The next minute (not included here in video), consist of Vesal misunderstanding Jared’s argument, and then Jared, Adolfo, and Alejandro rectifying that. Vesal then tacitly endorses that argument as correct.

Mischael interjects that Adolfo’s drawing supports the acceleration being zero.

Adolfo keeps drawing and elaborates, adding an asterisk to each sketch, before and after, marking the original location of the center of mass. , He explains that the CM cannot stay in that spot, “because it has to be closer to 2M.”

Mischael disagrees, “It is closer to the 2M, though,” and in the next segment he explains his reasoning.

Kimmee acknowledges and expands on Mischael’s reasoning, in terms of the two sides of the pencil expanding away from the center of mass. But she challenges that reasoning, now using objects on her desk to highlight that in the problem one mass is larger than the other.

Meanwhile, Adolfo changes the diagram to show a new location of the CM after the masses have moved apart.

Mischael explains how he sees the distance between the masses and the CM staying proportional even as the masses move.

Joel tries to explain his reasoning with numbers, thinking of the objects moving a million units apart, to show how that initial difference would become negligible. Others object to his using big numbers, and Joel drops that line of argument and loses the floor.

Mischael uses the numbers from Joel’s example to illustrate that proportionality is maintained even when the CM has a zero acceleration, and he heads to the board to explain. Vesal and Joel push against Mischael’s claim that the distances remain proportional. Mischael asks to explain his thinking at the board.

Mischael argues that because the two masses are accelerating “at the same rate away from one another,” the ratio D/L “will always stay the same.” Other students disagree; Jared argues that for D and L to be proportional, the CM needs to move (i.e. have a non-zero acceleration).

Alejandro steps up to the board and diagrams the “astronaut problem” (introduced in a prelecture and brought up earlier in the discussion) in which an astronaut throws a wrench in space. In that problem, the force on the astronaut is equal and opposite the force on the wrench. Since the wrench has a smaller mass, it has a proportionally greater acceleration. Alejandro uses numbers to show how the wrench moves farther, keeping the distances to the center of mass proportional. He then uses numbers for the present problem, in contrast: With M and 2M moving the same distances, the proportions change from the initial location of the center of mass.