For any of you who are interested in Web-based conceptual homework,
there is (finally) a new release of Physics Illuminations. (I've been
rewriting them to use the Open Source Library of Wolfgang Christian, et
al.). Note that because I retired from UNO in May, the web address has
changed. The new Physics Illuminations site is at
www.rlgreene.org/illum.html
(The www. is optional.) You can find the address for downloading on
that page. The new release has all but 3 of the old illuminations
(which I'm still working on) plus a new one dealing with conservation of
energy, using bar charts.