Energy diagrams need every storage mode

The mistake

Calling energy 'lost' instead of moving it into thermal, spring, rotational, or internal storage.

Why it feels right

If the speed decreases, the energy seems to disappear from the visible motion.

How to catch it

Your total energy bar shrinks without an external transfer out of the system.

The first principle

Energy is transferred or transformed. Track kinetic, gravitational, spring, rotational, thermal, and external work explicitly before saying mechanical energy is not conserved.

worked mini-example

A sliding block stops because of friction. Where did its kinetic energy go?

Common wrong move

It was destroyed.

Correct

Into thermal energy of the block/surface system.

Test the repair EN-10 · transfer

A bouncing ball returns to a lower height after striking the floor. Where is the missing mechanical energy?

Destroyed Converted mainly to thermal energy, sound, and deformation Stored as extra momentum Removed by the normal force with no other storage

Make a fresh prediction before referring to the worked example.