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Re: [Phys-L] two very different "gravity" concepts



The big conceptual problem is making F_g = m g where g=9.8m/s^2 rather than
g=9.8 N/kg. This is known from the research into student learning. Of
course then when the "universal" law is introduced they need to use a
"refined" model for gravitation. Gravitation is a much better word than
gravity because gravity is usually used as a noun. So students then use it
as the source of the force rather than thinking about an interaction.

John M. Clement
Houston, TX


The conceptual problem seems to result from the term "zeroing
out." When we say that g in a given location, is 9.8 m/s^2,
we refer to what is measured in an elevator at rest with
respect to the center of our planet (or outside of that
elevator). It is the g calculated from the universal
gravitational force, either in Spain or in N.Z.

What might be measured in a falling elevator is called
apparent acceleration. And we know how it is connected to 9.8
m/s^2. I do not remember students being confused, especially
when the rotation of the earth is neglected.

What else am I missing?