Chronology Current Month Current Thread Current Date
[Year List] [Month List (current year)] [Date Index] [Thread Index] [Thread Prev] [Thread Next] [Date Prev] [Date Next]

Re: [Phys-l] "Unlearning"



On September 19, 2010 at 3:34:07 PM, John Denker wrote in part:

Regarding unlearning, in the sense of cancellation, here are some examples:

*) The textbook says by way of definition that «An object in
mechanical equilibrium is stable....» Unlearning is when you
find out that mechanical equilibrium does /not/ imply stability.

*) The textbook says «Most of the cannonball’s momentum is in
speed; most of the recoiling cannon’s momentum is in mass.»
Unlearning is when you find out that momentum is never "in"
mass or "in" speed ... and even if it were, it is a proverbially
bad idea to compare apples to oranges.

*) The textbook says «The Rule For Toppling. If the center of
gravity of an object is above the area of support, the object
will remain upright.» That statement appears directly underneath
the picture of a tall, narrow, double-decker bus. Unlearning
is when you discover that keeping the center of gravity above
the area of support is absolutely not sufficient to prevent
toppling under foreseeable operating conditions.

*) The textbook says «We say that an object balanced so that
any displacement lowers its center of mass is in unstable
equilibrium.» Unlearning is when you find out that's just
not true.

*) The textbook says «The equation E=mc^2 is more than a formula
for the conversion of rest mass into other kinds of energy, or
vice versa. It states that energy and mass are the SAME THING.»
Unlearning is when you figure out that mass and energy are not
the same thing.

Etc.
My suggestion regarding the "unlearning" was only about concepts and theories
that had been proven useful and correct within the domains of their
applicability.
They will remain useful and correct within these domains (which themselves
depend on the required accuracy). Classical Mechanics with F=ma and P=mv is
still taught in colleges and remains, quite fairly, a necessary pre-requisite
for courses of EM, QM, SR, etc. So I don't see much to unlearn here.
But of course, my suggestion was not intended for cases of wrong statements
which must, indeed, be unlearned or corrected. In this respect, there is no
argument against unlearning in the quoted examples by J.D., except, possible,
the second one. To me, the second example is just a nice way to illustrate that
a slow-moving but massive object may carry the same amount of momentum as a
fast-moving but light object.

Moses Fayngold,
NJIT



Forum for Physics Educators
Phys-l@carnot.physics.buffalo.edu
https://carnot.physics.buffalo.edu/mailman/listinfo/phys-l