Explosions conserve momentum while kinetic energy can increase
The mistake
Assuming an explosion violates momentum conservation because pieces fly apart.
Why it feels right
The motion appears from nowhere, so momentum seems to be created.
How to catch it
You say total momentum after an internal explosion is nonzero for a system initially at rest.
The first principle
Internal energy can become kinetic energy, but internal forces occur in equal/opposite pairs. Without external impulse, total momentum is conserved.
worked mini-example
A firework at rest explodes into fragments. What is total momentum immediately after?
Common wrong move
Positive because fragments move outward.
Correct
Zero vector; fragment momenta add to the initial zero.
Test the repair MOM-06 · transfer
Make a fresh prediction before referring to the worked example.