Starts shaking it forcefully to separate particles (4)
I believe the answer is:
sift
'separate particles' is the definition.
'sift' can be an answer for 'separate' (sifting is a kind of separating). I'm not sure about the 'particles' bit.
'starts shaking it forcefully to' is the wordplay.
'starts' suggests taking the first letters.
The initial letters of 'shaking it forcefully to' is 'SIFT'.
Can you help me to learn more?
(Other definitions for sift that I've seen before include "Filter, riddle" , "Get lumps from (flour)" , "Use fist to pass through perforated container" , "Examine minutely" , "Separate out - examine closely" .)