As many of my readers know, starting in the late '90s, many clever, creative people around the world wrote cute (and sometimes very sophisticated) Java applets to demonstrate certain physics and engineering concepts. Examples include this great site by the University of Buffalo, a virtual lab by the University of Oregon, this resource by UCLA, this outstanding site from the University of Barcelona, etc. Many of us owe a real debt of gratitude for these resources, as they have been great educational tools.
A problem has arisen, however. You will notice that none of the applets linked above actually run. Because of security concerns about Java, the latest versions of Java require applets to have been compiled, authenticated, and certified (via electronic security certificates), or the applets simply won't be run by the virtual machine. For actively maintained sites (such as the excellent "physlet" effort from Davidson), the authors and maintainers have thoughtfully recompiled and updated their code. Others (the University of Colorado) have rewritten everything (!) in Flash or HTML5. Unfortunately, these are the exceptions, and many other cool sites are orphaned, with clever code that can't be run.
If anyone knows a work-around (some kind of emulator that would run the code in a walled-off way?), please describe it in the comments. It would be a real shame if the accumulated excellence of all those older sites was wiped out. Thanks.