Then you guys know, you just told me, acceleration is -9.8, We call it "minus" because it's accelerating down and up was taken to be the positive direction.

然后你们都知道,你告诉我,加速度是-9.8,我们取负号是因为加速度方向朝下,而正方向为竖直向上

耶鲁公开课 - 基础物理课程节选