Venezuelan President Chavez said in Moscow Sunday he had obtained a $2.2-billion line of credit from Russia for 90 T-72 tanks and an advanced long-range air defense system.

VOA: standard.2009.09.15

First, free velocity, constant velocity can be obtained for free without doing anything.

首先,速度是无偿的,恒定速度不需外力作用就能无偿获得

耶鲁公开课 - 基础物理课程节选