Chronology Current Month Current Thread Current Date
[Year List] [Month List (current year)] [Date Index] [Thread Index] [Thread Prev] [Thread Next] [Date Prev] [Date Next]

Re: [Phys-L] treating force as a vector ... consistently

As long as I never refer to actions or reactions (I actively oppose this
the first day we talk about forces in my courses) and that I specify the
following:

1) The two forces which constitute a Newton's Third Law Pair must act on
different bodies
2) They must be of the same kind (friction, gravitation, contact forces,
etc)
3) When considering the state of motion of a body, one must consider all
the forces on (and only the forces ON) that body by any other agent

then the only confusion comes about when students fail to apply these
concepts; and that confusion has historically been very rare.

We have spent a long time going round and round in this discussion - but
really, it's not that hard. We just have to be careful about the language
we use, and drum it into the students to avoid the typical high school
teaching on this matter.

Todd


On Sat, Aug 20, 2016 at 7:10 PM, Anthony Lapinski <alapinski@pds.org> wrote:

This has been an interesting discussion! The way I see it, the third law is
about action-reaction pairs: A on B and B on A (in opposite directions). So
if weight (Earth pulling down on book -- A on B) is the action, then the
reaction is the book pulling up on the Earth -- B on A. This was my
original question. But if the book pushing down on the table is the action,
then the table pushing up on the book is the reaction. Seems simple and
unambiguous to me. I do realize the upward vectors have the same numerical
value, but they are different reaction forces (book on Earth vs table on
book).

On Sat, Aug 20, 2016 at 6:55 PM, Richard Heckathorn <geepaw@wowway.com>
wrote:

Greetings, I've read each of the interesting discussions dealing with
Newton's laws, vectors, etc.

Over my years of teaching I have put together some power points dealing
with the topics. I'm just wondering how much is OK and how much needs
revision.


If you go to my website listed below select a column Operation Physics.
Select 06 Newtons third law and then 06 investigations, power points and
articles.

What I am referring to is some of the power points that I have included.
Any revisions needed?

So I sit back and wait for the responses.

Have a Great Day

Website rheckathorn.weebly.com



On Aug 20, 2016, at 6:35 PM, Bob Sciamanda <treborsci@verizon.net>
wrote:

Scalars, Vectors and Tensors are MATHEMATICAL entities - used as
calculational models of physical properties.
There is a dangerous, but natural tendency to reify these MATHEMATICAL
entities. Fight it!

-----Original Message----- From: Bob Sciamanda
Sent: Saturday, August 20, 2016 6:19 PM
To: Phys-L@Phys-L.org
Subject: Re: [Phys-L] treating force as a vector ... consistently

Correction:

My paraphrase should read:
It makes no sense to tell students that NUMBER is
a QUANTITY and then turn around and ask them to distinguish a NUMBER
"here" from a NUMBER "over there". It is a crime against the laws
of mathematics.

Bob Sciamanda
Physics, Edinboro Univ of PA (Em)
treborsci@verizon.net
www.sciamanda.com


-----Original Message----- From: Bob Sciamanda
Sent: Saturday, August 20, 2016 6:09 PM
To: Phys-L@Phys-L.org
Subject: Re: [Phys-L] treating force as a vector ... consistently

JD complained:
"It makes no sense to tell students that force is
a vector and then turn around and ask them to distinguish a force
"here" from a force "over there". It is a crime against the laws
of mathematics."

Let me paraphrase this remark:
It makes no sense to tell students that QUANTITY is
a NUMBER and then turn around and ask them to distinguish a QUANTITY
"here" from a QUANTITY "over there". It is a crime against the laws
of mathematics.

Like QUANTITY, VECTOR is a mathematical entity used as a calculational
MODEL
to represent a property of an entity.
Just as the QUANTITY 2 can represent a property of my legs, the same
QUANTITY 2 can represent the number of major American political
parties -
so the VECTOR F can represent several different forces (equal in
magnitude
and direction). They are identical mathematical entities, but are used
as
models of different physical entities.

Bob Sciamanda
Physics, Edinboro Univ of PA (Em)
treborsci@verizon.net
www.sciamanda.com

_______________________________________________
Forum for Physics Educators
Phys-l@www.phys-l.org
http://www.phys-l.org/mailman/listinfo/phys-l


_______________________________________________
Forum for Physics Educators
Phys-l@www.phys-l.org
http://www.phys-l.org/mailman/listinfo/phys-l

Bob Sciamanda
Physics, Edinboro Univ of PA (Em)
treborsci@verizon.net
www.sciamanda.com
_______________________________________________
Forum for Physics Educators
Phys-l@www.phys-l.org
http://www.phys-l.org/mailman/listinfo/phys-l

_______________________________________________
Forum for Physics Educators
Phys-l@www.phys-l.org
http://www.phys-l.org/mailman/listinfo/phys-l

_______________________________________________
Forum for Physics Educators
Phys-l@www.phys-l.org
http://www.phys-l.org/mailman/listinfo/phys-l




--
Todd K. Pedlar
Associate Professor of Physics
Luther College, Decorah, IA
pedlto01@luther.edu