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

Energy and matter

  1. Jan 28, 2004 #1
    can someone give me an accurate and comprehensive synopsis of the relations between energy and matter. i suppose i mean say, kinetic energy vs potential energy stored in bonds and energy as speed increases as mass increases... things like that. pretty much relating the two.
  2. jcsd
  3. Jan 29, 2004 #2
    Hey, im not jimmy, but hey anyway. Afraid i cant help you though.
  4. Jan 31, 2004 #3
    well anything would be helpful... i seriosuly can't understand how both concepts don't perplex everyone else... i've looked through my physics book... and there isn't much... i dunno.. just hoping someone has a firm grasp on both ideas and would care to share their wisdom...

    Hi andy
  5. Jan 31, 2004 #4


    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    The releationship between mass and energy is contained only in relativity theory, which is considered rather advanced physics.

    In short, the more energy something has, the more mass it is. This goes for gases at higher temperatures, spacecraft at higher speeds, and so on.

    The equation of merit is:

    [tex]E = \sqrt{m c^2 + p^2 c^4}[/tex]

    Where [itex]E[/itex] is energy, [itex]m[/itex] is rest-mass (the mass something will appear to have when it's at rest with you), [itex]p[/itex] is the momentum the object has, from your viewpoint, and [itex]c[/itex] is the speed of light.

    In other words, just as you already know, energy can be manifested by motion. A bullet flying at you is a lot more frightening than one laying on the ground. The only thing that relativity adds is the assertion that mass itself is also a form of energy.

    - Warren
  6. Jan 31, 2004 #5


    User Avatar
    Science Advisor

    As an example, when a thermonucelar device is detonated, nuclear fusion occurs. This means that the nuclei of hydrogen atoms (single protons) are smashed together so hard that they overcome their magnetic repulsion, and get close enough for the "strong nuclear force" to hold them together, making hellium atoms (two protons stuck together). But here's the interesting bit; the comined mass of the two protons stuck together is slightly less than one would get by adding the masses of the seperate protons. Where did this tiny bit of mass go? It is the energy of the explosion!

    I once read that according to the simplified version of Einstein's famous equation (E=mc2), one pound of matter will release as much energy as a million gallons of gasolene. But that huge amount of energy still has the same mass as it did when it was in the fom of matter. And in supercolliders, matter is brought into existance by the concentration of large amounts of energy.

    I like to think of matter and energy being the two forms in which mass can exist. Conversion from one to the other form is possible, but the total mas remains the same. It's a bit oversimplified but hey, I like the simple life!
  7. Feb 1, 2004 #6
    mk... i get most all of that, and i'm reasonably familar with relitivty and all... at least theoretically... hmm..

    ok, so how does something have energy?
  8. Feb 1, 2004 #7


    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    Energy is the ability to do work. If you can somehow make something lift something up, or make a light bulb light up, then that something has energy.

    - Warren
  9. Feb 2, 2004 #8
    right, i know... nevermind
  10. May 20, 2004 #9
    It comes from a few different sources:
    - all matter is a form of condensed energy; if you break a particle into 2 smaller particles whose net sum is less than the original, energy actually ballances out the remaining mass - it's actually converted
    - as chroot said, if something already has energy, (like a body in motion), that energy will remain until it is lost through work, (i.e. friction, opposing force, heat, etc.).
    - there are native forces that we don't yet understand, (like gravity), that convert to energy, (i.e. to bodies pulled by gravity end up with kenetic energy). electrons and protons both have native electrical charges, and there are numerous other properties that we just don't understand completly... yet!

    hope that's a little more clear

    the future master of the universe, (i hope! :)
  11. May 20, 2004 #10
    ok, so how does something have energy?

    Energy is defined by its ability to change something and in the process
    of so doing be changed itself.But the total energy before and after
    a change is induced is always the same.
  12. May 21, 2004 #11


    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    Let's forget relativity for a while.

    Mechanical energy such as KE or PE are very directly dependent on mass. For instance the kinetic energy is proportional to the mass of the object and the square of its speed. The gravitational potential energy of an object is also proportional to its mass. Besides gravitation, there are other causes of potential energy. All of these result from some kind of force or interaction between your object and something else. Since the gravitaional force depends on mass, so does the gravitational potential energy. But if you considered the electrostatic force between charged objects, there is found to be no dependence on the mass there. This is macroscopically manifested in ...say a spring.

    The energy stored in a compressed spring depends (largely) only on the extent of compression and the elastic properties of the material of the spring. These elastic contants result from the electrostatic forces between the atoms (what you refered to as 'bonds'). Hence you find that the mass of the spring plays no role in its potential energy.

    Another manifestation of this 'bonding energy' is melting. In a solid, the atoms are bonded to each other through electrostatic forces. When you heat the solid, you are putting energy into it. For a while, you find that adding heat only makes the atoms jiggle about faster. In toher words, you are increasing the kinetic energy of the atoms. This is what you are quantifying (the average KE of the atoms) when you measure the temperature of the solid. Suddenly, at some point, you find that you've put in enough energy into the atoms that they can escape the electrostatic attraction that was keeping them together in a dense lattice. This is what melting is : you are breaking the chemical bonds between the atoms and allowing them to move about freely, hither and thither, frequently bumping into each other but still having energy enough to fly away.
  13. Jul 12, 2004 #12
    I have a question, if u completely converted a piece of matter into energy, would ALL the energy be in the form of a high frequency electromagnetic wave, for instance gamma rays ?
  14. Jul 12, 2004 #13
    When you annihilate matter and antimatter, that's what you get. Two gammas, actually, because you must conserve momentum.
  15. Jul 13, 2004 #14
    [tex]E = \sqrt{m0^2 c^4 + p^2 c^2}[/tex]
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?

Similar Discussions: Energy and matter
  1. Matter to energy (Replies: 18)

  2. Properties of matter (Replies: 1)

  3. Matter of fact (Replies: 2)

  4. Manipulation of Matter (Replies: 2)