National Hockey League players it was U.S. will again be playing for their countries when the men's hockey competition hits the ice on February 16.

VOA: standard.2010.01.12

So a closed system would be, for instance, a glass of ice water with an ice cube in it, with the lid on top.

因此闭系可以是，比如说，一杯放了,一个冰块的冰水，顶上加了盖子。

麻省理工公开课 - 热力学与动力学课程节选