In the problem of the marshmallow moving at the speed of light, didn't you forget about its kinetic energy?

Sure I did. I only included the rest mass energy because for the real world, it is hard to accelerate large objects to speeds higher than 1/2 the speed of light, and it is only at those speeds that the kinetic energy term becomes important relative to the rest mass. The total energy is just:

 2              2         2
E     = ( mc^2 )    + (pc)

or
              2
E = gamma x mc

where

                     1
   gamma =    -----------------
                             1/2
             ( 1 - (v/c)^2 )
 

OK...If you want to suppose that you could accelerate a marshmallow to the speed of light, you end up with a gamma = infinity, and it's for sure that the Earth is a gonner. Then again, to get the marshmallow to that speed exactly, you will have had to 'burn up' the entire universe and then some to give the marshmallow this speed. Even a marshmallow traveling within 1 percent of the speed of light, will have a gamma of only 12.2 ! This is enough to give engineers a headache, and barely enough to cause a medium-sized crater!


Copyright 1997 Dr. Sten Odenwald
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