Re: [Phys-l] Centrifugal redux

[John Denker <jsd@av8n.com>]

On 03/17/2009 05:07 PM, LaMontagne, Bob wrote:
> But if the forces are balanced I should be going in a straight line
> at constant speed.

The forces are balanced in the rotating frame.  The assertion that
balance of forces implies straight-line motion comes from Newton's
laws.  Newton's laws (in their usual form) do not apply in a rotating
reference frame.

> I'm turning because I have a horizontal component of lift
> perpendicular to my motion.

That's true in the non-rotating frame.

You are free to choose whatever reference frame you wish ...
but you must respect the right of others to choose differently.

Student pilots who have never taken physics are capable of
understanding the explanation using centrifugal forces in the
rotating frame.  After all, the pilot is attached to that
frame.  It is a disgrace to physics education that students
who _have_ taken introductory physics would be _less_ able to
understand this concept.

> Sorry - I am not a convert to the idea of "centrifugal force". 

Conversion is not the issue.  This is not a religious sect.

The centrifugal field is as real as the gravitational field.
  http://www.av8n.com/how/htm/motion.html#sec-centrifuge

The centrifugal field exists if and only if you are using a
rotating reference frame.

I don't have a problem if the introductory physics teacher says
that rotating frames are _outside the scope of the course_ ...
but "outside the scope" is not the same as "nonexistent".  The
teacher is allowed to choose the scope, but is not allowed to 
change the facts.

Anyone who has mastered the subject should be able to analyze
the situation either way (rotating and non-rotating reference
frames).

     Person saying it cannot be done is liable
     to be interrupted by persons doing it.
                    -- Harry Emerson Fosdick