A good example of an interactive web technology that brings added benefit is the set of small scriptable Java applets-we call them Physlets-being developed at Davidson College. Since Physlets are scriptable, the physics is usually be added by the HTML author. They are designed to be embedded into physics problems. They can be embedded directly into HTML documents and can interact with the user by employing a scripting language such as JavaScript. For example, the 75 kbyte Animator Physlet we have written is used to move a shape inside the applet's bounding box along a predefined path, [x(t), y(t)]. Adding this Physlet to an HTML page is no different than adding an image. Creating a 10-pixel diameter ball that follows a parabolic trajectory requires the following script:

Although animation can certainly be accomplished using more sophisticated programs such as Interactive Physics or possibly even quick time movies, two or thee lines of script connected to another problem can add additional shapes to the applet or change the trajectory into a sinusoidal oscillation. A VCR-like set of control buttons allows students to start, stop, and step the animation. The mouse can be used to read scaled coordinates. Presenting visual rather than textual representation of information necessary to do a problem changes the problem solving strategy. It also allows for different types of questions. What is the acceleration of the red ball? Are the laws of classical dynamics observed in the collision between the red and the blue balls? Which planet in the animation does not obey Kepler's laws? In problems such as these, the student must observe the motion and make appropriate measurements to obtain a solution. Physlet based problems-along with video based problems-are now being distributed as part of a web-based physics homework system at North Carolina State University. It is believed that video and animation can significantly influence students' visualization of some types of physics and that mastery of these types of problems could significantly improve their understanding of physics concepts.