transcript showing concern about using word force, and force relating to mechanism

This post relates directly to my other posts - and probably doesn't make much sense as a stand-alone, but the idea is basically these two points:

- how are they using the word mechanism, and do we need to be more clear about it

- do they feel inhibited to use the word force, and is this problematic?

here's the transcript (video is joe buoyancy mechanism) - my main points of interest are in color. The purple bit is the real gem - the red bits are also interesting. I'm concerned that Tim is referring to an outside authority - not a negotiated meaning of mechanism. No one else seems to see it that way - he's the only one clear about it, but it isn't his construct. It's also interesting how Bruce keeps wanting to only talk energy but uses force terms like push. Bruce is basically pushing this whole reconciliation of their two explanations because of Tim's use of the word buoyancy in the whiteboard diagram - Tim says it is problematic because they should only talk energy. I think bringing up COM is interesting here, Bruce says 'that's one spot that's gravity' - I think Bruce is seeing bringing up COM as requiring a force explanation, where only energy is needed. He has a good point there and it's dropped completely. Energy explanations don't require the particle model, but Tim is relying on one. Mostly I'm still wowed by their negotiation of mechanism... I hope this is clear below:

J = joe, mic wearer

M = mary lady in pink shirt

L = lady in blue jacket

B = bruce in green jacket and grey t-shirt

T = tim in blue t-shirt

C = Chris

[B] Tim can you show me your explanation (points to the whiteboard)

[T] um the water is going to push down on the ball right?

(the females are having a side conversation here i'm ignoring until they join tim and bruce - joe is silent through this)

[B] the water is going to push down the ball?

[T] well the water is pushing down so it's going to displace the ball

[B] no it's going to displace the water

[T] it's going to displace the ball - why does the ball float

[B] are you going back to buoyancy? I'm going back to energy

[T] buoyancy is the - gives the ball kinetic energy

[B] i'm going back to KE - i'm going back to this. Here's my original level of the water, right? you know i should say this is my original level of the water right? (he's pointing/drawing on the whiteboard?) i have this ball, i push it down, it says hey water get out of the way because i'm coming down here so the water can not go any other way except up

[T] uh huh

[B] so the water continues up

[00:01:14.29]

[B] the water is being displaced - i'm doing this in terms of energy so what i have now is

[T] so what have you done...

[B] i have this block here of water, this is my displaced water

[T] what if you take it sort of that the ball is already under water level and you don't have to worry about the higher..

[B] you still got all this i have to push it down

[T] that doesn't matter but what have you done to the PE of the water

[B] what i've done is i've raised the water level, ok, i've and the water wants to come back down again so i have increased the the height of the water ...

[C] the gravitational potential energy

[B] right i've increased GPE of the water so you showed it that way and then i'm saying that the water wants to come back down so now i'm holding this down here when i let go the water says um

[C] but it

[B] the water wants to come back down and take the place of the ball

[00:02:16.07]

[B] and so the ball moves up say a little bit but when it moves up from here to up there it pushes some of the water

[C] out

[B] yea it helps push it away so actually what i think is going on is that the water is going like that as well as the ball is moving straight up

[M] when you let go

[B] yea and and then it ... (drops the whiteboard marker on the diagram)

[T] that's when it reaches the top

[B] it never reaches the top totally right?

[T] it doesn't need to

[M] if it stops it might

[B] but that's my interpretation but to draw it is to here (can't quite hear but he's again dropping the marker on the drawing)

[T] ok, that's fine but the way tod (some discussion about the name of the guy with others chiming in) he talked he simplified he said you only have to consider the center of mass of the water

[B] ok

[T] so to push the ball down you raise the center of mass of the water

[B] ok

[00:03:26.23]

[T] so when that goes down you've lost Gravitational potential and its transferred that to KE of the ball

[C] can you say that again louder ...

[T] so you have the center of mass of my cup of coffee (he lifts it up) is is right there and

[B] there's all different ways to model this

[T] uh if i push something in there i raise the level somewhat but it doesn't matter it's i've raised the COM of that cup of coffee and that's really what you can consider ... active in COM instead of worrying about all the... details of the system (I can't quite get this)

[B] so

[T] the point was that the ball at the bottom has buoyancy it's because the the water has GPE and .. the COM can fall so the COM of the water goes down it loses PE transfers that to KE of the ball, ball increases in KE and i've also got like a bit of feedback where because you have drag with resistance in the water it's transferring KE back to the water

[B] oh that's interesting

[C] so you're thinking it's GPE of the water that it's falling.. pulled down so it's pushing

[T] yea... (can't hear) i mean it doesn't matter to overanalyze that part it's just that water the COM of the water goes down the ball goes up the ball goes into motion so you don't have to worry about forces necessairly but but the object's got buoyancy usually (?) here and it's drag here (pointing to the diagram) usually so, it's simple enough

[B] the only reason i'm just sharing this scenario is because i wanted to keep it all with energy

[00:05:21.23]

[B] rather than COM and buoyancy

[T] well COM just tells you how you can look at position of the water

[B] that's one spot - that's gravity...

[T] well you're talking about GPE so it acts on you can take that COM of the water as as the point where it acts on

[B] right..... ok i just thought it should be all because this is all about energy i thought he wanted us to keep it more to energy

[T] this is in terms of energy

[B] yea although you had the word buoyancy in there

[T] i don't see a problem - that's the mechanism

[B] you're going to call that the mechanism

[T] that's how it transfers it's you know like the interaction that causes that to action (?) this KE transfers because of buoyancy this KE transfers because of drag

[C] so those are the forces

[T] umm.. yea they generalize them as interactions not necessairly forces... because friction..

[B] ok

[C] who generalizes who genera i said they generalize it so i'm going to ask who

[T] the smart people with hats um i did a pilot there's this interactions.. they used that format and i've seen it somewhat in biology...