Crossword Genius

Potassium density fluctuates with force and atomic explosive (5,2,8)

Ross

I believe the answer is:

stick of dynamite

I'm a little stuck... Click here to teach me about this clue!

Here is my best explanation:

'explosive' is the definition.
I don't know anything about this answer so I can't judge whether it can be defined by this definition.

'potassium density fluctuates with force and atomic' is the wordplay.
'potassium' becomes 'k' (K is the chemical symbol for potassium).
'fluctuates with' indicates an anagram (I've seen 'fluctuating' mean this).
'force' becomes 'f' (symbol used in Physics e.g. f=ma).
'and' says to put letters next to each other (I've seen this in other clues).
'k'+'density'='kdensity'
'f' put after 'atomic' is 'atomicf'.
'kdensity' anagrammed with 'atomicf' makes 'STICK OF DYNAMITE'.

Can you help me to learn more?