And I have purposely made the arrow shorter to indicate that it has been slowed because we are going to argue its mass didn't change, so the only way to change its energy is to change its velocity.

我已经故意将这个箭头弄短,用来象征它变慢了,因为我们将证明它的质量没有变，只有它的能量改变了,也就是它的速度变了。

麻省理工公开课 - 固态化学导论课程节选

This is another familiar picture, I purposely picked one that looked sort of old fashioned compared to the usual way you see this, which might be on the nightly news.

这是另一幅熟悉的图片,我有意选择了,与你们通常在晚间新闻见到的那种相比,看上去,比较老式的设备

耶鲁公开课 - 生物医学工程探索课程节选

So, what we have found out so far, I'm purposely going from x to y because I want you to know that the unknown variable can be called an x or can be called a y.

到目前为止,我们有这些结论,我特地把x换成y,因为我想让你们明白,未知变量既可以写成x,也可以写成y

耶鲁公开课 - 基础物理课程节选