Re: [Phys-l] definitions ... purely operational, or not

[Hugh Haskell <haskellh@verizon.net>]

At 13:28 -0700 11/09/2010, William Robertson wrote:

>  By the way, the folks at NASA and astronauts
> increasingly use the term "microgravity" in an effort to clear this up.

And that, IMO is the worst offense of all. That will surely convince 
the students that there is no gravity in space. Using that term 
clears nothing up, it only introduces new prejudices. Yes we can say 
that in free-fall the astronauts are in a gravity-free environment, 
in accord with general relativity, but that is a very subtle concept, 
and not one we should subject students to until after they have had 
some time to get the intuitive ideas straightened out.

Every student, and many teachers, especially new ones, bring a lot of 
improper baggage with them when they study physics, and it is 
important that we lead them gently but firmly to the ideas about the 
world that we know work and which will serve them well in the world 
they will end up living in. IMO teaching them that mg is weight is 
not one of them, in spite of the fact that many come to us thinking 
that way. I like to start off with g expressed in terms of newtons 
per kilogram, to de-emphasize the connection of g to acceleration. 
Once they understand g as the gravitational analog to E, and that it 
uses analogous units, then they are beginning to understand just what 
all those forces that they have been fooling around with are, and 
they might even be open to the idea that mass could just as easily 
have been called "gravitational charge," and that it can also be 
thought of in terms of inertia. Or more likely we would use the 
converse idea, that what we call charge can be looked up as 
"electrical mass." Now we can talk about inertial mass, and write the 
gravitational version of NSL as m(inertial)*a = m(gravitational*g, 
and the electrical analog as        m(inertial)*a = m(electric)*E. 
This enables us to show the students what I think is one of the 
greatmysteries of the world--that while the ratio of m(electric) to 
m(inerital) is a value that we can freely choose, the ratio of 
m(gravitational) to m(inertial) is always exactly 1. And we have no 
idea why that is true. (More properly, I have no idea why that is 
true, but there may be some esoteric explanations to be found in 
areas like string theory or the like that I have not been exposed to.)

Whether we want to go into all that is open to discussion, but I 
would argue most strongly that the word "microgravity," especially as 
used by NASA, should be banned from the English (and every other) 
language. I cringe every time I hear someone who damned well should 
know better  say it.

Hugh
--

Hugh Haskell
mailto:hugh@ieer.org
mailto:haskellh@verizon.net

It isn't easy being green.

		--Kermit Lagrenouille