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Re: Free Body Diagram - changes of changes



The problem of understanding the relationship of acceleration to
velocity is not an isolated problem. Economics professors will tell you
that students have a terrible time understanding the difference between
the inflation rate and the rate of change of the inflation rate. There
have been many instances of US presidents and US economic advisors
getting this goofed up during press conferences; I have witnessed a few
of these myself.

I have seen politicians try to talk about the change in the change of
the change of the cost of living. Suppose we had inflation of the
consumer price index of 4.00% for last year. Suppose the inflation this
year looks like it is going to be 4.40%, so it looks like it is going to
be 10% higher this year than last year. But wait... two years ago
inflation was 3.48%, so from two years ago to last year the rate of
increase of inflation was 15%. So, the politician is trying to explain
that the change of the change of the change in the cost of living has
decreased 5% from being 15% two years ago to being 10% this past year,
therefore the economic policies are working so please re-elect me. Even
if the politician understands this, the public doesn't understand it.
The politician is saying that something about inflation went down by 5%
yet things cost more this year than they did last year. The public
says, "Good grief, why can't we get a straight story."

Also note that I have used typical language above, yet the language is
confusing because percent is not always being used the same way. The
increase from 4.00% to 4.40% is a 10% increase, but the drop from 15% to
10% is a 33% drop not a 5% drop. This stuff would be hard to understand
even if we use plain numbers; the percentage business makes it even
worse. What a mess.

Michael D. Edmiston, Ph.D.
Professor of Chemistry and Physics
Bluffton College
Bluffton, OH 45817
(419)-358-3270
edmiston@bluffton.edu

This posting is the position of the writer, not that of SUNY-BSC, NAU or the AAPT.