In the lecture of Wed 2/22 we did a problem of a person
stretching a perfect spring by pulling a mass at the end
of the spring at constant speed. In this example, I did
a very bad job of explaining why the force exerted by the
person is equal in magnitude and opposite in direction to
the force exerted by the spring. Here is a correct
explanation. This is also available as a pdf file
and at the Noble Library Copy Center. I apologize for any
confusion this might have caused. GBA.