Kinetic vs. Sound vs. Thermal

I want to talk about a small group discussion I observed during the 2nd day of the E1 workshop.  The entire discussion is about 15 minutes and the every second of it is awesome!  I'll focus on three short excerpts for this post.  If you want to check out the full discussion it runs from about 57:00 to about 1:11:00 on the E1 120807 1441 T2 video.

Context

Each group is trying to use energy cubes to tell the energy story of a ruler hitting a metal puck which then slides across the floor.  In the morning Lane did this as a demonstration and the teachers acted out the interaction using energy theater.  Group 2 has decided that the interaction involves kinetic energy, thermal energy, and sound energy.

Defining Energy Types

Mary (green stripes) and Sid (blond hair) have been debating for two or three minutes what object(s) should receive sound energy.  Mary has just agreed to move on when Julie (brown hair) interjects to re-frame Mary and Sid's discussion in a really awesome way.

Julie shifts the discussion from 'what objects have sound energy?' to 'when do we call it sound and when do we call it kinetic?'  Julie articulates this question beautifully and her question gives Mary and Sid some common ground to build from - they both agree the ruler and puck are vibrating after the collision.  Mary wants to call the energy associated with this vibration sound energy while Sid wants to call it kinetic energy.  Julie points out that they do not have a general criteria for differentiating between sound energy, kinetic energy, and heat energy.  Julie mentions "molecules moving in a certain way" as a criteria for defining sound energy but she is not satisfied by this criteria.  Sid proposes another possible criteria for sound: that sound energy can only exist in air because that's where we hear the sound.  Both of these are excellent attempts at defining a criteria for sound but neither is fully satisfying to the group.

I was confused during my first few viewings by Julie's comment about wanting the representation to be three-dimensional and Mary's ensuing gesture with the cube.  I think what they're saying is that they want to move an energy cube from the ruler to the air but they don't want this cube to have to pass through the puck because they don't know what to call that piece of energy when it is in the puck.  Lifting the cube off the whiteboard represents a really cool blending of the spatial representation on the board with the physical space in the room, but that's a topic for a different post.

Skip ahead one minute to the next clip:

Mary proposes having sound only in the floor and the air (presumably building off Sid's suggestion).  Julie at first says it has to be in the air but then backtracks and says "Well no it doesn't.  It could be through solid."  Julie seems to be saying that sound can travel through a solid.  Sid is unsure whether the energy should still be called sound while it is moving through the solid.  No one knows the answer to this question.  Julie suggests that "it's all of it all at once".  Julie's pseudo-answer is inconsistent with energy cubes in which each cube must be in a single location and showing a single face (energy type) at each moment in time.  I'm really loving how the activity/representation of energy cubes forces the group to not accept an incomplete answer to what really is a fantastic and difficult question.

Energy States vs. Energy Types

Skip ahead another minute to the last clip.  Adam has been listening for a little over two minutes but this is the first time he speaks.

Julie proposes a third possible criteria for differentiating different types of energy: the speed of the vibration.  I'm so blown away at how they keep trying different, totally legitimate criteria for differentiating types of energy.  Sid goes a different route and wants to promote 'kinetic' to being an 'energy state'.  Then sound could be a type of kinetic energy and they would no longer need to pick between kinetic energy and sound energy.  I wish Sid would have ran with this idea.  I would have liked to see what she did when the time came to differentiate between sound energy and thermal energy.

In the end they never resolve their question.  They realized that the demo as Lane did it had the puck and the ruler in contact from the beginning (rather than the ruler striking the puck).  They decided to represent the ruler and the puck as a single object on the diagram.  This allowed them to move an energy cube from the ruler/puck directly to the air, at which point the energy became sound energy.