This is treating momentum as a 2D vector for now: later some 1D treatments might follow. These are experimental! This one introduces the box: velocity and mass are the compensated quantities.
The values of mass and velocity determine the lengths of the sides of the box, and so the area, which represents the momentum. To compare two, you'll need two boxes.
Collisions might require multiple boxes to represent the momenta. Perhaps two before and two after. The screen is going to get full, so compress the representations a little to restore focus and clarity.
But a more restricted choice might be (pedagogically) best, allowing the comparison of simple ratios of mass.
A target might be have a representation to explore the angle between the trajectories of two objects of equal mass, one initially stationary. This requires an elastic collision, so we jump ahead and borrow from the energy description.
The shifters (which are discrete to help(?)) and the grids allow you to compare the momenta and energy. Here is another way of doing the comparison.
I’m quite pleased with this — a graphical exploration that keeps the physics to the fore, and the algebra to the rear. A proof
of necessary connection that is usually just stated.