Re: Nitpicking: gravity is not a force???

[Mervin Koehlinger <tchkoehlimw@crf.cuis.edu>]

On Sat, 8 Aug 1998, Doug Craigen wrote:

> What if I was to ask a class "what are the forces acting on this
> block?"?  Well, there is the force due to tension in the cable, the
> force due to friction between the block and the table, the force due to
> gravity ...
>
> Is this acceptable as an alternative to saying "the force of gravity"? 
> Is there a way of saying "normal force" other than to completely rename
> it as "the force due to contact with the table"?  Or is "normal force"
> ok - like "frictional force" or "gravitational force"?
>
> If we say that "there are four fundamental forces" is incorrect - what
> do we propose to say instead?  How about "there are four fundamental
> sources of force"?

What does it take to make a force?  Answer: there must be an interaction
between two distinct objects.  I would suggest that you can be confident
that you have a force if you can name the object that is exerting the
force and the object that experiences the effect of the force.  If you
can't do that, you don't have a force.

In my class we name forces in just that way.  Yes, it takes a bit longer,
but it is worth it for the improved understanding, including the skill of 
sketching free-body diagrams. For example: what are the forces on a block
being towed along a table?  Answer: (1) the force by the earth on the
block, (2) the normal force by the table on the block, (3) the tension by
the rope on the block, (4) the force of friction by the table on the
block.

Very rigorous, very simple, very clear.

Mervin

Mervin Koehlinger
Physics Instructor
Concordia Lutheran High School
Fort Wayne, Indiana