Re: [Phys-L] defining energy

[John Denker <jsd@av8n.com>]

On 10/30/2013 09:30 AM, Bruce Sherwood wrote:

> Is it that you're alluding to the fact that the "translational
> kinetic energy" 0.5M_sys*v_cm^2 is different from the sum of all the
> kinetic energies of the particles that make up the system,
> sum(0.5m_i*v_i^2)?

Yes.

> Or is there more to your comment than I'm understanding?

Nothing more.  I'm widely known for my keen grasp of the obvious.


==============================================
In a different sub-thread:

On 10/30/2013 11:25 AM, jbellina wrote:

> I call it the egg yoke
> theory of energy production, crack the egg and yolk comes out, crack
> the molecule and the energy comes out.

That's a fairly standard name for this misconception.  It is
indeed a wide-spread and deep-seated misconception.  Chemistry
teachers tear their hair over it.

I do *not* have a good handle on how to teach this topic.  The
most constructive thing I can say at the moment is another memo
from the keen-grasp-of-the-obvious department:  It helps to draw
the picture:
   http://www.av8n.com/physics/mass.htm#sec-binding-ke

In an energy-level diagram, the so-called "binding energy" is
measured down from the top.  Almost anything else you would think 
of as "energy" is measured up from the bottom.