From: "JACK L. URETSKY (C) 1996; HEP DIV., ARGONNE NATIONAL LAB, ARGONNE, IL 60439" <JLU@hep.anl.gov>
Date: Sun, 7 Dec 1997 13:54:10 -0600
Hi all-
Dick Hake writes, in part, on the subject of inertia:
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In =93A Guide to Introductory Physics Teaching,=94 Arons suggests that
introductory-course students might be lead to a satisfactory
understanding of F and m in Newton=92s Second Law F =3D ma, by considerin=
g a
=93Newtonian sequence=94 thought experiment in which a force scale is
calibrated in terms of the extension of a spring attached to a standard
body which undergoes various constant accelerations on a horizontal
runway. The inertial mass m of any body is then operationally defined
in terms of the ratio F/a. That experiment has been actualized as a
student Socratic Dialogue Inducing (SDI)laboratory (2,3) using a force
probe, sonic motion detector, computer tools, and software developed at
Tufts University and utilized in =93Tools for Scientific Thinking.=94 (4)=
=20
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A somewhat related approach, that I have used, is to attach
masses to a horizontal spring with the mass sliding on a smooth surface.
We observe, empirically, that a mass-spring system oscillates when displaced
from equilibrium. We also observe that "heavy" masses oscillate more slowly
than light masses. Our operational definition of "the inertia of a mass"
is to measure the period of oscillation of the mass when it is attached
to THE INTERNATIONAL STANDARD SPRING which is kept at constant temperature,
pressure and humidity in a government building in Pella, Iowa. Using this
definition, mass (inertia) would be measured in seconds.
The advantage of this definition is that the teacher can keep
referring back to it whenever the subject of inertia arises and can
quickly reconstruct the demo for the (almost certainly) forgetful students.
Regards.
Jack