Even though the graph is going up and down, the object is moving from left to right.

虽然图上曲线是上下波动,但是物体是由左向右移动的

耶鲁公开课 - 基础物理课程节选

So what we would like to do is to describe what the object does by drawing a graph of time versus space and the graph would be something like this.

然后我们要做的就是描述这个物体的运动,通过画一个"x-t"图,画出来的图就像这样

耶鲁公开课 - 基础物理课程节选