I have it shown with the--the vertical lines on this chart indicate recessions and this shows--this is from 1948 to 2007 and every recession that we've had since 1948 is shown.

我用图中的这些垂直的线表示,从1948年至2007年的经济衰退,从1948年以来的每一次衰退

耶鲁公开课 - 金融市场课程节选

For example, suppose you use vertical motion and you use y instead of x; and a would be g or -g; that's a particle falling down under the affect of gravity.

例如,假设在竖直运动中,你用 y 来代替 x,那么 a 就是 g 或者 -g,这就是一个受重力作用下落的质点

耶鲁公开课 - 基础物理课程节选