The Traffic Accident Reconstruction Origin -ARnews-

Re: Snowmobile speed response to archive thread

Brian P. Griffin ([email protected])
Fri, 6 Nov 1998 17:52:44 -0500 (EST)

Dear Mr. Baxter,
Thank you for your patience; I hope you won't mind indulging
a few of my observations.
You recently wrote:
>Brian. Thanks for your response. I believe it has pointed out that our lack
>of communication in this thread has been related more to "semantics" than to
>"physics."
A layman might well use terms like "mass" and "weight" interchangeably, but
if I attempt to cry "semantics" at a physics exam, my answer will still be wrong.
The distinction (in physics) between "mass" and "weight" is somewhat analogous
to the difference between "inertia" and "momentum." I think it's important
for accident reconstructionists to be careful in their use of these kinds of terms.
You also wrote:
>you incorrectly used the term "rotational inertia"
>as a synonym for the "moment of inertia."
Boy, is my face red!! :)
This will come as quite a shock to the authors of my old undergraduate physics
textbook--Messrs. Halliday Resnick used "rotational inertia" quite liberally
as a synonym for "moment of inertia." In fact, I can think of at least one
widely-available dictionary of engineering terms that explicitly lists these
terms as synonyms. How do you plan to break the news to them ? :)
Maybe I can cover-up my "boo-boo" with a diversionary display of semantic hair-splitting:
(1)-inertia comes in several "flavors" (rotational, translational, relativistic)
(2)-there are several types of "moments of inertia":
(e.g. 1st 2nd area moments of inertia, 1st 2nd mass moments of inertia, polar moment of inertia etc.)
which are useful for finding things like center-of-mass or centroid of damage etc.
(3)-each type of "moment of inertia" can be taken about infinitely many axes.
SO---we were ALL WRONG!
We should all have written "the second mass moment of rotational inertia
taken about the pitch-, or y-axis." (You're not taking any of this seriously, I hope.)
Besides, I was only quoting Mr. Schmidt, BOTH of you said "rotational inertia" FIRST! ;)

Brian P. Griffin
[email protected]

NOTE: You are reading in an archived session of ARnews. It is possible that this topic is still being discussed. To see if this topic is still active, or of there were any more recent posts on this topic, check later archives of ARnews.

If there is no current post, and you would like to add to this topic, link to the Current ARnews Discussion and begin a new thread. Be sure that if you are starting a new post that the thread title does not contain the abbreviation RE: Placing RE: at the beginning of a new post will confuse Hypermail and prevent others from answering your post in the future.

For example, to continue this discussion look for a thread titled

Snowmobile speed response to archive thread

If this thread does not exist in the current archive, you can begin another one by using that title.