摩擦
mó cā · HSK 5
friction
🔥 摩 mó = rub/grind + 擦 cā = wipe/scrub — both verbs for surface contact
摩 (rub, as in 按摩 massage) plus 擦 (wipe, as in 擦黑板 wipe the blackboard) stack two near-synonyms for surface contact. Together they name the physical effect (friction) and extend to social meaning (disharmony between people).
擦 — hand radical 扌 + 察 (chá, inspect)
擦 is a phono-semantic compound. The hand radical 扌 indicates the meaning — an action done with the hand, namely rubbing, wiping, or scrubbing. The right side 察 supplies the sound, giving the modern reading cā. The character is relatively late and has always centered on the idea of friction by hand.