Re: [Phys-l] Conservation of energy in nuclear reactions

[Spinozalens@aol.com]

In a message dated 5/1/2009 3:21:31 PM Eastern Daylight Time,  
Spinozalens@aol.com writes:


In a  message dated 5/1/2009 3:12:19 PM Eastern Daylight Time, Spinozalens  
 
writes:


On  Friday, May 01, 2009 11:54 AM, John Denker  wrote:

> Part of the  energy is mc^2.  We call this the  _rest energy_.
> I suppose you  could define potential energy to be  equal to 
> the rest energy, but  not everybody does.  Also  there are 
> issues with the  gauge-dependence of typical notions  of 
> potential  energy.

OK

> Let's be  clear:  The equation E=mc^2  applies in the rest 
> frame of  the particle.  This is Einstein's  original meaning 
> of the  equation, and also the meaning that has  been 
> conventional among  those who do relativity for a living, and  
> has been for several  decades that I know of.  (I am aware  
> that from time to  time there have been attempts to define 
>  some notion of  "relativistic mass", but this is a Bad 
>  Idea./2/)  Mass (m)  means rest mass, so it is redundant but 
>  harmless to call it  "rest" mass.  

Agreed.

> Bottom  line:  Energy  is conserved.  Period.  There are no 
>  known  exceptions.  Of course to make this work you need to 
>   include all forms of energy, including the rest energy  mc^2.

Still,  the question is whether this form of energy is *in  addition to*
the  energies we considered previously (like the  gravitational energy  or
whatever) or *instead of*.  That is what  I am confused about and  how I
could simply explain this to  non-scientists.

Consider an  astronaut dropping a rock on the  moon.  While the rock is
falling,  how does the kinetic energy of  the moon/rock/astronaut change?
How does  the rest energy of the  moon/rock/astronaut change?  Are there
any  other forms of energy  that are  changing?





))))))))))))))))))))))))))))))))))))))))

The  energy of the rock is constant before it hits the surface. Being held  
 
above the surface it has all of its energy as potential energy. (   
ignoring 
thermal, etc.) As it falls it converts its potential energy  to  kinetic ene
rgy of motion, the sum of the kinetic and potential  being  constant. ( 
Hamiltonian) When it hits the surface all of  former energy of  motion (at 
this 
point is has zero potential energy)  is converted to  molecular energy 
(heat, 
sound, etc.) Energy is  conserved at all times.

Bob Zannelli  







This ignores air friction which will actually  cause some of rock's energy  
to be converted to molecular energy,  heat, sound. 


Bob Zannelli 






Oh the moon. No air, never mind.
 
Bob Zannelli 
**************Access 350+ FREE radio stations anytime from anywhere on the 
web. Get the Radio Toolbar! 
(http://toolbar.aol.com/aolradio/download.html?ncid=emlcntusdown00000003)