Axes are bookkeeping, not physics

The mistake

Thinking a tilted coordinate system changes which forces are real.

Why it feels right

Once axes are drawn along a ramp, the component arrows can start to look like new forces.

How to catch it

Your free-body diagram contains mg sin θ or mg cos θ as separate force arrows.

The first principle

Resolve vectors after listing real forces. Components are projections of one force into chosen axes; changing axes changes the algebra, not the interaction.

worked mini-example

A block on an incline has gravity mg downward. How many gravity forces act?

Common wrong move

Two: mg sin θ and mg cos θ.

Correct

One force, mg downward. Its two components are bookkeeping along chosen axes.

Test the repair NL-10 · transfer

On an incline, a student draws mg downward plus mg sin θ down the ramp. What should change?

Keep both arrows Remove mg and keep only its components as physical forces Keep mg as the force; use components only in equations Add a third gravity component

Make a fresh prediction before referring to the worked example.