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# [Phys-L] centrifugal field; was relativistic acceleration....

• From: John Denker <jsd@av8n.com>
• Date: Mon, 10 Nov 2014 08:17:55 -0700

On 11/10/2014 07:44 AM, Bob Sciamanda wrote:
Perhaps it should be noted that to an observer at rest in frame B the
travelling clocks were "always" out of synchronization - even when
they began their trips, at rest in frame A.

Yes.

------------------------

A lot of what's going on with the accelerating rocket can
be understood in analogy to the plain old centrifugal field.
If you use an accelerated reference frame, peculiar things are
going to happen. This applies to straight-line acceleration as
well as circular acceleration. Much of it applies to classical
(low-speed) acceleration as well as relativistic acceleration.

Here's a suggestion for how to handle this in the introductory
course:

1) It helps to say that that the centrifugal field exists
in the rotating frame and not otherwise. It doesn't matter
whether this-or-that object is rotating; what matters is
whether the frame is rotating.

2a) If you want to say that rotating frames (and other accelerated
frames) are outside the scope of the course, that's 100% fine
with me. If you pick one particular inertial frame and stick
with it, a lot of complexity goes away.

2b) HOWEVER please do not tell students that rotating frames
do not exist. Do not tell them that the centrifugal field
does not exist. The centrifugal field is just as real as the
gravitational field -- no less, no more.

To repeat: It's OK to say it's beyond the scope of the course.
It's not OK to say it doesn't exist. As soon as you leave the
cosseted world of the introductory physics course, there are
lots of good reasons why somebody might want to use an accelerated
reference frame for some purposes.

As H.E. Fosdick put it: Persons saying it cannot be done are
liable to be interrupted by persons doing it.

You have to say "something" about it, because the topic is
guaranteed to come up. Students /know/ the centrifugal field
exists; they experience it every time they ride in a car. If
you say it does not exist, you just lose credibility. Forcing
students to "learn" stuff that cannot possibly be true is the
opposite and the enemy of critical reasoning.