Re: [Phys-l] teaching energy

["John Clement" <clement@hal-pc.org>]

No, viewpoint number 2 is not valid.  If gravitational potential energy can
not be in the ball because the presence of the Earth is necessary for there
to be GPE.  Now it is certainly associated with objects (note the plural),
but then you have #3.

When you focus on the ball as the place where the energy is located, the
student loses sight of the fact that the Earh is necessary as a reference.

The idea of putting energy into a system, is certainly valid, but this is
very abstract and is not understood well by beginning students.  The field
does not have to be mathematically defined, but can be invoked as the
connection between objects.  It becomes the "container" in which the energy
resides.  Students have not trouble with understanding that energy is in a
spring or rubber band.

Notice that in doing this the field is simply the name for the mechanism
that pulls the ball to the Earth, and the Earth to the ball.  It is the
invisible "rubber band".  It is not waaay to complicated.  It actually helps
the student visualize the fact that there is also a force on the Earth, and
helps with acquisition of Newton's third law concepts.  Actually this
provides a partial anchor and bridging analogy for NTN 3.

Now with kinetic energy, the energy is in the object.  With thermal energy,
the energy is in various physical places such as the two objects that are
rubbing against each other...

Unfortunately the idea of energy in a system looks like handwaving to lower
level intro. students, but it might be more appealing to the higher level
thinkers than a mysterious field.  So when one talks about it, both ideas
can be mentioned.  In either case the field implies a system, so it provides
a mental connection between the objects, and helps the students understand
the idea of system.

The idea that you just present the math is what most traditional courses
have done, and the research shows that it loses most of the students.  They
are adrift with no mental model.  Indeed, the research is now showing that
even in QM and advanced courses, that the standard approaches are not
helping students develop mental models.  So just presenting the math may
only generally work for individuals who already have mental models that go
with the particular equations, and can transfer those models to the new
situations.

John M. Clement
Houston, TX

> On 10/03/2006 09:48 AM, Robert Cohen wrote:
> > I've been skimming through the posts and I think there are three points
> > of view:
> >
> > 1. Energy is associated with fields.
> > 2. Energy is associated with objects.
> > 3. Energy is associated with systems of objects.
>
> I agree.
>
> All three viewpoints are valid, and can be considered a chain of
> successive approximations, in the order (1), (3), (2).