Using Java Applets for Inquiry-Based Physics Lessons

Science teachers and students enjoy hands-on laboratory investigations. It gives students a chance to play with some nifty gadgets and gives the teacher the opportunity to assess students' research and teamwork skills. Students also get a taste of what science is like in the real world. 

Unfortunately, such activities can also be very time-consuming, and the cognitive payoff is not always worth the extra time. Data collection requires precision measurements and equipment that teachers do not always have access to. Furthermore, the data collected may not reinforce the content teachers are trying to cover. To be sure, there is some value in students asking why the data does not seem to confirm the theory. It makes them more sensitive to sources of error. However, at the high school level, it is arguably more important that students come to understand fundamental concepts. To that end, they need to perform investigations that successfully illustrate those concepts.

Fortunately, today's technology allows teachers and students to have the best of both worlds. There are several sources of high quality Java Applets that simulate various physics situations. They allow students to manipulate various parameters so that they can observe the effect of those changes. In this article I summarize a recent investigation I conducted on the concept of momentum and elastic collisions, showing how to use such applets to achieve important educational goals. (The applet I used, Elastic and Inelastic Collision, came from Walter Fendt's website, Java Applets on Physics).

This applet simulates the collision between two wagons. Wagon 1 (W1) moves towards Wagon 2 (W2), which can either be at rest or moving itself. The applet can simulate either collisions that are either elastic (the wagons bounce off each other) or inelastic (wagons stick together after colliding). It allows students to manipulate the wagons' masses, and the speeds of the two wagons before colliding.

In a physics class it is important that students have the opportunity to predict the outcome of various events, based on their intuition and their knowledge of physics concepts. Such predictions not only allow the teacher to weed out misconceptions, but give students practice thinking about physics situations. The first situation I presented involved an elastic collision, in which W1 moved toward W2, which was stationary, at a certain speed. Both wagons were set to the same mass. I asked students to write down their predictions. Most predicted that W1 would set W2 in motion and keep moving itself, perhaps at a slower speed. What actually happens, of course, due to the laws of conservation of energy and momentum is that W1 transfers all its momentum to W2. Therefore, W1 was observed to come to a complete stop, and W2 moved off with the same speed W1 had before the collision.

Next, I asked them what would happen if the mass of W2 was decreased. Beginning to catch on, most students realized that this was when what they originally predicted would happen; W1 would set W2 in motion, but it would still have some momentum left over, and so would keep moving at a much slower speed than it started with. This is indeed exactly what students observed.

The next question was what would happen if the mass of W2 was increased. This outcome was harder to predict. Not many students realized that W1 would bounce back with a smaller speed (in the opposite direction), while W2 would start moving with a small speed in the original direction. Still, once they observed it happen, they were able to successfully explain this outcome using the conservation laws. 

Finally, students were able to summarize their findings in terms of the conservation laws. They also realized that to correctly predict all outcomes, both conservation laws are required. 

I was very pleased with the results of this investigation. Students were able to engage in the twin activities of prediction and explanation, which I regard as the most important in any science course. The students did not waste time making potentially inaccurate measurements of the wagons' speeds before and after the collision, and they did not come up against the obstacle of less than perfectly elastic springs in the wagons. Again, there is some value in students' thinking about potential limitations in measurement, but teachers usually have to make trade-offs, and I regarded increased conceptual understanding as more important.