moment

高舉你其中一隻手然後以肩膊為pivot打轉...這樣你就solve了physics mock 中的單車問題...當角度由40度增加到80度時....perpendicular distance between line of action of the force and the pivot will increase than decrease.... = =.....(我沒寫 of the force 就沒了1分....汗 = =") therefore the momentum changes

當大家在考試時若於著同樣問題大可做出以上動作....對理解題目有很大幫助

同時to 高舉了手說了一句: I really do have a question to ask......