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Velocity translating into weight?

  1. Aug 26, 2009 #1
    I accidentally posted this under another forum user's topic, sorry about that :frown:

    My question was regarding matter gaining mass when it is accelerated. My question originated from an explanation of the large hadron collider; the explaination stated that when the protons in the LHC are sped up to 99.9% the speed of light, instead of gaining more speed, they get heavier. Someone posted that everything gains mass when it is accelerated, but there is no significant change until near light speed. How does this added energy translate into weight? The particles themselves are only individual protons, how does one proton gain weight, and where does that weight come from? I'm completely in the dark about this, so if my question doesn't make sense, please set me straight, thank you.
  2. jcsd
  3. Aug 26, 2009 #2
    I also heard it mentioned that matter and anti matter can be created with just energy, how?? What form does the matter and anti matter take? When/if they recombine, does it generate the same amount of energy that was required to create it, or are there byproducts of the whole anomaly?
  4. Aug 27, 2009 #3


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    Increases speed means increased energy and energy has mass: e= mc2.
    Note that, since speed must be measured relative to some "stationary" frame of reference, the increase in mass is also relative to that frame of reference. If you were moving along side the proton at 99.9% the speed of light, you would not measure any increase in the mass of the proton.
  5. Sep 6, 2009 #4
    That's not exactly right: they do get more speed, and objects with more speed have more mass, so they also get heavier (from our point of view, at least).

    The mass comes from the increased speed! This is just a fact in relativity. Energy and mass are the same stuff, so making something move faster gives it more kinetic energy and therefore more mass, since they're the same stuff. When someone says "the mass of a proton is (some standard number)" they are referring to the mass of a proton at rest. Since kinetic energy is a form of mass too, the weight is different if you "weigh" it while it's moving!

    "How" is a big question... there's a whole area of physics there. But one example is a collision between particles in a particle collider. Energy becomes matter there.

    Any form that is consistent with the laws of physics. One collision might get you some mesons, and another might get you a handful of other weird particles, like muons and whatnot. As long as all the relevant laws, like conservation of energy and conservation of momentum are satisfied, just about any random particles can be produced.


    Of course, a particle collision doesn't usually produce just matter and antimatter, it also produces a lot of pure energy particles like photons.
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