Energy diagrams need every storage mode

01
The tempting model
Calling energy 'lost' instead of moving it into thermal, spring, rotational, or internal storage.
02
Why it feels right
If the speed decreases, the energy seems to disappear from the visible motion.
03
Where it breaks · how to catch it
Your total energy bar shrinks without an external transfer out of the system.
04
The correct model
Energy is transferred or transformed. Track kinetic, gravitational, spring, rotational, thermal, and external work explicitly before saying mechanical energy is not conserved.
05
Repair · see it, then test it
worked example A sliding block stops because of friction. Where did its kinetic energy go?
Tempting move
It was destroyed.
Correct move
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.
Then practise it on the ladder
R16Net work changes kinetic energyadds: Work-energy uses the sum of all work terms.R19Frictional loss over a pathadds: Friction work depends on path length.