can be reached by the increased speed of molecules (within the gas), which would lead the gas to escape from the planet.
     
  16. Nov 20, 2013 #15
    I know that that is not directly aimed at me but I apologize if I was being aggressive in any way (which I'm sure I wasn't), that is not my goal here.
     
    Last edited: Nov 20, 2013
  17. Nov 20, 2013 #16
    Oh, so basically what you are saying is that hotter gases will get less dense and will move faster towards space, right? If so, Ramon's question makes sense. But if you heat the whole atmosphere equally, nothing will happen but dilation.
     
  18. Nov 20, 2013 #17

    jbriggs444

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    The point is that lighter gasses (such as hydrogen and helium) at a given temperature will have a larger fraction of their component molecules at a speed greater than escape velocity. So you can heat the atmosphere evenly and while most or all of hydrogen can escape [over geological time periods] the fraction of the carbon dioxide that escapes over the same period will be much less.
     
  19. Nov 20, 2013 #18
    So I was right all along when I said that the molecules' speed within a gas (doesn't just have to apply to an atmosphere) can reach and will go beyond the escape speed of the celestial body that the gas is on. I know that molecular mass (not 'weight', as terminology is important) also causes changes in the speed of molecules too, but I was trying to focus more on temperature.
     
  20. Nov 20, 2013 #19

    ZapperZ

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    See, this is where it gets confusing, and why it seems that this topic is being approached differently by different people.

    To me, the term "escape speed" means that the minimum speed needed for something to escape the gravitational field starting from the surface of the earth! But from what I'm seeing, it seems that this includes molecules escaping that are already in the upper atmosphere. Is that true? But is this what is defined as "escape speed" here? It certainly isn't how we defined it in standard classical mechanics.

    If it is from the surface of the earth, then I will once again bring out the issue of the non-infinite mean-free path for such particles trying to escape.

    Zz.
     
  21. Nov 20, 2013 #20

    russ_watters

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    No, it has nothing to do with density. It is about molecule speed relative to escape speed/velocity.
     
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