Re: [Phys-l] order of topics (was Newton's first law)

[Hugh Haskell <haskellh@verizon.net>]

At 10:56 AM -0500 11/3/11, Bill Nettles wrote:
> I'd like to see comments of a proposed re-ordering of topics that 
> I've been thinking about. In the topics of gravity and electricity 
> we usually introduce the forces first. For gravity we start out with 
> the force that a planet (usually Earth) exerts on a mass, m, and 
> state
>
> F_ = mg_ (the "_" indicates a vector).
I think a more pedagogically valid approach is to start with 
momentum, in the from of collisions. This is a very concrete approach 
that students can get a "hand-on" feel for. We don't need the details 
of the collisions, just the before and after information. This can 
lead to the concept of force as "the thing needed to change motion," 
and the collisions lead pretty naturally to the Third Law. A more 
careful approach to considering force in collisions can suggest the 
Second Law, and then bringing in the First Law as a logical 
consequence to the other two and make the connection with history.

In this way, the abstractions are saved until the end, when the 
students have developed a bit of "intuition" about how objects 
interact. Once they get there, the resistance to accepting the idea 
of the First Law is largely gone.

Hugh
--

Hugh Haskell
mailto:hugh@ieer.org
mailto:haskellh@verizon.net

It isn't easy being green.

		--Kermit Lagrenouille