🚀 go-pugleaf

  ... note followups to relativity newsgroup ...


Russell Blackadar <russell@REMOVEmdli.com> writes
}
} Matthew Wootton wrote:
} > This means that as you give an object energy (e.g., by increasing it's
} > speed) you increase the mass of the object.
} 
} No, increasing an object's linear speed will *not* increase its
} mass.  You have to increase the energy in its center-of-mass
} inertial frame, and just moving the center of mass (albeit faster
} or slower) obviously won't do that.

Matthew Wootton <matt@akooka.demon.co.uk> writes:
>
>I'm *so* glad you picked me up on that. This confused me, as it implies
>that energy is relative. 

 Energy _is_ relative. 

  An aside: if you are holding a ball while in a car, the KE of the 
  ball is zero to you, but very large to an observer in another frame. 
  If a stone gets kicked up from the pavement, its KE is very small 
  to an observer standing by the road, but very large to your window. 

 That is why he made the distinction about mass being the total energy 
 in the center-of-momentum frame (aka rest frame of the body). 

-- 
 James A. Carr   <jac@scri.fsu.edu>     | Commercial e-mail is _NOT_ 
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