View Full Version : Warning: Mistake in summary about work in cyclic motion

Paolo De Leva - Sport Biomechanics, Rome,italy
10-05-1995, 05:16 AM
Dear subscribers,

I realized that I misused a formula (W=DE) in my recent summary
about work in cyclic motion. Luckily, my stupid mistake had no effect
on the logic of the text, and on the conclusions, that I believe are
still valid (by the way that's the reason why I didn't spot the mistake
immediately). Only a few secondary statements were affected by the

I wrote that the formula W=DE means that the total work
is equal to the change in mechanical energy (kinetic+potential).
That's nonsense, of course. Even high school students know that
the total work is equal to the change in total (linear+rotational)
KINETIC energy, and not MECHANICAL energy. Potential energy has
nothing to do with total work.

Believe me, I am very very sorry, and sincerely apologize.

I am sure that many noticed my mistake. Unfortunately (for
you), nobody warned me, and I was not able to warn you before.
Luckily (for me) I was able to spot the mistake by myself.
[If you are curious to know how: I suddenly realized that my
description of the formula was uncorrect while I was trying to convince
a friend of mine that the total work done by a jumper is zero (see my
"tricky test for future biomechanics students", in the summary)].

I'll send you the revised version of my summary as soon as
possible. It is ready, but I prefer to ask one of you to review it, before
posting it to BIOMCH-L. Although I am sure that there are no other bugs,
I cannot risk again.
As soon as I am ready, I will also ask Ton van den Bogert
to substitute the new text for the old one, in the BIOMCH-L archive.


Paolo de Leva

P.S. I had tried to ask an opinion to Jesus Dapena about my summary
before sending it. Unfortunately, he answered that he didn't have the
time to review my draft in detail. He just browsed it (thanks again,
Jesus). Nevertheless, he managed to send me some very useful notes,
where he indicated some parts of my draft that were not well explained.
This helped me to make my text more easily understandable, but
unfortunately I didn't want to ask an opinion to someone else (I confess
I was sick about our exciting but time-consuming discussion).

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