Energy Theater: Where is the thermal energy?

On Thursday afternoon (8/8/13) in E1, the class enacted its second energy theater; this time for the mousetrap car.  In this pair of video episodes, I am showing a group that was formed by taking 2 members from each of the four tables (in Noah’s ark style?).  These clips focus on their attempts at determining where the thermal energy will be present.

In the first episode, Tanya (white blouse) is the lead voice.  “Yeah, let’s ignore the air,” is her big remark at 0:18, with immediate agreement from Maggie.  “Air is minimal, we don’t have to put it into the equation.”  The group seems to be in agreement without needing further clarification.  “It’s like a frictionless track,” she adds.  Again, the group seems okay with this, but Lane interjects, “hold on.”  As Lane attempts to draw out a more detailed description, Tanya adds more and says “it’s minimal and it won’t change a variable between our experiments and it would be very small compared to what we’re doing.”  At the end she brushes it aside with a sweep of the arm, “let’s eliminate one thing.”  Again, the group is happy; except for Jeff (blue shirt).  A long “eeeehhhh,” escapes his lips.  But at this point, they are moving on.

For the next three minutes, they discuss how to demonstrate elastic energy and how to show elastic transforming into kinetic and how that transfers from the “drive train” to the body of the car.  This video picks up as Tanya shows herself as changing from elastic to kinetic, moving to the body of the car, and then at 0:20 says “since I’m scraping against the floor, I’m done.  I’m heat.”  Finally, Jeff speaks up: “I’m going to disagree.  I think there’s a fundamental difference between the car and the hockey puck.  We have static friction and not…”  At that moment, Tanya gives a little gasp.  Jeff goes on to say “I think wind resistance is going to stop this car more than friction.” 

“But if we don’t have friction, how will it move forward?” Tanya asks.  She’s not convinced.  Jeff goes on to describe how he thinks its static friction with the floor that results in rolling and that no heat would be generated.  He ends his explanation with a satisfied clap of his hands at 1:12.  Other members of the group chime in and start asking questions, looking for further clarification.  At 1:34, Tanya begins looking around.  She goes and finds the spare rope not in use and sets it up as the air; she’s bought into the idea.

** Video should be here.  I'm having problems with errors.  

Go to folder 2013 E1 Episodes and watch "E1 130808 I think its the Air"**

I think this pair of episodes shows the power of Energy Theater.  If a group is willing to engage in open dialog, then members have a safe place to share their ideas.  Tanya made some great arguments, but there was room for Jeff to speak up as well and present what a more accurate representation. 

These episodes also represent an evolution in thinking as one moves from the idea of sliding friction to rolling.  Sliding friction is the easiest way to think of friction, and this naturally leads people to the conclusion that the floor receives the largest thermal energy piece.  But a more advanced representation demands looking at rolling and the physics at play between the ground and the tires.  Also, the possible friction in the axles was mentioned.  It was interesting to see these teachers navigate the ever expanding complexity of the problem, recognizing different components that might lead to thermal energy.  While a 100% “correct” answer is not possibly, an appreciation for the complexity is apparent.

Full video: E1 130808 1257 T7&outside-1