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

Changing Mass

  1. Dec 29, 2006 #1
    I've heard that when an object is accelerated at huge huge speeds they actually gain mass. Is there a formula to see how much mass an object would gain will going a certain velocity.
     
  2. jcsd
  3. Dec 29, 2006 #2

    Hootenanny

    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    I quote RandallB, since this topic was somewhat discussed in this thread recently.
    The important concept to note here is that it is the momentum which increases, not the 'mass'. In my opinion, in special relativity only invariant mass should be considered and the whole notion of 'relativistic' mass should be abandoned in special relativity (the situation in general relativity is somewhat more complex). As Randall says above, the notion that mass increases is usually introduced when explaining the 'basics' of relativity in a general context, but leads to misunderstandings when it comes to formally learning relativity. Below are some links which you may wish to peruse;

    Invarient Mass
    Relativistic Mass
    Relativistic Mechanics
     
  4. Dec 29, 2006 #3
  5. Dec 29, 2006 #4
    after reading those links, then let me see if I understand:

    mass has 2 situations:

    invariant mass, that, independent from the observer, it has a defined value.
    relativistic mass, that depends on observer.

    relativistic mass is "transformed" by lorentz factor.

    invaritant mass, isn't "tranformed", and it is normally the mass that we use in classical mecanics, in expressions like: density=m/V, kinectic E=1/2mv^2, potential E=mgh and so1.

    relativistic mass, is used in modern mecanics, and is too "named" as energy, by the E=mcc.

    both masses can be used in momentum expression(p=mv)

    in case of photon, it has no invariant mass, but as it have energy, we must assume it as relativistic mass

    am I right about this??
    Regards, littlepig
     
  6. Dec 29, 2006 #5

    Janus

    User Avatar
    Staff Emeritus
    Science Advisor
    Insights Author
    Gold Member

    [itex]E = mc^2[/itex] gives the energy equivalence of the invarient mass.
     
  7. Dec 29, 2006 #6
    so that's why, in my post, this one

    i couldn't say the energy released by hidrogen in man "B" couldn't be greater than in man "A". The invariant mass doesn't varies, because velocity doesn't take efect on invariant mass....humm....getting it...:tongue2:

    thank you for your help and links...
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?