Re: Conservation of ME and nonconservative forces

[Herbert H Gottlieb <herbgottlieb@JUNO.COM>]

On Tue, 26 Jun 2001 18:56:40 -0500 "lorinda.stinnett"
<stinn001@BAMA.UA.EDU> writes:
> On Tue, 26 Jun 2001, QUIST, OREN wrote:
>
> > Friction does no work in this case because there is no slipping.
> That is,  there is a force but no displacement of the contact point.
> I agree with you.  My problem is that the displacement defined in work
was not limited
> to the  point of contact.  For instance: If a box is pushed across the
floor
> is  the work done only to the part of the box that is in contact with
> the hand  pushing it, or is the work done on the entire box?

1. I believe that friction is doing some work in this case regardless of
whether or not
the rolling ball is slipping.  It is called rotary friction rather than
sliding
friction and it eventually causes a ball rolling along a horizontal
surface to
slow down and eventually stop moving.

2. If a box is pushed across a floor, work is done on the entire box.
Otherwise
only the bottom of the box would eventually stop moving while the rest of
the
box continues moving along on its merry way.

Herb Gottlieb from New York City
(Where boxes pushed across a floor tend to to scratch the box as well as
the floor)