Mistake Master
Mistake Master · AP Physics C · Unit 2 · Topic 2.2 · Step-Through Animation
Every Arrow Says Who’s Pushing
You'll learnto draw a free-body diagram by naming every force 'on A by B.'
The Physics C convention is unforgiving and useful: every force is named “on A by B.” Shrink a block to a dot, hire one arrow per real force, and refuse any arrow that can’t fill in the “by” — starting with the famous phantom, the up-slope “force of motion.”
Before you start
What you're looking at
A 2 kg block sliding up a rough 37° incline after a shove — hand gone — with an empty free-body diagram waiting on the right.
The question
Which force arrows actually belong on this block?
Watch for
The tempting fourth arrow up the slope — a 'force of motion' — that no source can be named for.
What the symbols mean
Every real force is named 'force on A by B'; the dot is the block; the incline sits at 37°.
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