1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Matter and energy

  1. Mar 2, 2009 #1
    ello


    first of all appologies for my fuzzy knowledge and termanology, its been nearly ten years since I have studied physics in any form.

    Watching a BBC documentry the other week 'Star on Earth?' with Prof. Brian Cox, he talked of how a gram of matter has the same amount of energy as that which is released during a nuclear explosion (I think this must be comparing to one of the early nukes).

    Now I believe also that when matter is cooled to absolute zero it ceases to exist as all the matter has been converted to energy, though this has never been proven.

    Given these two facts, surely to cool all the equipment of the CERN LHC to near absolute zero must require extracting unthinkable amounts of energy?

    My understanding is that temperature and energy have a linear relation. So to heat a mass by one degree requires a fixed amount of energy regardless of the starting temperature of the mass (assuming constant pressure and that the mass is not at the cusp of changing state).

    My question then is does cooling a mass to nearly 0°K really require extracting as much energy as a nuclear explosion per gram, or is there some kind of latent heat/energy of existence, similar to the energy overhead required to change the state of matter e.g. the latent heat of fusion? Perhaps latent heat of tactility would be more descriptive for this case.
     
  2. jcsd
  3. Mar 2, 2009 #2

    Doc Al

    User Avatar

    Staff: Mentor

    This is not true at all. When cooled to absolute zero, the molecular kinetic energy of a substance is at a minimum, but that doesn't mean that "matter has ceased to exist" or that "matter has been converted to energy". (Where did you hear this wild claim?)
     
  4. Mar 2, 2009 #3
    How can something that's "never been proven" be considered fact?
     
  5. Mar 2, 2009 #4
    The amount of energy stored in matter is given by E=mc2. The only variable in there is the mass, temperature doesn't factor in. The amount of thermal energy matter has depends on the specific heat of whatever it is. 1kg of water at 0 C has 1,142,778 J in thermal energy. The same kg of anything has 8.98755179 * 1016 J of energy for it's mass.
     
  6. Mar 4, 2009 #5
    I thought it was only in the gas theory that when a gas was cooled to absolute zero the mass would be nil and would in theory it would not exist, however even this was not proven and clearly should not happen so it is only an ideal gas that would?

    Cooling to absolute zero does require a lot of effort absolute zero as far as i know has never been reached, it is hard to find ways of removing energy without giving it more energy.

    As far as i know temperature and engery always increase at a set amount if one increases, whats the proportion that the other will increase in?

    I always thought that the probelm with cooling mass to 0°K was the fact that it is hard for the engergy to be moved from that mass as it has become so low.

    I am asuming you are right with the fact that it will require alot of energy to cool a mass to 0°K, how much energy is required i am not sure about but if it did require the same engergy as a nuclear explosion would this be safe at all?
     
  7. Mar 4, 2009 #6

    Doc Al

    User Avatar

    Staff: Mentor

    Nope, not true at all. Even "in theory". Mass doesn't just disappear when you cool something.
     
  8. Mar 4, 2009 #7
    The tests on gases show that the mass decreases so in theory should it not be able to reach nil?
     
  9. Mar 4, 2009 #8

    Doc Al

    User Avatar

    Staff: Mentor

    Please provide a reference for this statement so I can understand what you are talking about.
     
  10. Mar 4, 2009 #9
    I think i'm getting confused with the ideal gas theory which states

    "The state of an amount of gas is determined by its pressure, volume, and temperature."

    which would give the equasion "pV = nRT"

    am i right so far?
     
  11. Mar 4, 2009 #10

    Doc Al

    User Avatar

    Staff: Mentor

    Well, PV = nRT is the ideal gas law.
     
  12. Mar 4, 2009 #11
    yes so if the temperature was low enough would the mass of the gas be reduced to a point where it has a volume of nil?
     
  13. Mar 4, 2009 #12
    Note: I am not an expert by any means. I'm a sophomore in college, so my statements should be elementary at best. I've studied physics in school as well as in my free time, but I'm sure I've probably understood several things incorrectly. If a more learned member would confirm or deny my claims, it'd be much appreciated. However:

    I noticed in this discussion some say "no thermal energy = no mass because mass = energy". However, I think the confusion lies in saying "thermal energy = energy". If you extract energy (thermal or kinetic) from a substance, only a fraction of that energy actually comes from the mass itself, and I think this energy is only due to relativistic effects. A mass at 0.0001K will still have a large portion of its mass left. Now I suppose if you were to convert the entire mass into energy and then extract that, then there'd be no mass left... but that's called an explosion.
    -DT
     
  14. Mar 4, 2009 #13
    so if you keep pressure and volume constant and increase the temperature to infinity you will end up with zero moles!?

    just kidding.

    to answer the initial question: there is an enthalpy of formation, but this is commonly considered zero for elements. work is required to displace the enviornment by whatever volume the object takes up. The closest thing I can think of to this "energy of tactility" would either be E=mc^2 or the enthalpy of formation.
     
  15. Mar 4, 2009 #14

    Doc Al

    User Avatar

    Staff: Mentor

    The volume going to zero does not mean that the mass goes to zero. (Realize that real gases will deviate from the ideal gas law at these limits, anyway.)
     
  16. Mar 4, 2009 #15
    ohhh i see now sorry, i'm doing an essay on xenotransplantations at the moment so i'm a bit muddled with this, but i think i understand now thanks for you clarification.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: Matter and energy
  1. Energy to matter (Replies: 5)

  2. Matter and Energy (Replies: 8)

Loading...