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

["John S. Denker" <jsd@MONMOUTH.COM>]

John Clement wrote:
> ... The fact is that [students] don't get it.

Some of them do.  By far the majority of them do.
They weren't born knowing it, but they figure it out.
This thread started out referring to a college class.

...
> The real difficulty stems from the fact that weight and mass are not
> directly observable as say a chair of a table is.

This cannot possibly be the real reason for "not getting it".

If you want to get picky about it, the human body comes
equipped with rather direct means for perceiving forces
such as weight.  Mass can be perceived almost as directly
by shaking a high-mass low-friction object such as a massive
pendulum.

The perception of "chair" is not "built in" -- it is most
certainly a learned perception, and an indirect one at that.
If you doubt me, try the following exercise:  suppose you
had invented the first chair.  Write the patent.  Define
chair, and describe how it differs from the prior art.  If
you think this is easy, you're not paying attention.

I would suggest that whatever difficulties students have
for considering chairs simpler than forces arise from other
reasons; plausible hypotheses include:
 -- Chairs (excluding benches) are discrete, not continuous.
 -- Chairs (excluding benches) are scalars.
    (one chair, two chairs, et cetera)
 -- In contrast, forces are vectors and come in a continuous
    distribution of directions and magnitudes.
 -- We usually don't ask very challenging questions about
    chairs, but we ask detailed and intricate questions
    about forces.
 -- et cetera.