Centripetal acceleration points inward
The mistake
Drawing a “centrifugal” force outward on a body in circular motion.
Why it feels right
You feel flung outward in a turning car, so it seems a force pushes out.
How to catch it
Your free-body diagram has a net outward arrow for something moving in a circle.
The first principle
The net force is centripetal — inward — supplying a = v²/r. The outward 'feeling' is inertia in a rotating frame, not a real force in the ground frame.
worked mini-example
What real force keeps a car turning on a flat road?
Common wrong move
An outward centrifugal force balanced by friction.
Correct
Inward static friction alone; it is the centripetal force.
Test the repair NL-05 · transfer
Make a fresh prediction before referring to the worked example.