The group discusses the shape of the speed-time graph and whether the cart's speed continues to increase after the push. After a trial they decide the graph should level off to a constant speed but drop straight down when it is stopped. In discussing where the hand was in contact they seem to agree on the common idea that the contact only initiates the increase in speed and that it continues to increase after contact is lost.
The group members express different ideas about the shape of the graph. They initially agree that there is a period of constant speed. In discussing where the hand is in contact Anna argues that because her hand moved with the cart while she was pushing it the contact lasted for a definite (albeit short) period of time. In preparing a whiteboard for the class discussion they consider both the shape of the graph and the contact period again.
Three groups present and explain their graphs to the class. The instructor guides the discussion to focus on the differences in their ideas about when the hand is in contact with the cart and summarizes the ideas the class has presented.
The group discusses the two ideas presented as a discussion between Kristen and Amara in STEP 3. Initially Anna agrees with Amara but Nikki dissuades her from this and so she then suggests that they agree with neither.
The group records a speed-time graph (and gets excited about it). Steph notes that (contrary to their prediction) the speed does not drop straight down when the cart is stopped. Wendy explains this in terms of the cart having to 'settle' on her hand when she stopped it.
Group 3 records data for STEPS 2 & 3. They then discuss the questions in STEP 4. They conclude that the speed changed when someone's hand interacted with the cart but stayed almost constant when there was not an interaction.
Anna and Faith discuss where on the speed-time graph the hand was in contact with the cart. Initially Anna thinks it is only at the beginning of the speed increase. In contrast Faith proposes it is all the time the speed is increasing. They settle of 'halfway' before trying it themselves. Not knowing about the delay in the data recording. Anna sees this as supporting her initial idea. They then watch the slow-motion movie and conclude that there is contact all the time the speed in increasing.
Two groups state that the speed of the cart stopped increasing when the hand was no longer in contact with it. Their reasoning is simply that contact with the hand is what makes the speed increase. When asked for evidence to support that idea Chris cites the slow-motion video they watched. Nikki then gives an explanation based on energy transfer from the hand to the cart.