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Re: [Phys-l] DATA, FACTS, LAWS, THEORIES



I think I know what "Data" is. And I'll even accept "Confirmed Data" I suppose as a comment that the experimental results are reproducible.

I don't know what "generalized data" is.

I don't know the difference between a theory, a law, a model, a framework, a [insert name]. How does this affect the way I teach or learn physics? It just seems to me that it is an accident of the historical development as to which term is associated with which development in physics -- maybe a measure of the term in vogue at the time of the development. Is the standard model of particle physics a theory? A model? Is there some semantic arithmetic law: 2 theories + 1 law = 1 model? (And if that's true and no one has claimed it, can it be Keller's Law? No wait, Keller's Theory? No wait, arg!)

No one who does physics or who teaches physics should be up at night worrying about these distinctions. So I wonder about the biologists. Is evolution a theory, a law, a model? I question the motivation of those who would have us ponder this, with a line from the movie 1776: "Whatever it is, I'm against it!"

-----Original Message-----
From: phys-l-bounces@carnot.physics.buffalo.edu [mailto:phys-l-
bounces@carnot.physics.buffalo.edu] On Behalf Of LaMontagne, Bob
Sent: Monday, October 19, 2009 12:54 PM
To: Forum for Physics Educators
Subject: Re: [Phys-l] DATA, FACTS, LAWS, THEORIES

The Clausius statement of the 2nd Law of Thermodynamics? Or the Kelvin-Planck
statement?

Bob at PC

-----Original Message-----
From: phys-l-bounces@carnot.physics.buffalo.edu [mailto:phys-l-
bounces@carnot.physics.buffalo.edu] On Behalf Of John Clement
Sent: Monday, October 19, 2009 12:43 PM
To: 'Forum for Physics Educators'
Subject: Re: [Phys-l] DATA, FACTS, LAWS, THEORIES

The relationship in the case of conservation is that the total quantity at
the beginning = total at the end. One writes this as sum (energy before) =
sum (energy after) where you have to list all of the places where the energy
is located. Similarly you write it for momentum. In this case the equation
is implied. Newton's first law is just a reiteration of the second law with
the acceleration set to zero. So sum of forces=0 when acceleration is zero.
The third law is briefly F12=-F21. Lenz law can be stated as an equation.
It is essentially an extension of conservation of energy. Of course it is
an equation with inequality, or one used to find the sign.

I never said 2 variables, I just said variables. Most physics equations
actually have more than 2 variables.

And of course any language rule is proven by the most prevalent cases. But
virtually all language rules have exceptions. So I stand by my definition
as being pretty good, and that is the best you can do with natural language.

In reality, we can only give fairly precise definitions to things we can
measure or derive from measured quantities. Other concepts such as theory,
law, hypothesis can not be exactly defined because one can always find
exceptions in common practice and "things" that are on the dividing line.
And in the end common usage rules.

There is another word, principle, which is sometimes used to refer to the
same concepts, but often not. So some things which are called laws maybe
should be principles, and vice-versa. Both of these provide rules which are
used to determine things in specific situations. I would divide them as
laws being relationships, but principles rules which may not necessarily
imply equations. So Occam's razor is a principle, and definitely not a law.
But there are plenty of murky examples. Now this opens another can of worms
which has already been argued about.

In the end natural language can be argued over endlessly because it is not
subject to proof, or experiment. Anyone who thinks natural language terms
can always be defined exactly is seriously deluded. Some can be more exact,
but others will always be fuzzy. My thought is how do you define a camel?
Then if you look at fossil records, at what point do you decide when an
ancient species is a camel, or not a camel? There is no unique answer to
this, and any answer is by definition. But any definition may have to be
changed as new forms are discovered, so eventually the definition becomes a
book of rules. Life and definitions are often uncertain. The arguments
about theory, law, fact, data, hypothesis are just the current examples of
natural language arguments.

John M. Clement
Houston, TX


"But the one common thing in physics is that all of our laws are
relationships between variables."

How are the Law of Conservation of Momentum or the Law of Conservation of
Energy a relationship between two variables? The two take very different
forms depending on what types of energy are being converted or what type
of
collision is being discussed. Newton's First Law of Motion? Newton's
Third
Law of Motion? Lenz's Law?

Wow, speaking of Lenz's Law, I came across this very cool video:
http://www.youtube.com/watch?v=fxC-AEC0ROk

M. Horton

----- Original Message -----
From: "John Clement" <clement@hal-pc.org>
To: "'Forum for Physics Educators'" <phys-l@carnot.physics.buffalo.edu>
Sent: Monday, October 19, 2009 6:38 AM
Subject: Re: [Phys-l] DATA, FACTS, LAWS, THEORIES



> Sometimes they may be considered laws, but sometimes not.

Taking this in context, I believe what is intended by this sentence is
"Sometimes they may be considered accurate, but sometimes not." The
usage of "law" here would then be consistent with

> The term law would seem to imply that it is absolute,

But of course Hooke's law famously demonstrates that this is not
consistent with normal usage -- as John explicitly states.

My illustration of laws is to point out that the term has historically
been
used very inconsistently. But the one common thing in physics is that all
of our laws are relationships between variables. And one can not get a
relationship without having a number of data points. So saying there is a
relationship implies that it is a summary of data.

I think the statement that it is a relationship is extremely useful. When
you tell this to students it may take away the mystique that they have
built
up around the word law. This mystique has been actively taught by various
teachers and books that have told them that theories become laws after
being
proven or verified. At least in physics one can generalize the data/facts
without coming up with an equation, and such generalizations to my
knowledge
are not called laws.

As to the evolution argument, Evolution is a theory which provides
mechanisms for the archeological fact that there was change over time of
the
various species. One could call that archeological fact evolution, but I
think that being confrontational by calling Evolution a fact is not a
productive strategy. I have heard from teachers that students will often
accept the term change over time, while some will strongly object to
Evolution. Of course they have been indoctrinated to object to Evolution,
but since they don't really know what is, changing the terminology is a
good
end run around the problem. The author of the NYTimes article pointed out
that evolution is a historical fact, but Evolution is not necessarily a
scientific fact. The article informs the reader about what they might
like
in the book, and the author is obviously scientifically trained. One
might
disagree with the fact/theory concept the author uses, but it is
reasonable
and well within the mainstream of scientific thought.

John M. Clement
Houston, TX

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