Re: positive and negative work

[Gene Mosca <mosca@USNA.EDU>]

I agree with John Denker that the leg muscles do negative work.  If a muscle
contracts under tension it does positive work, if it lengthens it does
negative work.  The muscles in the front of the thigh are under tension and
lengthen as you sit.


On 11/8/01 8:42 AM, "Justin Parke" <FIZIX29@AOL.COM> wrote:

> A conceptual question from the fifth edition of Serway and Faughn College
> physics  (ch. 5 number 2):
>
> "Discuss whether any work is being done by each of the following agents and,
> if so, whether the work is positive or negative:
>
> d)  the leg muscles of a person in the act of sitting down."
>
> I say the muscles are doing negative work since they exert an upward force (to
> prevent the person from simply falling into the chair) while the motion of the
> person is down.  The answer in the book is positive, with no explanation
> given.
>
> Could someone explain this for me?
>
> Justin Parke

--
Eugene P. Mosca
Physics Department
MI350-B
United States Naval Academy
(410) 293-6668