The group first briefly discusses whether an interaction is occurring when an object slows and stops. They then discuss the child sliding on a wet plastic sheet, and decide there are unknown factors that would affect their answer.
Wendy expresses Group 9's idea that friction 'eats up the kinetic energy'. Chris describes his group's thinking about water acting as a 'barrier' to frictional effects, but does not completely eliminate them. In presenting their ideas about the second question, Group 3 brings up their thinking about the factors that could affect what happens. Finally, Grace proposes a friction-based explanation for why the child would eventually stop, even on a very long sheet.
Right at the end of the class period, Group 3 discusses how to complete the G/R energy diagram and the energy statement for the block slowing down as it slides across the table. Though they are not deeply engaged at this point, they do come up with an appropriate response.
Seeing the cart decrease in speed quite quickly, the group agrees that this is due to the interaction between the friction pad and the track. They then discuss what type of interaction this is. Initially they call it a 'push/pull' but then are not sure because it seems different to previous examples of contact push/pull interactions they have seen.
(Faith was not present for this class period.) In Step 3, the group discusses why the rate of slowing is less than it was in Step 2. In Step 4, they decide that the cart moves at a constant speed after the initial push. They then discuss what the motion would be like in a truly frictionless environment.
In discussing their predictions, it seems that Karen and Nikki think the speed will be constant when there is no friction, whereas Anna thinks the speed will still decrease slightly. On watching the simulator movie, Anna explains the constant speed section by saying that 'nothing is pushing it either way'.
The group discusses how to describe a child decreasing in speed as they slide on a plastic sheet in terms of energy. They discuss what objects they should take as the energy giver and receiver and what types of energy change in each. Nikki makes an analogy to a block sliding across the table, but the group members are not sure whether the child has a decrease in kinetic energy or chemical potential energy. The instructor monitors their discussion (as well as those of other groups) while circulating around the room.
Nikki asks the instructor for help in deciding what type of energy decreases in the child. The instructor tries to guide the group by asking about the evidence for changes in different types of energy. It then becomes evident that the group has not yet isolated the interaction of interest and the instructor discusses this important step with them. The instructor's decision to have this conversation was based on previous monitoring of the group and the judgment that it was needed to help the group move on.
The class responds to a clicker question with almost everybody agreeing that when an object slows down, an interaction is always responsible. Maggie uses an example of a car on gravel road to explain Group 4's thinking.
Two groups present their energy diagrams to the class. There is a discussion as to whether it is appropriate to include an increase in thermal energy for the cart as it slows down. Dawn and Chris argue that, since the slowing is due to a friction type contact push/pull interaction, then both the cart and track will warm up.
Almost the whole class responds to a clicker question by choosing that, in the absence of any interactions, a cart would move a constant speed. However, Maggie thinks it will eventually slow down and Sam seems to think it will continue to increase. Steph reasons that it will remain constant because there is nothing to change it. When asked to support their answers using ideas about energy, Anna reasons that it cannot be increasing because there is nothing giving it energy. Maggie states that with no energy transfers, there cannot be a change of speed.
In a clicker question, most of the class agrees with Daryl. However, Group 4 agrees with Luisa because they still seem to be holding on to the idea that the speed can increase, even after the interaction has stopped. Dawn argues that the evidence they have does not support this, and seems to convince Group 4. Group 2 says they chose "neither" because Daryl did not discuss the decreasing speed after the push.
Groups 5 and 3 present their explanations and agree that both the child and sheet increase in thermal energy. Dawn raises the issue of whether there is a decrease in chemical potential energy or kinetic energy associated with the child ( a question that Group 3 struggled with earlier). This opens an important discussion on what interaction should be the focus of this explanation and then Wendy presents her written narrative.