Momentum Chart
Also called Momentum bar chart
A momentum chart is a bar-style representation of the momentum carried by each part of a system before and after an interaction. AP Physics lists it as one of the representations students are expected to create and interpret.
College Board names momentum charts in two places in the AP Physics 1 course description: the appendix list of representations frequently used in the course, and the Science Practice 1 discussion, which offers pictures, motion maps, free-body diagrams, force diagrams, graphs, energy bar charts and momentum charts as examples. Both Physics C course descriptions list them too; the AP Physics 2 list does not.
The CED does not fix a layout. It names the representation without prescribing how to draw one, so treat any particular format as a teaching convention rather than an exam requirement.
What the bars have to do. Momentum is a vector, so bars point up or down according to the direction of travel once you have declared a positive direction. That is the whole reason the chart is worth drawing: with no net external force the total height of the bars after the interaction equals the total before, even when individual bars flip sign and even when the objects stick together. A bar for an impulse delivered from outside the system accounts for any change in that total.
The contrast with an energy bar chart is the point of having both. Energy bars are never negative and kinetic energy can be converted away into thermal energy or sound, so those totals need not match. Momentum bars can be negative and, for a chosen system with no external force, the total always does match. That is what is conserved in a collision.