Re: [Phys-l] "Unlearning"

[John Denker <jsd@av8n.com>]

On 09/19/2010 10:55 AM, Moses Fayngold wrote in part:

>   In most cases, the appearance of a new 
> physical theory does not cancel the previous one.

[many examples snipped]

>   I would suggest to discard the term "unlearning" as totally misleading and 
> giving downright wrong picture of scientific progress.

This thread arose in the context of pedagogy, which is not
the same as the history of "scientific progress".

I think we all realize that we are talking about a complex
subject, and a one-word label such as "unlearning" is not 
-- and was never intended to be -- a complete, nuanced 
elucidation.  Buzzwords, almost by definition, are not
self-explanatory.

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 there are «two sets of ocean tides per 
day – two high tides and two low tides» as if that were an
inescapable consequence of the laws of physics.  Unlearning 
is when you find out that in most of the Gulf of Mexico the 
tides are diurnal: one high tide and one low tide per day.

*) 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.

*) The textbook says Bernoulli’s principle is «a consequence 
of the conservation of energy».  Unlearning is when you find
out that Bernoulli's principle is not a consequence of the law
of conservation of energy, not even approximately.

*) The textbook says «the kinetic energy of the atoms approaches 
zero, and the temperature of the substance approaches a lower 
limit. This limit is the absolute zero of temperature.»
Unlearning is when you find out that the kinetic energy does
not go to zero as the temperature goes to zero.

*) The textbook says «Blow warm air onto your hand from your 
wide-open mouth. Now reduce the opening between your lips so 
that the air expands as you blow. Adiabatic expansion – the 
air is cooled.»  Unlearning is when you find out that no part
of that explanation is correct.

*) The textbook says «Entropy is the measure of the amount 
of disorder in a system.»  Unlearning is when you find out
that that's not true.

*) The textbook says you can touch a high-voltage power line,
and «So long as you touch nothing else, you will receive no 
shock at all.»  Unlearning is when you find out that's not
true in principle and not true in practice.
 http://www.youtube.com/watch?v=rkYq17gTCq8

Et cetera.