Re: [Phys-L] defining energy

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

This is a HUGE misconception that virtually all students come into class
with.  As I said, part of the problem is the phrase "breaking bonds" which
conjurs up a rubber band breaking and releasing energy.  Most biology books
reinforce this by saying that you get energy in the Krebs cycle by breaking
bonds.  The bio books ignore the subsequent process of hydration where
forming bonds releases more energy than it took to break the initial bonds.

I try very hard to get students to visualize bonds like rubber bands that
merely stretch and become thinner.  Also the idea of working to pull
something apart reinforces the concept that when you stretch a bond you put
in energy.  This is a tough misconception that even professional biologists
may have.

John M. Clement
Houston, TX

> Following up on John Clement's comments about gasoline and 
> oxygen, I found when teaching a distance education version of 
> Matter & Interactions for in-service high school physics 
> teachers that many of them were surprised to discover that 
> they had been carrying around a view of binding energy that 
> was basically backwards, with the wrong sign. The view was 
> something like "there is energy stored in the bonds in the 
> gasoline molecules which we can use" instead of "in 
> combustion the molecules transition to a lower energy state 
> and become more bound". To put it another way, they seemed to 
> have thought that "more" in the bonds (more binding) meant 
> more "bond" energy was available, instead of more bonding 
> being associated with lower energy, not higher.
>
> I'll admit I can't express the issue very clearly, but the 
> teachers themselves were convinced that useful energy 
> resulting from transitions to lower energy levels (greater 
> binding) was a new idea for them.