Re: Kinematic equations (Was: Crib Sheets)

[John Gastineau <johng@pcep-physics.physics.ncsu.edu>]

At 03:25 PM 3/29/96 -0600, >Tom K. McCarthy wrote:
> On Fri, 29 Mar 1996, Jim Green wrote:
>
> > Rick, et al., what is worse is that they come to think "g" is acceleration
> > when it has nothing to do with accelerstion.  And they then stick "g" in
> > anywhere acceleration is required.
> Then you know they really do not understand the very basics upon which an 
> adequate understanding of the concepts is based.  You are nearly back to 
> square one with, hopefully, just a very few students.  This is where a 
> good solid 8th grade course in physical science becomes most effective.


We don't help our students very much by our use of language. How often do
our students hear "the acceleration due to gravity" in the context of little
g? We use units of acceleration on it, too, so it MUST be "the"
acceleration! We're our own enemies. 

I have taken to telling my students to "watch their language" when they use
such phrases. Little g is more properly called the local gravitational
constant, and it has a value of 9.8 N/kg, not 9.8m/s^2. 

You can also free them of this problem by thought experiments. What if the
local gravitational force were given by F= (local gravitational constant) *
squareroot(mass) and all other physical laws unchanged? Now repeat Galileo's
Pisa experiment. Which hits the ground first, the light ball or the heavy
one? It's an eye opener. After getting carefully reasoned predictions, I
simulate this strange universe in Interactive Physics. It gets their attention. 

JEG


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John E. Gastineau                                PV34PV3P
North Carolina State University Physics
Physics Courseware Evaluation Project
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