Elizabeth Pate posted a comment asking about the reactions of AP readers:
I have a question about FRQ scoring. I use modeling instruction in my classroom so a few vocabulary terms that I use are different from a traditional physics course. For example, my students would call the normal force a flex force and the net force an unbalanced force. I do teach them both terms but I find they usually prefer flex and unbalanced force to Fnet and Fn, will these cause a problem for graders reading their FRQ's?
Reading AP exams is kind of how I learn about new trends in physics education. Last year I learned about a commercial device with two (visible) lasers and photoreceptors; when the beams are broken by a moving object, the device calculates speed. I'd call it a visible photogate. I forget what it's actually called, but enough students used this device on their lab problem that I found out about it.
So, "flex force," eh? That makes sense. Never heard it before. How would I react to it as an AP reader? It depends on the rubric, and how the problem is phrased.
When the test simply asks for a labeled free body, we are usually quite generous about those labels. My quintessential example was a few years back when students had to label a buoyant force, the force of water on a cup. We accepted "buoyancy." Then we accepted the misspelled "boyance". Then we accepted "bouncy," because it made sense in context. A rumor was spread that someone accepted "Beyoncé," but that's unconfirmed. :-)
So would I accept "Fflex" on a labeled free body? Possibly, especially now that I've heard from you that "flex force" is modeling vocabulary for "force of a surface on an object, acting perpendicular to the surface."
I always train the students to define their labels. Don't just say "Fn" -- say "force of the road on the car" or "force of the scale on the boy." Then even if someone misreads the label, or if the label is unintentionally ambiguous, there's no issue.
For example: we've never accepted "G" as a bare label for the gravitational force, even though some texts and teachers may teach that. Why not? Because "G" has a well defined conventional meaning: it's the universal gravitation constant, 6 x 10^-11 N*m^2/kg^2.
But a student who labels the diagram with "G" and then says "G: force of the earth on the car" earns full credit. Oh, and he can deal well with Newton's Third Law, too, but that's for a different post. :-)