divide
劃 centers on the act of dividing or marking a boundary, as if drawing a line to separate one area from another.
劃 combines 畫 (draw, mark) with 刂 (knife), suggesting dividing by drawing a line or cutting. The exact historical development is uncertain, but the component relationship is clear.
The left side 畫 looks like a brush drawing a line, and the right side 刂 is a knife. Together they show dividing something by drawing a cutting line.
For カク, imagine drawing a dividing line on a canvas with a quick, sharp stroke: the sound of the stroke is 'kak', like a knife cutting, which cues カク.