I wrote this article for a Science Teacher's Publication
The internet abounds with some great (and not-so-great) java applet simulations available for physics teachers. My favorite locale is the widely acclaimed Colorado Physics site. In my pedagogy I have made use of about half the simulations available at Colorado but perhaps none with more success and gusto than Energy Skate Park (ESP).
ESP is specifically designed to demonstrate the key idea of Conservation of Energy (a central theme in both the Grade 11 and Grade 12 Physics courses – university and college) and in this regards it doesn’t disappoint. When entering the simulation one is presented with a parabolic roller coaster track. This track can be manipulated by the user to take on a somewhat diabolical appearance by the addition of extra tack or by the gerrymandering of the standing track into a variety of shapes….(loops, figures eights are all possibilities). Students love this.
A moving body, to be studied, can be selected from a number of alternatives (I am partial to the dog myself although many of the students liked the bug). The body is then released from a pre-determined height and bar and/or pie charts showing the transformation of potential energy into kinetic energy (and of course vice versa) with respect to time and position can be generated. For a more detailed analysis of motion the view of the system can be superimposed with a grid and the pause button can be utilized to better understand entity values at instantaneous points.
As an adjunct it is also possible to change the acceleration of gravity to mimic conditions on Jupiter, Earth and Space. The teacher can then ask the students to predict how the motion may vary in each of these cases and then test their hypothesis with the simulation. For an additional challenge one can vary the zero potential line as well to see how the relationships adjust.
Like all simulation lesson plans ESP works best with a worksheet that scaffolds the student through the learning process before allowing them to draw general conclusions about their observations. The worksheet is paramount and should have as its focus the elimination of key misconceptions. One such false belief is that if friction is added to the roller skate park then energy is not conserved. The ESP simulation allows one to model both the friction and non-friction case to show how thermal energy buildup is enhanced as the coefficient of friction is increased. The teacher could then use such feedback to make a distinction between the total energy available in the isolated system and that of the universe at large. Path length movement can also be related to thermal energy ‘loss’.
A further feature of this simulation is that it has a path locator feature that acts like a ticker tape attached to the skater. In working with college level students, in particular, I have found that this can act to supplement the students understanding of the influence of uniform acceleration on the displacement of an object.
Above all making use of ESP is a fun education positive exercise. I can vouch for that. My students thoroughly enjoyed it and I could see from evaluation feedbacks later on in the course that many of them had cemented the central idea of Conservation of Energy. This is a definite four star program that is well worth the effort of the lesson plan.
 See http://phet.colorado.edu/simulations/sims.php