impetus
/ˈɪmpɪtəs/noun
mass noun
1- the force or energy with which a body moves动力, 原动力：
hit the booster coil before the flywheel loses all its impetus.
在飞轮还没有失去所有动力前打一下启动线圈。
1.1
- the force that makes something happen or happen more quickly促进, 推动, 激励：
the crisis of the 1860s provided the original impetus for the settlements.
19世纪60年代的危机给开拓那些移民点提供了最初的推动力。
词源
mid 17th cent.: from Latin， 'assault， force'， from impetere 'assail'， from in- 'towards' + petere 'seek'.