I was presenting a lesson on engaging starts for my preservice elementary science methods class, and I did the lycopodium flash to model an engagement on surface-area to volume ratio. Lyndon Brooks emailed me this video of the demonstration that he shot with his cell phone. This is my first reception of a video of a class I am teaching. Rillero Lycopodium Flashmov.mp4

This week I was at Santa Clara Unified School District visiting Kathie Kanavel,  Coordinator for Educational Technology. Kathie told me about her math teachers using their Lumens document cameras to record their lessons, with audio, and then they post them to YouTube. What a great way for students to review the lessons. Parents who are trying to help can also experience the lesson.

Adaptive Curriculum has a different way of engaging students in a lesson on surface-area to volume ratio. They use the discrepant event of cheese cubes in a microwave. Most of us, because of conventional oven experiences, would think that the smaller cubes would melt first. But with a microwave oven, the cheese heats from the inside and the larger cube, because it has a smaller surface-area to volume ratio, retains heat better and it melts first.

Whether at the high school or middle school level, students studying graphs of motion are often confused. One area of confusion occurs in the difference between distance-time graphs and displacement-time graphs. Virtual activities can cause more confusion, unless the right ones are chosen.

Distance-time graphs are a part of many middle school math and science curricula. A Google search for “distance-time graphs” reveals about 10,500 websites with many Java-based and Flash-based online activities. The problem for physics learners and teachers is that in many cases, the developers call their graph a distance-time graph but in reality they are displacement-time graphs.

Here are some examples of (otherwise) good websites making this error:

Moving Man 

Football (soccer) Distance Time Graph

GCSE Bitesize 

There are a few good sites that accurately portray distance-time graphs.

“Crocodile-clips” is a simple, free site where students move a helicopter and create a real-time distance-time graph. It doesn’t matter if the helicopter is moved away from or closer to the starting point. The true distance traveled is displayed on the graph. It is simple but effective.

Commonwealth Curriculum Pack (CCP) is a more involved site. I used this with my mixed age physics class last week and it made the point and kept their interest.

This site uses the context of the 100-meter race to show different arrival speeds. Quickly, my students learned that the steeper the slope (gradient), the greater the speed of the runner. Then we viewed several nice animated sequences of interpolation, which they then interpreted.

PBS Teacher Line http://www.pbs.org/teacherline/resources/activities/race/readings/race.htm.

Students observe stick figures run 400-meter races. They can see the runners move at actual speeds or average speeds, so this serves as a good way to help students understand instantaneous speed versus average speed.

Motion graphs will probably always be confusing for some students. We can reduce confusion with distance-time and displacement-time graphs by using internet resources that accurately portray the difference.

Additional Resources

Adaptive Curriculum’s Activity Object: “Truck On: Position and Velocity-Time Graphs” 

The Physics Classroom Tutorial: Distance and Displacement