see people with them, and what happens here is it's supposed to be those noise cancellation headphones. All they do is they take in the ambient noise that's around it, and there's actually battery in the headphones, that then produces waves that are going to destructively interfere with that ambient noise.

我从来没有用过这个,但你会看到有人带他们,它们可以作为消噪音耳机,它们所做的就是采入,周围的随机噪声，耳机里面是，有电池的，然后它能产生和,随机噪声相干相消的声波。

麻省理工公开课 - 化学原理课程节选

By the way, that's a very remarkable property of the gravitational force-- the cancellation of the two ms.

顺便说一下,这是重力的一个重要属性,即可以消去等式两边的 m

耶鲁公开课 - 基础物理课程节选

As long as we understand that, we can do this cancellation and this says on the left-hand side the change in the quantity v square over 2 is a times the change in the quantity x.

只要我们明白这一点,我们就可以这样做简化,在等号左边,v^/2的变化量,为a乘以x的变化量

耶鲁公开课 - 基础物理课程节选