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Re: "Simple pendulum"

Hi Ludwik-
You asked, why isn't my misconception true?
Then you remarked:
***********************************************
Every misconception can be ridiculed by those who
know better. But it REALLY WAS my misconception.
Where did it come from? Probably from knowing
that, mathematically, a circular motion with constant
speed is a superposition of harmonic oscillations along
the x and y axes. The equality of amplitudes and the
phase difference of 90 or 270 degrees always leads to
circular motion.

Are you opposing the idea of collecting misconceptions,
Jack? I mean misconceptions some of us had, and also
those we identify in minds of students. No, I am not
referring to misconceptions such as "cows must drink
a white fluid to produce white milk."
**********************************
I don't understand the generic question, "
Why isn't my misconception true?
I do understand the following generic question,
"I believe A because it seems to follow from B, C and D;
is my reasoning correct." I think that my example was
apt.

***************************************************
Jack also commented on the idea that

the concept of perpendicularity does not apply
to curved lines.

He wrote:

Say what? Lines of latitude and lines of longitude
on a sphere are curved and respectively perpendicular
to each other.

Only very short segments near the intersection points
are nearly perpendicular. In my terms if a line A is
perpendicular to a line B then any segment of A must
be perpendicular to any segment of B (in old geometry).
I would say that "planes of latitude" and "meridian planes"
are perpendicular, but the lines you are referring to are not.
What is wrong with this position?
***********************
Maybe nothing. What is your definition of perpendicular?
My definition of perpendicular is purely local at a point of
intersection.
Regards,
Jack


"I scored the next great triumph for science myself,
to wit, how the milk gets into the cow. Both of us
had marveled over that mystery a long time. We had
followed the cows around for years - that is, in the
daytime - but had never caught them drinking fluid of
that color."
Mark Twain, Extract from Eve's
Autobiography