inertial frame

[JohnDenker]

See item #107 for a catalog of related issues.

In section 12.1 on page 259 it says:

Avoid analyzing forces from a rotating frame of reference because such a frame is accelerating and therefore noninertial.

If you want to say that rotating reference frames are beyond the scope of the course, that's 100% OK.

However, you can't explain that by complaining that such frames are non-inertial. According to any modern (post-1915) understanding of physics, and according to what it says in chapter 13, the terrestrial lab frame is an accelerated frame ... but we do not "avoid" it. We rely on it very, very heavily.

The fact is, the methods for handing a rotationally accelerated frame are _more complicated_ than for a straight-line accelerated frame, but the methods do exist. They are quite well known. Students (like everybody else) have plenty of experience using rotating reference frames, for instance when a car makes a tight turn. They may not know how to analyze such things super-quantitatively, but they know such things exist.

[ericmazur]

I agree... but... do you have any suggestions on how to fix this?

[JohnDenker]

As usual, my solution is very direct. Here's how I say it:

• The centrifugal field exists in the rotating frame and not otherwise. It does _not_ depend on the motion of this-or-that object.
• The centrifugal field is as "real" as the gravitational field (g). In fact, the two are intimately related. Both exist if-and-only-if we choose an accelerated reference frame.
• For the moment, the centrifugal field is beyond the scope of the course. Even in situations where it might make sense to analyze things using a rotating frame, we will keep things simple by choosing a non-rotating frame.