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Energy types

  1. Aug 11, 2012 #1
    hello!

    I would like to know, which are all the energy types, force types, field types, wave types, particle/material types?

    i ask this, because i was told recently that van der walls forces/field/energy is not electric (either electrostatic or electromagnetic)

    thanks!
     
  2. jcsd
  3. Aug 11, 2012 #2

    Bobbywhy

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    Gold Member

    mather, I think you don't need anyone to list "all the energy types, force types, field types, wave types, particle/material types" to get answers. For a clear overview of Van der Waals forces have you studied this yet?
    http://en.wikipedia.org/wiki/Van_der_Waals_force

    If you learn everything on this page you can get to more detailed explanations by clicking on those "blue" (links) terms within the article and also by using the references at the end.

    There are lots of other sources of explanations using "Google" search.
     
  4. Aug 16, 2012 #3
    I still cant get it.
    What else can be, if not gravity, electricity, electromagnetism?
     
  5. Aug 16, 2012 #4

    Drakkith

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    Staff: Mentor

    Kinetic energy, thermal energy, electrical energy, and a dozen other terms. All of it really boils down to the 4 fundamental forces. We just use more terms to refer to specific examples of energy to make it easier to work with.
     
  6. Aug 16, 2012 #5

    Bobbywhy

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    Gold Member

    mather, I am not an expert, but as I read these sources it seems that the van der Waals forces are indeed mediated by electrical fields...both attraction and repulsion.

    “van der Waals forces
    The attractive or repulsive forces between molecular entities (or between groups within the same molecular entity) other than those due to bond formation or to the electrostatic interaction of ions or of ionic groups with one another or with neutral molecules. The term includes: dipole–dipole, dipole-induced dipole and London (instantaneous induced dipole-induced dipole) forces. The term is sometimes used loosely for the totality of nonspecific attractive or repulsive intermolecular forces.”
    http://goldbook.iupac.org/V06597.html

    Here are a few more websites for you to study:

    http://hyperphysics.phy-astr.gsu.edu/hbase/chemical/waal.html
    http://www.chemguide.co.uk/atoms/bonding/vdw.html
    http://antoine.frostburg.edu/chem/senese/101/liquids/faq/h-bonding-vs-london-forces.shtml

    Finally, here is an easy to read and excellent description of the van der Waals force:
    http://www.britannica.com/EBchecked/topic/622645/van-der-Waals-forces
     
  7. Aug 26, 2012 #6
    in deed this is excellent and concise

    the question is... do I miss something that I still think these forces are due to electric charged subatomic particles, thus they are electrostatic/electromagnetic?
     
  8. Aug 26, 2012 #7
    Mather,

    Perhaps if you posted the exact nature of what you were told?

    Did you respondent mean that Vander Walls and (London) forces are the result of statistical averages of short term electrical interactions, in much the same way that pressure is the result of short term momentum interactions in gasses?

    Or did she mean that the Van Der Walls equations was the first to recognise that a correction to the ideal gas equation was necessary to acount for the fact that molecules occupy space?

    Or.....?
     
  9. Aug 26, 2012 #8
    sorry but this is not the english i can comprehend
     
  10. Aug 26, 2012 #9
    Please post exactly what was said.
     
  11. Aug 26, 2012 #10
    That van der wals are not electric forces.
    There is a possibility that he said van der wals are not electrostatical or maybe electromagnetical forces.
     
  12. Aug 26, 2012 #11
    So do you understand the kinetic theory of gasses about how the pressure on the walls comes about?
     
  13. Aug 26, 2012 #12
    I suppose it is because of the thermal/Brown movement of the molecules of the gas.

    I dont know what is the source of that kinetic energy. I know that it increases with heat. But I dont know the quantum/submolecule mechanism of it.
     
  14. Aug 26, 2012 #13
    The kinetic theory is not a quantum or any fancy upmarket theory.

    It is just about representing the molecules as little balls bouncing around.

    As they bounce around they will bump into each other and into the container walls.

    As they bounce around they have a range of velocities and the velocity of individual molecules changes as they bump into things.

    As with any range of quantities we can represent this by an average velocity.

    Bumping into each other only causes changes within the gas so we are not interested in that here.

    Bumping into the walls, however, exerts a force on the walls. the greater their velocity the greater their impact force.

    Since there are lots of molecules we can calculate an average force using the average velocity.

    We call this average force the pressure.


    The point of all this is that we can attribute the pressure of say 5 pascals to the average effect of the momentary bumping of the molecules in to the walls.

    I hope this helps because VDW forces have a similar average basis which we can move on to.
     
  15. Aug 26, 2012 #14
    That's wrong; Van der Waals forces are indeed electromagnetic.
     
  16. Aug 26, 2012 #15
    Okay then I understand that van der wals are actually electromagnetic forces

    Their source is the movement of electrons around the nuclei of a molecule, which movement makes the molecule be a specific dipole, tripole, etc (according to the structure of the molecule) at a specific time.

    As for thermal energy, how does it increase the kinetic energy of a molecule?

    Which is the velocity of a molecule in void or where there is no thermal energy at all?
     
  17. Aug 26, 2012 #16
    I don't know what to say since your response doesn't seem to have anything to do with my last post.

    Am I wasting my time?
     
  18. Aug 26, 2012 #17
    No, i thought that i understood you and i said what i exactly understood in my last post, isnt it correct?

    As for heat and molecular velocities, maybe it's another topic
     
  19. Aug 26, 2012 #18
    The only point I wanted to carry forward was that pressure is an average result of the variable random actions (motions) of a great many molecules. Because it is an averaging process it is statistical in nature.

    Are we OK with that?
     
  20. Aug 26, 2012 #19
    yeah, it seems alright
     
  21. Aug 26, 2012 #20
    Ordinary chemical bonds are fixed
    in length
    in direction
    in strength

    eg the oxygen to oxgen bond in the O2 molecule.

    The bonding electrons are shared equally between each oxygen atom.

    If the two atoms are different eg oxygen and hydrogen in water there is a slight shift of the bonding electron from the hydrogen towards the oxygen.

    We say that the oxygen has greater electron affinity than hydrogen.

    There is a slight unequal sharing of the electron.

    This leads to a permanent small negative charge near the oxygen atom and a corresponding small positive charge near the hydrogen.

    The small negative charge on one molecule interacts with the small positive charge on another molecule.

    This is observed as an intermolecular force we call hydrogen bonding.

    Hydrogen bonding is much weaker than ordinary bonding and is not fixed in length, or direction. Hydrogen bonds come and go as the molecules whizz about.

    But the average effect is as if there were extra weak bonds between the molecules.


    Now consider what a molecule 'sees' as it approaches another one.

    We can use the Bohr model of electrons orbiting a nucleus for this purpose.

    If the electron is on the same side of the molecule as the approaching one it will see a negative charge.

    If the electron is on the opposite side of the molecule as the approaching one it will see a positive charge. (a nucleus)

    Either way there will be an electric interaction of varying stength.

    We call the average of all these interactions Van der Waals forces.

    At greater range they are London forces.

    Yes a more sophisticated way to look at this is to note that the orbiting system forms variable dipoles which interacts with each other.

    That's a lot to chew on, so I'll leave it at that for tonight.
     
    Last edited: Aug 27, 2012
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