Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

What is energy

  1. Aug 19, 2005 #1
    A few questions about energy... I'll start with this:

    Is energy simply kinetic interactions between matter BY matter? My understanding is that chemical and heat are both electromagnetic and are simply photonic flux.
  2. jcsd
  3. Aug 19, 2005 #2
    It's a scalar quantity associated with the state of a system. That's a pretty vague definition, but since we're in the QM forum, I think it's appropriate.
  4. Aug 19, 2005 #3
    A state of a system

    Meaning the position of matter within that system, correct?
  5. Aug 19, 2005 #4
    There's more to it than position. But since this is a QM forum,
    energy numerically defines the frequency of something.
    We don't know know what that something actually is but mathematically
    it looks like this:

    [tex] \Psi = e^{i\frac{E}{\hbar}t} [/tex]
  6. Aug 19, 2005 #5
    Frequency suggests a fluxuation of material density... doesn't it?
  7. Aug 19, 2005 #6
    Nobody knows what energy is.

  8. Aug 20, 2005 #7
  9. Aug 20, 2005 #8


    User Avatar
    Science Advisor

    "Energy" is a book-keeping device. It was noted pretty early on in physics that in simple collisions, two quantities mass*velocity and 1/2 * mass* velocity2 stayed the same which made them easy to use- one was called "momentum" and the other "kinetic energy". It was observed that the speed of an object (and so it's kinetic energy) increased as it fell, decreased as it went up. "Potential energy" was defined in order to keep "total energy" constant. Of course, if you added friction, you no longer had conservation of those energies but could observe that the temperature increased proportional to the lost energy. Okay, "heat energy" keeps the book keeping straight! As of the advent of relativity, because "e= mc2", we had to include mass itself as a kind of energy!
  10. Aug 20, 2005 #9
    Nice post HallsofIvy. You are probably aware of this but that does not define energy. It only defines a property of energy. You'll note that total momentum also satisfies the property you just described.

    I took a crack at this topic here


    Last edited: Aug 20, 2005
  11. Aug 21, 2005 #10
    first of all i'd like to point out that heat is not electromagnetic, Microwave is electromagnetic.. Heat is the vibration of particles in a substance...

    secondly....... its late and i am too tired to finish this post.... *laught out loud* hopefully i'll remember to add another concluding post later... Goodnight
  12. Aug 21, 2005 #11
    oh by the way i mentioned microwave,. because it transfers into heat energy ... *Microwave* ovens use microwaves to heat up food... check out some articles on "howstuffworks.com" that website has some real good information on electromagnetic waves.. light and radio,. energy... a great information source for this kind of thing... Hopefully HowStuffWorks will be able to answer your question,. as i am too lazy and tired right now
  13. Aug 21, 2005 #12
    I would put it like this:

    Energy is a class of mathematical combinations of quantitative aspects of one system and its enviroment which forms a way to compute the maximum work that can be done by this system on the parts of its enviroment.

    Best Regards

  14. Aug 21, 2005 #13
    In my opinion, the best definition of energy would be embedded within M-Theory.

    Masoud Zargar
  15. Aug 21, 2005 #14
    Could you please write this best definition of M-theory ?

    Best Regards

  16. Aug 21, 2005 #15
    Maybe we should ask the Department of Energy?
  17. Aug 22, 2005 #16
    im getting sick of this question. ppl ask what energy/matter/charge is. this are proepties matter and things have. its not like its particles that sourond other particles
  18. Aug 22, 2005 #17
    Well, Zelos, this is a little different. There isn't a Department of Matter or a Department of Charge.
  19. Aug 22, 2005 #18


    User Avatar

  20. Aug 22, 2005 #19
    And there's a State Department. Can't tell if it obeys Pauli Exclusion, though. They all look the same.
  21. Aug 23, 2005 #20
    According to Feymann, energy is just a book-keeping device with the very useful property that energy is conserved. The conservation of energy comes from the fact that experiments are time symmetric (aka "things do not depend on the absolute time.)

    Edit: I can't spell Feynman
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook