The Micro: Analogies for Dropping the Ball

Context
Akbar has just joined the class in the middle of Day 2. His new group has explained that they saw a video of a bowling ball dropping and are trying to make an energy diagram and label the mechanisms. The group explains the diagram to Akbar. They are trying to describe and explain the interaction between the ball and the ground, and the resulting bounce. Don says he doesn't know how to show the bounce-back, but the group proceeds to do just that, using several interesting analogies.

Interesting Features
Three different vivid analogies are used to describe the encounter between the ball and ground.

1. "This would be compressing the molecules or something like a spring--like each little molecule would be like a little spring and it would come down and shoot it off." --Don
2. "I guess it's sort of like when you clap your hands you can feel it in both hands so you've got the same amount of feeling in both hands as they clap together" --Jean
3. "It's like a car hitting a brick wall, they're both gonna feel the same impact, right?" --Jean

After these three metaphors are rattled off in quick succession, Akbar says "And so the ground is moving?" This makes me think that these analogies (maybe in particular Jean's) have helped him understand that the ball has an impact on the ground even if it is not as obvious as the ground's impact on the ball.

Another feature that is interesting to me is Don's comment that "we're not even getting into the micro, what's really happening in there". I have noticed this too, that there is not a lot of discussion about movement of molecules. At another point in the class, I heard Rachel say to a group that you could also do "particle theater" about all of these scenarios, but that it would look different than the energy theater. I find myself very curious about the relationship between the two--I think I may still be confusing, for example, the movement of particles with kinetic energy itself. Jean goes on to talk to Akbar about how she had to explain to her students that while the molecules within an object might be moving, the object itself might not. This is especially interesting because (I believe) later in the same class, Jean stated that she felt that she did not understand what was meant by "bulk movement". In this clip it seems to me that she is describing exactly that concept.

Transcript
[00:00:00.00]Akbar: Now here, this kinetic to thermal is...
[00:00:04.21] Jean: From the air.
[00:00:06.10]Akbar: The air moving?
[00:00:08.27]Jean: The ball moving against the outside air, so that
[00:00:12.01] Akbar: Causing air to move
[00:00:18.01]So this kinetic here would be the air moving
[00:00:26.15]Melanie: So how would you like to represent the ground push-back to the ball?
[00:00:31.09]Don: Just the heat part? You would just put a K and then a T.
[00:00:42.00]Akbar: So kinda reverberation, like *unh*?
[00:00:47.01]Don: Actually the bowling ball bounced, and it hit the ground and it bounced back up
[00:00:52.09]but we didn't--we're not worried about the bounce-back.
[00:01:03.06] -Melanie: Then after it's in the...
-Don: I'm not even sure how you would show the bounce-back.
[00:01:08.00]-What would be going on to make that ball go back up
-Jean: Well it would just happen again
[00:01:12.03]only less and less
[00:01:15.15]Don: This would be compressing the molecules or something
[00:01:20.00]like a spring--like each little molecule would be like a little spring
[00:01:26.21]and it would come down and shoot it off
[00:01:30.26]Melanie: Would you like this leaving the ball after
[00:01:34.07]or do you want it to just hang out in the ball?
[00:01:36.02]Jean: I guess it's sort of like when you clap your hands
you can feel it in both hands
[00:01:40.08]so you've got the same amount of feeling in both hands as they clap together
[00:01:43.26]which is sort of like how I picture the ball hitting the grass
[00:01:48.21]while the grass may deform and the ball doesn't
they're still hitting
[00:01:54.18]it's like a car hitting a brick wall, they're both gonna feel the same impact, right?
[00:02:00.00]Akbar: And so the ground is moving?
[00:02:02.17]Jean: The ground is moving.
[00:02:04.11]The ball is moving, cause it's pushing against the ground.
[00:02:08.06]But the ground is still gonna push back.
[00:02:12.26]Don: It's just remarkable how complex
[00:02:16.01]something so simple is
[00:02:21.11]and actually we're not even getting into
[00:02:23.27]the micro, what's really happening in there
[00:02:28.02]Akbar: I remember we were having that conversation last year
[00:02:31.27]...is it still moving?...so it's still moving!
[00:02:39.11]Jean: Yeah and I got into it a little bit with my students last year about
[00:02:42.02]"well, the object is moving because the molecules are moving"
[00:02:46.20]and I said, "No, this is where we have to separate the molecules from the object"
[00:02:51.29]and I said, "This is where it starts getting hard"
[00:02:53.19]and they're going "Ugh!"
[00:03:02.08]Akbar: I would differentiate cause it's like, technically, [00:03:05.15]we're all moving now even while we're staying still

[00:03:09.12]Jean: But the object is not moving