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Ai Phing Wrote:
[snip]
My students tend to think of g as the force. And I have to keep
correcting them that it's acceleration, not force. I use the words
"gravitationl pull" or "weight" for force though. I never thought of
gravity as a field. That really clears things up. (Understanding comes
really late in life....)
Be very careful how you use the language when talking about "g." Students
hve more trouble with this concept than almost anything else in mechanics.
Clearly "g" is not the force of gravity. That is "mg." But neither is "g"
an acceleration, and this is one of the problems that students have. "g" is
properly the strength of the local gravitational field (corrected for the
rotation of the earth), and it should not be confused with an acceleration.
The fact that a freely falling object (in a vacuum) near the earth's
surface falls with an acceleration numerically equal to "g" is due to the
fact that what we call "inertial mass" and "gravitational mass" appear to
be the same thing (this is the first step towards Eintein's general theory
of relativity), and so we can cancel the "m"-term out of the second law
equation mg=ma. I know that I am fighting a losing battle in trying to get
textbook to stop using the phrase "acceleration due to gravity" as the
definition of "g" but I think this is why so many students are confused on
this point (as I was at that stage as well).