Polio is no longer a concern in Western countries because of mass inoculations starting in the 1950s.

VOA: standard.2010.08.02

We don't say anything about implicitly here, we're talking about a closed system, so there's no mass leaving the system.

我们不讨论,这是隐含条件，因为我们讨论的是孤立系统，因此系统没有物质流失。

麻省理工公开课 - 热力学与动力学课程节选

If a photon which has no mass can behave as a particle, does it follow then an electron which has mass can behave as a wave? 1920.

如果一个没有质量的光子,能像粒子一样运动，那么它能像一个,没有质量的电子那样以波的形式运动吗。

麻省理工公开课 - 固态化学导论课程节选

And that's really neat to think about, because photons, of course, are massless particles, they have no mass, so it's neat to think about something that has no mass, but that actually does have a momentum.

而且那真的不容易想明白，因为光子，当然是无质量的粒子，它们没有质量，所以这个真的不容易想明白,一些物体没有质量，但是它们事实上确实有动量。

麻省理工公开课 - 化学原理课程节选

system is the opposite of the open system, no mass and no energy can flow through the boundary.

孤立系与开系正相反，没有质量或能量,能流过它的边界。

麻省理工公开课 - 热力学与动力学课程节选

It's no longer just a round spherical mass of cells, but it has some structure.

不再只是一个球状的细胞团,它有了一定的结构

耶鲁公开课 - 生物医学工程探索课程节选

We know there is no thing called a massless rope, but most ropes have a mass, but maybe negligible compared to the two blocks you are pulling, so we'll take the idealized limit where the mass of the rope is 0.

我们都知道无质量的绳子是不存在的,是绳子就有质量,但是相比于这两个物体就可以忽略不计了,所以我们有了这个理想的条件,即绳子的质量都是 0

耶鲁公开课 - 基础物理课程节选

If a proton which has no mass can behave as a particle does it follow that an electron which has mass can behave as a wave?

如果一个没质量的光子能像粒子一样,具有质量的电子能否,表现得像波一样吗？

麻省理工公开课 - 固态化学导论课程节选

If a photon, which has no mass, can behave as a particle --And we know this.

如果一个没有质量的光子，像粒子一样运动--，我们知道这个。

麻省理工公开课 - 固态化学导论课程节选