For a logical treatment of motion in a circle go to "Physics Education",
volume 33 number (6) November 1998 pages 359 to 365 (available on
Institute of Physics website)

Steve Bolter
Wickham House
Gestingthorpe
UK - CO9 3BH


-----Original Message-----
From: learning-science-concepts@...
[mailto:learning-science-concepts@...] On Behalf Of Dileep
V. Sathe
Sent: Thursday 01 June 2006 23:42
To: learning-science-concepts@...
Subject: LSC: Direction of Circular Motion

On the Direction of Circular Motion

Dileep V. Sathe
2 Prerana Apts, A-40, Kasturba Society, Dighi Post, Pune, MH, 411015,
INDIA
Email: DileepSathe@... Phone: [020] 2669-6965

Following question has been included in some question papers of coaching
classes, training HSC students specially various CETs. For example, see
MHT-CET 2006 paper of the Vijeta Academy, Kolhapur, Sakaal 15th April
2006, page 13.

A body is revolving with a constant speed along a circle. If its
direction of motion is reversed but the speed remains the same, then, A]
The centripetal force will not suffer change in the magnitude, B] The
centripetal force will have its direction reversed, C] The centripetal
force will not suffer any change in direction and D] The centripetal
force would be doubtful. The correct answer, as given by the Head of
Academy, is A.

Coincidently, this question is concerned with a global and chronic
problem in physics education - that is the global tendency among
students of choosing the forward force as resultant force, acting on a
body in uniform circular motion, and ignoring the centripetal force. My
25-year long research is concerned with the same and therefore I would
like to draw attention of all science teachers, not only physics
teachers, to some key issues.

I have shown that the present treatment of circular motion is not
logically perfect and conflicts with other concepts like that of work
and the law of parallelogram. Albert Einstein's GR originates in the
logical incompleteness of Newton's laws of motion. But, my work shows
that that logical incompleteness has not been completely understood - as
yet - and therefore we are still facing grave problems in teaching /
learning Newton's laws of motion, although they are known for 300 years.
Due to this conflict a large number of students tend to give the wrong
answer. Since this answer is wrong, as per teachers, the conflict
between teachers and students latently drives students away from
physics. In fact, this tendency has grown to such an extent in recent
years and there it was essential to declare 2005 as the Albert Einstein
year for the sake of popularization of physics.

The problem of direction has hardly received due attention of
educationists and physicists in the past because the reversal of
direction of motion is never considered in the teaching of uniform
circular motion and therefore the above problem will be provocative.
This why I have been discussing my work with physicists, rather than
educators. For more information, see the text of my lecture, which was
dedicated to the memory of Prof Abdus Salam in a symposium in samarkand,
UZBEKISTAN, August 1999 -
http://www.iupac.org/publications/cei/vol2/0201x0026.html

Finally, I would like to narrate my own experience of 16th January 1993
in a symposium in N Wadia College, Pune, I asked the audience to make a
trajectory of the body on which a centripetal force was acting. It was
taken from the PSSC Physics, 7th Edition, 1991, Kendall-Hunt Publishing
Co, USA. And, as per my expectation, some young people [all MSc,
Physics] drew anticlockwise trajectory and some did the opposite. This
was quite useful for me why the comprehension of circular motion is
still in global trouble - though it is known for more than 300 years.

So, I request all science teachers, past and present HSC students to
consider this problem earnestly and send their views to me - on options
given in the questions and on any relevant aspect of circular motion and
other related topics like the planetary motion and Bohr's theory of
hydrogen atom.

---------------------The
End--------------------------




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