Re: weight vs. mass (was: Units and Conversions)

[John Clement <clement@HAL-PC.ORG>]

> [regarding weight versus mass] ...
> > Should I just go along or teach them properly?  My inclining
> > as a physicist is to teach them correctly but realistically
>
> Seems like an easy choice.  There are advantages to the
> correct approach, and no disadvantages AFAICT.
>
> > I don't think they are going to get it.
>
> What makes you think that?
> What's not to get?
>
> Suppose astronaut A tosses a banana to astronaut B
>   http://www.christiananswers.net/kids/banana.avi
> Is the banana weightless? T/F

Depends on whether you define weight as the gravitational force on it or the
measurement done with a spring scale.  This has been the subject of many
unresolved debates on this list.

> Is the banana massless?   T/F
> Does Newton's second law apply to the banana? T/F

The students that Tina is talking about are not physics students, and have
no clue.  They are not even taking algebra in the course she asks about.

> See also:
>   http://www.monmouth.com/~jsd/physics/weight.htm


Unfortunately, the "what's not to get", is the point of view of a formal
operational thinker about understanding constructed by concrete operational
students.  The fact is that they don't get it.  The students think very
differently than the way we do, so some topics which seem extremely obvious
to us are not obvious to them.  I agree that it is worthwhile trying to make
the distinction, but ....  The MOP curriculum spends quite a while on this
distinction, and the teachers manuals point out in great detail the various
difficulties that the students have.

The real difficulty stems from the fact that weight and mass are not
directly observable as say a chair of a table is.  This puts in the class of
being a theoretical concept, as are most physics concepts.  Anton Lawson has
shown that theoretical concepts are much more difficult and that the ability
to understand rises as the thinking level of the student rises.  He has even
proposed that there is a level above formal operational called theoretical.
This is the level at which understanding of theoretical concepts becomes
easy.  Presumably this list has a majority of theoretical thinkers.

Please notice that the class in question is "applied math" which is likely
to have a majority of concrete operational, some transitional, and no formal
operational thinkers.

John M. Clement
Houston, TX